The new material is a chiral multiple quantum well structure built from layered two-dimensional halide perovskites. Quantum wells are thin sheets of semiconductor sandwiched between barriers, so thin that carriers are confined in one dimension and their electronic states become quantized, much like the discrete energy levels of an atom. In conventional perovskite quantum wells, each well has a fixed thickness determined by the organic spacer cations that separate the inorganic lead-halide sheets, and films typically contain a distribution of well widths, known as phases, coexisting within the same material. The researchers exploited this natural phase diversity deliberately: they constructed oriented films in which every quantum well phase, regardless of its width, is intrinsically chiral, meaning its structure lacks mirror symmetry and can exist in left- and right-handed forms.

Chirality is the key ingredient because of a phenomenon known as chiral-induced spin selectivity, or CISS, in which electrons of one spin orientation pass through a chiral structure far more readily than electrons of the opposite spin. The effect, long studied in DNA and other helical molecules, was demonstrated in chiral lead-halide perovskites in 2019, when spin-dependent charge transport through two-dimensional chiral hybrid perovskites was first reported. Subsequent work showed that a spin light-emitting diode operating at room temperature could be built from such materials, and in 2024 researchers demonstrated room-temperature spin injection across a chiral perovskite interface into a conventional III-V semiconductor. The bottleneck, as the new study emphasizes, is that spin polarization at the device level remains small because spins are lost rapidly at interfaces and in the bulk of the material, before they can accumulate or be extracted.

The team’s solution is conceptually elegant: instead of fighting spin relaxation at a single interface, they turn the whole layered structure into a spin cascade. Because the quantum wells in their film have varying widths, their electronic energy levels vary slowly and continuously across the different phases. Spatially, the wells of different widths are coupled to one another, so photoexcited carriers can funnel energetically downhill from wider-bandgap narrow wells into narrower-bandgap wide wells. Critically, because each well is chiral, every step along this energy descent is also a spin-selective polarization stage. Rather than generating spin polarization once and hoping it survives a perilous journey to a device contact, the structure regenerates and reinforces polarization at consecutive intermediate states, so that spin information is repeatedly refreshed as carriers move through the stack.

To build these structures, the researchers developed a seed-assisted crystallization process that forms the chiral multiple quantum wells in situ, producing oriented films in which the chirality is continuous across all quantum-well phases. They measured an average circular dichroism dissymmetry factor of 1.5 × 10⁻², a quantitative gauge of how differently the material absorbs left- and right-circularly polarized light, confirming that the chiral character is robust and uniform throughout the film rather than confined to one selected layer. This continuity is what distinguishes the new architecture from earlier chiral single quantum well designs, in which only one well width carried the chiral imprint and the surrounding achiral phases acted as spin sinks.

The consequence of the cascade is a dramatic extension of spin coherence. Using circularly polarized transient absorption spectroscopy, a pump-probe technique in which a spin-selective laser pulse tags the carrier population and a delayed probe tracks how long the spin imbalance persists, the team measured spin coherence lifetimes of approximately five nanoseconds at room temperature. In the world of spin physics, where room-temperature spin lifetimes in bulk halide perovskites have generally been measured in the sub-nanosecond to few-nanosecond range and can be far shorter in other solution-processed semiconductors, five nanoseconds is a meaningful reservoir of spin information, long enough for carriers to be transported, recombined or extracted with their polarization substantially intact.

The payoff appears directly in the light the material emits. The long-lived spin population produces circularly polarized luminescence with a luminescence dissymmetry factor of 1.4 × 10⁻², meaning the emitted light is measurably helical, carrying spin information encoded in the handedness of its polarization. Circularly polarized light is itself a valuable commodity: it is needed for spin-resolved displays, for optical communication schemes that encode data in polarization states, for quantum information protocols that use photon polarization as a qubit, and for chiral sensing, where the circular polarization of probe light interacts selectively with chiral molecules such as pharmaceuticals and biomolecules. Achieving strong, stable circular polarization from a solution-processable semiconductor at room temperature has been a persistent challenge.

The researchers also translated the long spin lifetime into working devices. Spin-dependent charge transport through the chiral films reached a polarization degree of over 80 percent, a figure indicating that the vast majority of transported carriers preserve their spin orientation, consistent with the CISS effect operating efficiently across the cascade structure. On this foundation the team demonstrated two applications. The first is X-ray-triggered dissymmetric photopolymerization, in which circularly polarized emission initiated by X-ray excitation drives a polymerization reaction in a way that distinguishes left- from right-handed product formation, a demonstration of how spin-polarized perovskites could influence chemical synthesis. The second is a circularly polarized light photodetector that the team reports as high-performing, converting the helicity of incoming light into an electrical signal.

What makes the advance notable from a materials chemistry standpoint is that it does not require exotic processing. Halide perovskites are celebrated for their solution processability and self-assembly, and the seed-assisted crystallization strategy harnesses the natural tendency of these materials to form multiple well-width phases, recruiting the phase mixture into functional service rather than suppressing it. The theoretical analysis provided by co-author Zhi-Gang Yu supports the picture of consecutive intermediate polarization states established by the slowly varying, spatially coupled wells, giving the empirical observations a coherent mechanistic framework rooted in the interplay of chirality-induced spin-orbit coupling and quantum confinement.

The broader implications reach into several converging fields. For chiroptical photonics, the work supplies a route to long-lived spin coherence in an easily processed material family, easing the construction of polarization-encoded light sources and detectors. For spintronics, it suggests that lossy interfaces, long the nemesis of spin injection, can be compensated architecturally by cascading many modest spin filters in series, a design principle transferable to other chiral semiconductors. And for perovskite research at large, it adds spin functionality to a material platform already excelling in solar cells, LEDs and radiation detectors. The authors frame the result as opening the way to long-lived spin coherence in halide perovskites and promoting their use in chiroptical and spintronic devices, and on the evidence presented, the five-nanosecond spin lifetime, the 80 percent transport polarization and the functional demonstrations together mark a substantial step toward spin-based technologies that operate not in cryogenic laboratories but at the temperatures of everyday life.

Subject of Research: Spin coherence extension in chiral perovskite multiple quantum wells via spin cascade

Article Title: Perovskite chiral multiple quantum wells with extended spin lifetime via efficient spin cascade

Article References: Qiu, J., Huang, Y., Wong, P. Y., Chang, K. T., Xue, J., Chen, Z., Wang, Z., Yao, J., Yu, Z.-G., Chen, X., & Lu, H. (2026). Perovskite chiral multiple quantum wells with extended spin lifetime via efficient spin cascade. Nature Photonics. https://doi.org/10.1038/s41566-026-02027-6

Image Credits: AI Generated

DOI: 10.1038/s41566-026-02027-6

Keywords: halide perovskites, chiral multiple quantum wells, spin cascade, spintronics, spin coherence lifetime, chiral-induced spin selectivity, circularly polarized luminescence, quantum wells, room-temperature spin, circularly polarized light photodetectors, Nature Photonics, Perovskite

The heart of the problem lies at the interface between the perovskite light absorber and C60, a spherical carbon molecule resembling a microscopic soccer ball. In inverted, or p-i-n, perovskite solar cells, C60 sits directly on top of the perovskite film and serves as the electron-selective contact, whisking photogenerated electrons toward the external circuit while blocking holes. It is cheap, sublimable, chemically compatible with the delicate perovskite crystal, and forms smooth, uniform films. Yet devices built with C60 contacts consistently suffer from severe non-radiative recombination at that interface, a process in which photoexcited electrons and holes annihilate each other as heat instead of contributing to current or voltage. Previous research campaigns attacked this problem by passivating electronic trap states on the perovskite surface, assuming the perovskite itself was the defective party. Those efforts helped, but the recombination losses never fully disappeared, and the true origin of the loss remained maddeningly obscure.

The Singapore-led team approached the mystery from a different angle: instead of interrogating the perovskite, they scrutinized the electronic structure of the C60 film itself. Using density functional theory calculations, they showed that when C60 molecules pack closely together in a crystalline film, their lowest unoccupied molecular orbitals, the LUMOs, overlap strongly from molecule to molecule. This intermolecular coupling transforms what would be discrete, isolated molecular levels into extended, band-like electronic states that spread across the fullerene film and reach all the way down to the perovskite surface. In isolation, a single C60 molecule is a poor recombination center. But when its LUMO levels merge into a delocalized band that hybridizes with states at the perovskite surface, the interface gains an energetically accessible pathway for electrons and holes to meet and recombine non-radiatively.

To quantify how damaging these band-like states are, collaborators at the University of Potsdam computed carrier capture coefficients for the hybridized interface states, drawing on the multiphonon emission framework that describes how carriers shed energy into lattice vibrations. The calculations indicated that the C60-derived band-like states act as highly efficient recombination conduits, explaining why even well-passivated perovskite surfaces lose voltage the moment C60 is deposited on top. The team confirmed this experimentally by measuring quasi-Fermi-level splitting, a proxy for the maximum voltage a solar cell can deliver, before and after C60 deposition. Depositing pristine C60 onto an already passivated perovskite surface slashed the quasi-Fermi-level splitting by a striking 89 millielectronvolts, a loss large enough to shave roughly a full percentage point off the achievable efficiency.

The remedy the researchers devised is as chemically simple as it is conceptually elegant. Rather than modifying the perovskite, they exposed the C60 film to a vapor of trialkylamines, specifically a long-chain amine designated C18N. The amine molecules intercalate between the buckyballs, wedging them apart and disrupting the ordered molecular packing that enables LUMO overlap. X-ray diffraction measurements using grazing-incidence geometry at the Shanghai Synchrotron Radiation Facility documented the resulting loss of crystallinity in the fullerene film, while time-of-flight secondary ion mass spectrometry confirmed that the amine species distribute through the C60 layer. Transmission electron microscopy provided direct visual evidence of the structural changes. Crucially, the treatment preserves the electronic function of the contact: the decoupled C60 still conducts electrons efficiently, but its LUMO-derived band-like states are substantially weakened, closing the recombination channel at the perovskite interface.

The electrical consequences were immediate and dramatic. The quasi-Fermi-level splitting loss after C60 deposition dropped from 89 millielectronvolts to just 41 millielectronvolts with the amine treatment alone, and fell further to 17 millielectronvolts when combined with conventional perovskite surface passivation. In other words, the team recovered nearly all of the voltage that the fullerene contact had been silently destroying. Photoluminescence quantum yield measurements and impedance spectroscopy corroborated the reduction in non-radiative losses, and femtosecond transient absorption experiments traced the extended carrier lifetimes that result from shutting down the interfacial recombination pathway.

Translated into full devices, the interfacial engineering delivered inverted perovskite solar cells with a certified power conversion efficiency of 27.2 percent and a stabilized output of 26.6 percent on an active area of 1.02 square centimeters. That certification matters: laboratory efficiency records are sometimes reported on tiny cells measured under non-standard conditions, whereas this result was independently verified on a device large enough to be technologically relevant. The achievement places these cells among the most efficient single-junction perovskite devices ever reported and demonstrates that the remaining headroom to the theoretical Shockley-Queisser limit is increasingly limited by losses that engineers can now name, locate and suppress.

Efficiency alone does not make a solar technology viable; stability under real-world conditions does, and this is where perovskites have historically stumbled. The amine-treated devices proved remarkably resilient, retaining more than 98 percent of their initial efficiency after 1,000 hours of continuous illumination under ambient air, without protective encapsulation tricks beyond standard device architecture. This durability suggests that loosening the fullerene packing does not introduce new degradation pathways, and may even contribute to interface robustness by reducing the recombination-driven heating and ionic stress that accelerate failure. For a technology often criticized for degrading within months, thousand-hour endurance at near-record efficiency is a persuasive counterargument.

Beyond the headline numbers, the study carries a broader conceptual lesson for the field. For years, passivation strategies have focused almost exclusively on the perovskite side of every interface, treating the transport layers as chemically inert bystanders. This work demonstrates that the transport layer’s own electronic structure, down to the way its molecules pack and couple, can be the dominant source of recombination. The implication extends well beyond C60: any molecular contact material whose frontier orbitals delocalize into band-like states could be quietly sabotaging device performance, and the same intermolecular decoupling logic could be applied to organic semiconductors, small-molecule contacts and even the charge-selective layers in tandem and multi-junction architectures.

The research also showcases the power of combining atomistic simulation with synchrotron characterization and device engineering under one coordinated program, spanning institutions in Singapore, China and Germany. With perovskite-silicon tandems now approaching and exceeding 29 percent efficiency, every millielectronvolt of interfacial loss recovered translates directly into commercial advantage, and the trialkylamine vapor treatment is a low-cost, scalable post-deposition step compatible with existing fabrication flows. One of the corresponding authors, Yi Hou, is the founder of a perovskite commercialization company, underscoring how quickly laboratory insights of this kind are flowing toward manufacturing. If the buckyball’s destructive band-like states can be tamed with a puff of amine vapor, the path from record-setting cells to durable, mass-produced perovskite modules looks considerably shorter than it did before this interface was finally understood.

Subject of Research: Suppressing interfacial recombination at the C60 electron-selective contact in inverted perovskite solar cells through vapor-phase trialkylamine passivation

Article Title: Intermolecular decoupling of C60 suppresses interfacial recombination in perovskite solar cells

Article References: Wang, T., Luo, R., Chen, J., Hu, J., Wang, X., Gundermann, R., Wang, P., Dong, Z., Su, Z., Zhu, Z., Du, X., Li, J., Tian, H., Guo, X., Wang, Y., Lin, M., Xing, Z., Wu, M., Ji, R., … Hou, Y. (2026). Intermolecular decoupling of C60 suppresses interfacial recombination in perovskite solar cells. Nature Photonics. https://doi.org/10.1038/s41566-026-02030-x

Image Credits: AI Generated

DOI: 10.1038/s41566-026-02030-x

Keywords: perovskite solar cells, C60 fullerene, interfacial recombination, trialkylamine passivation, electron transport layer, power conversion efficiency, non-radiative recombination, quasi-Fermi-level splitting, vapor-phase treatment, device stability, Nature Photonics, photovoltaics

The core of the problem lies at the boundary between the two light-absorbing materials inside an organic photovoltaic cell. When a photon is absorbed, it creates a tightly bound electron-hole pair, an exciton, which must travel to the interface between the electron-donating polymer and the electron-accepting molecule to be split into free charges. In the process, an interfacial charge-transfer state forms, in which the electron and hole sit on adjacent molecules. These charge-transfer excitons are the workhorses of charge generation, but they are also a liability. Because they are spatially separated, their electron and hole wavefunctions overlap only weakly, which means they couple poorly to light. They cannot easily emit a photon, and instead they tend to decay non-radiatively, releasing their energy as molecular vibrations and heat. Every charge-transfer exciton lost this way erodes the open-circuit voltage, the maximum voltage the cell can produce, and therefore the overall efficiency.

The research team, led by Yingze Zhang and Sai Ho Pun of the Hong Kong University of Science and Technology together with Gang Li of the Hong Kong Polytechnic University and colleagues, approached the problem not by redesigning the morphology of the blend or tweaking the energy levels of the frontier orbitals, the two conventional levers of organic photovoltaic optimization, but by adding an entirely new photophysical channel. Their idea was to introduce a small fraction of a solid-state emissive guest acceptor, a molecule based on a tetraphenylethylene, or TPE, core, into a state-of-the-art host system built around Y-series non-fullerene acceptors. The guest is chosen so that its localized excited state, the excited state confined to a single molecule, sits energetically close to the charge-transfer manifold at the interface.

This energetic resonance is the key to the whole scheme. When an interfacial charge-transfer exciton forms, it normally faces a choice between radiative decay, which is slow and improbable, and non-radiative decay, which is fast and dominant. But if a localized excited state of the host acceptor lies just slightly above the charge-transfer state, thermal energy at room temperature is enough to push the exciton back up onto that localized state. From there, the excitation can hop onto the emissive guest molecule through resonance energy transfer, the same near-field mechanism that transfers energy between closely spaced fluorescent dyes. The guest, engineered to luminesce strongly even in the solid state, then has a real chance of emitting a photon. The result is an indirect but effective radiative recombination pathway: charge-transfer excitons that would otherwise be lost as heat are thermally recycled into bright, emissive states.

Establishing that this counterintuitive route actually operates required an extensive experimental and computational campaign. The team grew single crystals of the TPE-based acceptors to resolve their molecular packing, confirming that the twisted tetraphenylethylene core suppresses the tight pi-pi stacking that normally quenches emission in organic solids. Photoluminescence quantum yield measurements showed that the guest molecules retain strong solid-state emission when blended into the host. Transient spectroscopy, including time-resolved photoluminescence and electroluminescence measurements performed with collaborators at Zhejiang University, traced the flow of excitation from the charge-transfer states to the localized states and finally to the emissive guest. Molecular dynamics simulations, run with the GROMACS package, mapped the distribution of intermolecular distances and demonstrated that the energetic resonance between the charge-transfer and localized manifolds is thermally accessible across realistic molecular configurations.

The device-level consequences are striking. Cells containing the emissive guest acceptor showed markedly enhanced electroluminescence quantum efficiency, the fraction of injected charges that emerge as photons when the device is driven like a light-emitting diode. Because electroluminescence and the reverse process of non-radiative recombination are two sides of the same coin, this enhancement translates directly into suppressed voltage loss. The team measured a non-radiative voltage loss as low as 0.142 electronvolts, an ultralow figure by the standards of organic photovoltaics, where losses of 0.2 to 0.3 electronvolts are common. Crucially, the guest did not compromise the other pillars of device performance: charge generation remained efficient, charge transport was preserved, and devices still delivered power conversion efficiencies of around 17 percent in the binary host system.

The full payoff came when the strategy was combined into a ternary blend, in which the donor polymer, the host acceptor and the emissive guest acceptor coexist in a single active layer. The resulting single-junction devices achieved a power conversion efficiency of 21.2 percent, independently certified at 20.84 percent, with an open-circuit voltage of 0.93 volts. For a single-junction organic solar cell, these numbers place the work at the very front of the field, and the certified figure matches or exceeds the best values reported for any organic photovoltaic architecture to date. The fact that the gain comes from reducing a fundamental loss channel, rather than from squeezing more current out of the absorber, suggests the approach is complementary to, rather than competing with, existing optimization strategies.

What makes the result conceptually important is the reframing of how energy loss should be fought. For years, the community has pursued two main routes: controlling the nanoscale morphology of the donor-acceptor blend so that charges separate cleanly, and engineering the frontier orbital energies of the molecules to minimize the energetic offset at the interface. The new work adds a third, distinctly photophysical lever. By deliberately engineering a thermally accessible bridge between dark charge-transfer states and bright localized states, and by supplying a luminescent sink that gives those excitons somewhere to go, the researchers effectively convert a loss channel into a radiative one. The same principle of charge-transfer to localized-state coupling has been discussed theoretically, notably in work on hybridized exciton states, but demonstrating it with a practical guest-acceptor additive in a record-efficiency device is a significant step from theory to technology.

There are, of course, questions that will shape the next phase of this research. The guest acceptor strategy was demonstrated in one particular host system, and extending it to other donor-acceptor pairs will require careful matching of the localized excited state energy to each interface. Long-term operational stability, always a central concern for organic photovoltaics, will need to be verified for the ternary blends. And the mechanism itself, involving thermal repopulation of higher-energy states, invites scrutiny of whether the small energetic penalty involved costs anything in photocurrent at different operating temperatures. Still, the combination of certified efficiency, spectroscopic evidence and molecular simulation presented in the study makes a compelling case that solid-state luminescence can be harnessed as a design tool. If the approach generalizes, the path from twenty-one percent toward the Shockley-Queisser-inspired limits of organic photovoltaics may run not through new absorbers alone, but through molecules engineered to glow.

Subject of Research: Suppression of non-radiative recombination in organic solar cells using solid-state emissive acceptors

Article Title: Solid-state emissive acceptors enable thermally accessible radiative pathways for efficient organic solar cells

Article References: Zhang, Y., Han, F., Zhou, R., Deng, Z., Fu, J., Rong, M., Ng, H. M., Fu, Y., Ding, X., Zeng, X., Yi, J., Xia, H., Lai, J. Y. L., Ma, R., Li, C., Lu, X., Yu, J., Zhu, H., Liu, J., … Pun, S. H. (2026). Solid-state emissive acceptors enable thermally accessible radiative pathways for efficient organic solar cells. Nature Photonics. https://doi.org/10.1038/s41566-026-02009-8

Image Credits: AI Generated

DOI: 10.1038/s41566-026-02009-8

Keywords: organic solar cells, non-fullerene acceptors, non-radiative recombination, charge-transfer states, electroluminescence, open-circuit voltage, ternary blend, photophysics, energy loss, power conversion efficiency, resonance energy transfer, Nature Photonics

To understand why these numbers matter, it helps to recall what happens inside an OLED. When electrons and holes recombine in the emissive layer, they form excitons, bound electron-hole pairs. Statistically, one quarter of these are singlet excitons and three quarters are triplets. Fluorescent emitters can only use the singlets, capping efficiency at 25 percent, while phosphorescent and thermally activated delayed fluorescence (TADF) emitters can, in principle, harvest all of them. But in deep-blue devices, where the emitter energy gap is large and the molecules are chemically fragile, the triplet population tends to linger. Slow-moving triplets collide with one another and with singlets, annihilating them in processes such as triplet-triplet annihilation and singlet-polaron annihilation. The result is efficiency roll-off, the loss of efficiency at high brightness, and accelerated molecular degradation that shortens device lifetime.

The central insight of the new work is that efficiently harnessing all electrically generated excitons on a sufficiently fast timescale is essential for deep-blue OLEDs to attain high efficiency, low roll-off and long operational lifetimes, and that this had constituted a long-standing challenge. The team, led by Dongdong Zhang and Lian Duan at Tsinghua, with Hugo Bronstein and Richard Friend’s groups contributing at Cambridge, built their device around a dual-sensitizer emission system that enables multiple synergistic sensitization processes. Together these pathways achieve near-unity exciton utilization on a submicrosecond timescale, dramatically shrinking the window in which destructive exciton collisions can occur.

The heart of the system is a blue TADF sensitizing host with a C3-symmetric triple donor-acceptor motif, a molecular architecture in which three donor-acceptor arms radiate from a central core. This symmetry creates what the authors describe as a cumulative effect from near-degenerate states, meaning several excited states sit at very similar energies and can cooperate rather than compete. The consequence is a break in a conventional trade-off that has constrained TADF design for a decade: fast singlet radiation and efficient triplet upconversion, the reverse intersystem crossing that recycles triplets into emissive singlets, have usually pulled molecular design in opposite directions. Fast radiative decay demands a large oscillator strength, while efficient upconversion demands a small singlet-triplet energy gap and strong spin-orbit coupling between the states. The near-degenerate states of the C3-symmetric molecule deliver both at once.

The emission architecture follows the logic of phosphor-assisted TADF-sensitized fluorescence, sometimes called hyperfluorescence. Instead of letting the narrowband terminal emitter handle exciton formation directly, the device delegates that job to the sensitizing host and the TADF sensitizer, which rapidly convert all four exciton spin species into singlet energy. That energy is then transferred to a narrowband fluorescent emitter, which does the actual light emission. The division of labor is crucial: the terminal emitter keeps its intrinsic narrowband emission, producing pure deep-blue color with a chromaticity y-coordinate of 0.10 and a full width at half maximum of just 15.4 nanometers, while the sensitizers handle the messy, fast exciton dynamics that would otherwise overwhelm a fragile blue emitter.

The performance figures place the device among the best deep-blue OLEDs reported to date. A maximum external quantum efficiency of 35.9 percent approaches the theoretical ceiling for a forward-emitting device, and the retention of 90 percent of that efficiency at 297.0 milliamperes per square centimeter is particularly striking. Most OLEDs, including many high-performing blue designs, lose a substantial fraction of their efficiency well before reaching such current densities, which correspond to the brightness levels demanded by high-definition displays and potential lighting applications. The LT80 lifetime of 632 hours, the time for luminance to fall to 80 percent of its initial 1,000-candela-per-square-meter value, represents a meaningful advance for a device combining this color purity, efficiency, and brightness.

Exciton dynamics studies underpinning the work reveal why the architecture succeeds. By tracking the kinetics of the excited states, the researchers showed that the multiple sensitization pathways operate on a dominant submicrosecond timescale, and that this speed substantially suppresses exciton annihilation. Annihilation processes are bimolecular: their rate scales with the square of the exciton density multiplied by the time excitons spend in the film. Cutting the exciton lifetime from microseconds to submicroseconds therefore cuts the annihilation probability disproportionately, allowing the device to hold its efficiency as current density climbs and to spare the organic molecules the energetic collisions that break chemical bonds and create non-radiative defects.

The study situates itself within a broader, decade-long campaign to solve what researchers have candidly called the blue problem. Earlier strategies include phosphorescent iridium and platinum emitters, polariton-enhanced Purcell effects that accelerate spontaneous emission, perdeuterated TADF molecules that resist chemical degradation, and various sensitized-fluorescence schemes that borrow the triplet-harvesting ability of a sensitizer to pump a stable fluorescent emitter. Each approach has chipped away at the trade-off between efficiency, color purity, and lifetime, but the combination of all three in a single deep-blue device has remained elusive. The new work’s contribution is to show that the timescale of exciton management, rather than any single material property, is the unifying variable that ties these performance metrics together.

The molecular design also benefited from careful computational and structural characterization. The researchers deposited the crystallographic coordinates of their C3-symmetric molecule with the Cambridge Crystallographic Data Centre, and their simulations of exciton dynamics, combined with energy-transfer analysis, allowed them to disentangle the contributions of the individual sensitization channels. This level of mechanistic detail matters for the field because it converts an empirical device result into a transferable design principle: build sensitizing systems whose excited states are near-degenerate and whose upconversion and radiative rates are both fast, and the annihilation problem that plagues deep-blue OLEDs largely takes care of itself.

For the display industry, the implications are tangible. Deep-blue pixels with y-coordinate near 0.10 and narrow spectral width are precisely what ultrahigh-definition standards demand, and a device that maintains near-peak efficiency at hundreds of milliamperes per square centimeter could reduce the power budget and thermal load of high-brightness panels. The remaining gap to commercial deployment, particularly the further lifetime extension needed for consumer products, is still substantial, but the demonstration that near-unity, submicrosecond exciton utilization can simultaneously deliver efficiency, color purity, and stability marks a clear step forward. It suggests that the path to durable blue OLEDs runs not through any single miracle molecule, but through the coordinated choreography of excitons on the fastest possible clock.

Subject of Research: Deep-blue organic light-emitting diodes with accelerated exciton utilization via dual-sensitizer emission systems

Article Title: Stable deep-blue organic light-emitting diodes with reduced efficiency roll-off via accelerated exciton utilization

Article References: Huang, T., Zhang, H., Wang, Q., Li, B., Mai, M., Xiao, Y., Bronstein, H., Friend, R., Duan, L., & Zhang, D. (2026). Stable deep-blue organic light-emitting diodes with reduced efficiency roll-off via accelerated exciton utilization. Nature Photonics. https://doi.org/10.1038/s41566-026-02029-4

Image Credits: AI Generated

DOI: 10.1038/s41566-026-02029-4

Keywords: OLED, deep-blue emission, TADF, exciton dynamics, efficiency roll-off, sensitized fluorescence, external quantum efficiency, device lifetime, Nature Photonics, display technology, triplet harvesting, narrowband emitter

To understand why the result matters, it helps to look closely at the architecture of an inverted perovskite solar cell. In this configuration, light enters through a transparent electrode and first encounters a hole-selective layer that extracts positive charge carriers from the perovskite absorber. In state-of-the-art devices, that layer is typically a self-assembled monolayer: a single molecular layer in which each molecule anchors to the oxide substrate through a phosphonic acid group and presents an energy-aligned frontier orbital to the perovskite above. These monolayers use vanishingly small amounts of material, coat rough surfaces uniformly, and have been central to the efficiency surge of recent years. But they carry a structural vulnerability. A monolayer built from a single molecular species tends to pack into one dominant motif, and when that motif is stressed, by heat, by mechanical strain, or by the chemical pressure of the perovskite crystallizing on top of it, the packing can collapse. When the packing collapses, the pathways that holes use to hop from the perovskite into the electrode are disrupted, and the device begins to degrade.

The Hong Kong-led team, including co-first authors Deng Wang, Mingqian Chen and Jiacong Feng, attacked this vulnerability by mixing three carbazole-naphthalene self-assembled molecules that share similar chemical skeletons but differ in their intermolecular interactions and packing preferences. The strategy mirrors the high-entropy concept that transformed alloy design, where mixing multiple elements in near-equimolar ratios stabilizes materials through configurational entropy rather than through a single dominant crystal structure. Here, the entropy is not in atomic positions but in packing modes. Because each of the three molecules prefers a slightly different way of stacking against its neighbors, the blended film cannot settle into one brittle, long-range-ordered arrangement. Instead, it forms a dense mosaic of coexisting packing motifs, a high-entropy system in which no single failure mode can propagate easily. The result is a contact that extracts holes efficiently while remaining remarkably resilient under external stress.

Proving that such a high-entropy molecular contact actually forms, rather than simply producing a phase-separated mess, required a battery of complementary techniques. Single-crystal analysis of the individual molecules revealed the distinct intermolecular interactions, hydrogen bonding patterns and π-stacking geometries that each species brings to the blend. Molecular dynamics simulations, run on the blended films, showed how the three components interpenetrate and how the resulting diversity of local environments suppresses the large-scale structural rearrangements that plague single-component monolayers. Interfacial characterizations of the actual devices then confirmed that the mixed contact maintains intimate, robust contact with the perovskite layer. Together, these measurements painted a consistent picture: the ternary blend does not segregate or compete, it cooperates, producing an interface whose structural heterogeneity is precisely the source of its mechanical and thermal toughness.

The charge-transport consequences of that heterogeneity are subtle but favorable. In an idealized, perfectly ordered monolayer, holes move through well-defined electronic coupling pathways between adjacent molecules. Disorder might seem like the enemy of such transport, and in amorphous organic semiconductors it often is. But the high-entropy contact occupies a sweet spot: the three molecules are chemically similar enough that their energy levels remain aligned, so no deep traps are introduced, while their diverse packing modes create multiple, redundant percolation pathways for hole extraction. Transient absorption spectroscopy measurements on the devices supported this picture, showing efficient hole transfer at the contact. In effect, the team traded a single elegant highway for a dense network of smaller roads, and the network proved far harder to knock out. The approach also echoes recent work on high-entropy hybrid perovskites, in which disordered organic moieties within the perovskite lattice itself have been shown to enhance stability, suggesting a broader design principle spreading across the field.

The photovoltaic numbers place the devices at the very front of the inverted perovskite pack. The champion cell delivered a power conversion efficiency of 27.50 percent, and an independent certified steady-state efficiency of 27.31 percent was recorded, a figure that stands among the highest reported for single-junction perovskite devices and compares favorably with entries on established efficiency charts. Efficiency alone, however, has never been the bottleneck for perovskite commercialization; stability has. Here the high-entropy contact earned its keep. Under maximum power point tracking at 85 degrees Celsius in ambient air, a punishing accelerated-ageing protocol that combines thermal stress, continuous illumination and electrical bias, the devices retained essentially all of their initial efficiency after 1,300 hours. The team also reported extended stability under a range of other accelerated ageing tests, consistent with the consensus ISOS procedures that the perovskite community uses to standardize stability reporting.

That combination of certified efficiency and heat tolerance addresses the two criteria that investors and module manufacturers scrutinize most closely. Perovskite modules must survive decades of outdoor service, during which rooftop temperatures can exceed 70 degrees Celsius in summer and internal junctions run hotter still. A contact layer that structurally collapses under such thermal load becomes a device-wide liability, initiating delamination and accelerating the decomposition of the perovskite itself. By hardening the molecular interface at its weakest scale, the single molecular layer, the high-entropy strategy protects the entire stack. The fact that the improvement required no exotic materials, only a ternary blend of closely related carbazole-based molecules that can be deposited from solution, makes the approach attractive for scalable manufacturing, where process simplicity and material cost weigh as heavily as laboratory performance.

The authors emphasize that the framework is broadly applicable beyond the specific molecules they synthesized. The underlying principle, that blending species with similar electronic structures but distinct packing motifs generates entropy-stabilized interfaces, could in principle be applied to electron-selective contacts, to the buried interfaces of tandem devices, and to other solution-processed thin-film technologies that rely on self-assembled monolayers, including organic electronics and emerging tandem architectures that pair perovskites with silicon. Recent parallel reports of ternary self-assembled molecular contacts for perovskite-silicon tandems and of entropy-regulating molecular locks that stabilize the perovskite lattice indicate that high-entropy thinking is rapidly spreading through molecular-level photovoltaic engineering. The present work adds a rigorous structural and mechanistic foundation to that trend, linking single-crystal chemistry, molecular simulation and device-level certification in a single coherent study.

Challenges remain before high-entropy contacts reach the factory floor. The long-term behavior of ternary blends over years rather than months, their behavior in full-size modules with large areas and interconnects, and the reproducibility of blend stoichiometry in industrial coating processes will all need to be demonstrated. Yet the conceptual shift is hard to overstate. For years, interfacial engineering in perovskite solar cells has pursued purity and order, one molecule, one packing mode, one optimized monolayer. This study demonstrates that controlled multiplicity can outperform perfection, converting the very disorder that engineers once feared into a shield against degradation. If the high-entropy design rule generalizes as broadly as the authors suggest, the molecular interfaces of future solar cells may look less like crystalline lattices and more like entropy-toughened mosaics, quietly extracting charge under a blazing sun for decades without complaint.

Subject of Research: High-entropy molecular hole-selective contacts for efficient and stable inverted perovskite solar cells

Article Title: High-entropy molecular contacts enable high-efficiency and stable perovskite solar cells

Article References: Wang, D., Chen, M., Feng, J., Li, Q., Wong, C.-T., Lei, G., Jiang, Q., Wang, T., Jiang, W., & Jen, A. K.-Y. (2026). High-entropy molecular contacts enable high-efficiency and stable perovskite solar cells. Nature Photonics. https://doi.org/10.1038/s41566-026-02028-5

Image Credits: AI Generated

DOI: 10.1038/s41566-026-02028-5

Keywords: perovskite solar cells, self-assembled monolayers, high-entropy materials, hole-selective contacts, power conversion efficiency, operational stability, molecular packing, inverted architecture, charge transport, molecular dynamics simulations, thermal ageing, Nature Photonics

The distortion in question is known as differential mode delay, or DMD. Because each mode follows a different path through the fiber, a pulse of light launched into all modes simultaneously arrives at the far end smeared across time, with the earliest and latest components separated by hundreds of nanoseconds on long-haul links. Separating the interleaved data streams requires multiple-input multiple-output digital signal processing, MIMO-DSP, whose computational burden scales as the product of the square of the number of modes and the width of the dispersion window. For long-distance transmission, that scaling quickly becomes impractical, demanding enormous digital equalizers that consume power, silicon area and money. Previous attempts to soften the blow relied on fixed mode scramblers or static mode permutations, but these passive tricks offer limited flexibility, require laborious trial-and-error tuning, and cannot adapt as fiber conditions change or as the number of modes grows.

Now a team of researchers at NTT in Japan has demonstrated a fundamentally different way of attacking the problem, reported in Nature Photonics. Instead of accepting the fiber’s transmission matrix as fixed and compensating for the damage entirely in the digital domain, they installed programmable photonic unitary processors at intermediate nodes along the transmission line. These processors directly reshape the optical signals in flight, optimizing the transmission channel itself rather than merely cleaning up after it. The team calls the scheme parameterized SDM transmission, and in a proof-of-concept experiment they used it to carry high-quality data over 1,300 kilometers of three-mode fiber, a distance at which conventional approaches would face crushing digital processing loads.

The heart of the demonstration is a telecom-grade programmable photonic processor built on a silica-based planar lightwave circuit platform. The chip implements an 8-by-8 Clements-type mesh of Mach-Zehnder interferometers, measuring 50 by 25 millimeters, and performs a unitary transformation on the spatial modes passing through it. Crucially, the device was engineered to meet the harsh requirements of real optical networks: it achieves a fiber-to-fiber insertion loss of just 2.1 decibels, operates across the entire telecom C band, works identically for both polarizations, and maintains a matrix fidelity above 96 percent across the full band. Those figures stand in sharp contrast to typical photonic processors, which often suffer more than 10 decibels of loss and function only at a single wavelength, making them useless for wavelength-division-multiplexed traffic.

Finding the right unitary transformation to apply at each node is itself a formidable mathematical challenge, and this is where the team’s second innovation comes in. They built a differentiable model of the entire SDM transmission system, essentially a digital twin in which every step of computing the accumulated modal dispersion, including the singular value decomposition used to extract group delays, is expressed in differentiable linear algebra. That property allows gradient-based optimization, the same backpropagation machinery that powers modern machine learning, to systematically tune the phase parameters of the interferometer mesh and drive the differential mode delay toward its minimum. Once the optimal unitary matrix is found in the digital twin, it is transferred to the physical photonic circuit at each transmission span.

Numerical simulations revealed how the approach behaves under different physical conditions. In fibers with no or weak intermodal coupling, the optimized unitary transformations suppressed the accumulation of modal dispersion far better than random mode mixing, which merely slows dispersion growth to a square-root-of-distance scaling. In strongly coupled fibers, the simulations showed, no effective unitary conversion exists and the optimization converges toward the random-mixing behavior, an honest boundary of the method. The team also found that deploying the processors more densely along the route further reduces the residual dispersion, and that the optimization landscape contains multiple equivalent minima, with the gradient-based search reliably finding whichever optimum lies nearest to its starting point.

The experimental system circulated 12-gigabaud polarization-multiplexed quadrature-phase-shift-keying signals through a recirculating loop containing 51.2 kilometers of graded-index three-mode fiber per span. Including the fiber loss, the mode multiplexers and the photonic processor, each span imposed about 17.4 decibels of total insertion loss, which was compensated by erbium-doped fiber amplifiers, meaning the processor slots naturally into existing amplifier-based link budgets. By sweeping a rotation angle that continuously morphs the applied matrix from the identity to a mode permutation, the researchers showed that the in-line optical processor exerts direct, predictable control over the accumulated modal delay, with experimental measurements tracking the digital twin’s predictions closely.

When the optimized unitary matrix was loaded onto the chip, the accumulated differential mode delay over the full link dropped from roughly 25 nanoseconds to about 10 nanoseconds across three representative wavelengths spanning the C band, confirming wideband, high-fidelity operation. Because the dispersion window sets the required length of the digital MIMO equalizer, that reduction translates directly into lower post-processing complexity. After 1,331 kilometers of transmission, the normalized generalized mutual information of every spatial and polarization mode remained comfortably above the 0.836 error-free threshold, with cleanly clustered constellations demonstrating that the low-loss, polarization-insensitive processor had preserved signal quality end to end.

The researchers also weighed the energy economics of their approach. Their current thermo-optic prototype draws roughly 6.4 watts for a full 8-by-8 mesh, but a three-stage multiplane-light-conversion design with optimized thermal isolation could bring that down to about 1 watt, in line with the budget of typical network nodes that consume tens of watts. Measured as energy per multiply-accumulate operation, the optimized design would achieve around 9.6 femtojoules, with silicon or silicon-nitride platforms potentially reaching below 2 femtojoules, two to three orders of magnitude better than state-of-the-art electronic processors performing equivalent matrix operations. If fiber characteristics never change, the optimized transformation could even be frozen into a passive circuit requiring zero standby power.

The implications reach beyond a single laboratory demonstration. The optimization framework is not tied to compensating modal delay alone; the same differentiable model can be extended to target mode-dependent loss, another chronic limiter of long-haul multimode transmission, potentially minimizing digital cost and maximizing capacity simultaneously. Unused ports in the interferometer mesh could be repurposed as an optical switching engine, letting a single device serve as both transmission optimizer and router. While further loss reduction, toward roughly 1 decibel or below, will be needed for longer distances and higher mode counts, the work establishes a scalable blueprint for embedding photonic computation directly into the optical layer, hinting at networks where the fiber plant itself becomes a programmable, self-optimizing machine.

Subject of Research: Programmable photonic unitary processors for modal dispersion compensation in long-haul spatial division multiplexed fiber transmission

Article Title: Programmable photonic unitary processor enables parameterized differentiable long-haul spatial division multiplexed transmission

Article References: Nakajima, M., Shibahara, K., Ikeda, K., Kawai, A., Notomi, M., Miyamoto, Y., & Hashimoto, T. (2026). Programmable photonic unitary processor enables parameterized differentiable long-haul spatial division multiplexed transmission. Nature Photonics, 20(10), 1193-1204. https://doi.org/10.1038/s41566-026-01997-x

Image Credits: AI Generated

DOI: 10.1038/s41566-026-01997-x

Keywords: spatial division multiplexing, photonic unitary processor, differential mode delay, multimode fiber, MIMO digital signal processing, planar lightwave circuit, Mach-Zehnder interferometer, gradient-based optimization, differentiable model, optical communications, wavelength division multiplexing, Nature Photonics

The achievement, led by Yu Guo and Yubo Wang in Hong X. Tang’s laboratory in Yale’s Department of Electrical Engineering, rests on an architectural insight borrowed from high-power laser engineering: the master-oscillator-power-amplifier, or MOPA, design. In a MOPA system, a small, exquisitely stable seed laser generates the optical signal, and separate amplifier stages then boost that signal to useful power levels without degrading its spectral purity or noise characteristics. This division of labour is what allows industrial Nd:YAG systems to be simultaneously precise and powerful. Reproducing that architecture on a chip, however, demanded that the researchers solve two problems that have long stymied integrated solid-state photonics: how to make a chip-scale Nd:YAG oscillator that can actually start lasing with modest pump power, and how to build waveguide amplifiers with enough gain to be useful.

The seed oscillator is the quieter triumph of the work. The team fabricated a microring resonator — a tiny circular waveguide that traps light as it circulates — directly in neodymium-doped YAG. The device operates in a double-resonant configuration, meaning that both the pump light and the lasing light are simultaneously resonant with the ring, dramatically enhancing the light-matter interaction at both wavelengths. The result is a laser threshold of just 2.9 microwatts of absorbed pump power, an extraordinarily low figure for a solid-state laser. For comparison, conventional diode-pumped Nd:YAG lasers typically require orders of magnitude more pump power before they begin to oscillate. This low threshold matters because it means the seed can be driven gently, preserving the narrow linewidth and low noise that make solid-state lasers so valuable, while leaving the task of power generation to the amplifiers downstream.

Those amplifiers form the second half of the system. When optimized as standalone devices, the single-pass neodymium-doped waveguide amplifiers demonstrated up to 46.6 decibels of small-signal gain — a factor of nearly 46,000 in optical power. Achieving such gain in a rare-earth-doped waveguide is notoriously difficult: the ions must be pumped efficiently, the waveguide must confine both pump and signal over a sufficient interaction length, and parasitic losses and unwanted lasing must be suppressed. The Yale team’s amplifiers also achieved a photon conversion efficiency of up to 53.2 percent under large-signal conditions, meaning that more than half of the pump photons arriving at the chip were converted into signal photons — a figure that approaches the performance of much larger bulk solid-state amplifiers and reflects careful engineering of the pump geometry and waveguide design.

When the low-threshold microring seed was combined with cascaded waveguide amplifiers on the microchip platform, the complete integrated MOPA system delivered more than 12 dBm of amplified continuous-wave output. That power level, while modest compared with industrial Nd:YAG lasers that produce tens of watts, is significant in the context of integrated photonics, where on-chip laser sources frequently struggle to produce even a few milliwatts of usable light. More importantly, the architecture is inherently scalable: additional amplifier stages can be cascaded, and the design principles established here — efficient pump utilization, low-threshold oscillation, and high-gain single-pass amplification — provide a roadmap for pushing chip-scale solid-state lasers toward watt-class output in future iterations.

The significance of this work becomes clearer when viewed against the broader landscape of integrated photonics. Most chip-scale lasers today rely on semiconductor gain media, such as indium phosphide or III-V compounds bonded to silicon, or on nonlinear conversion processes in materials like lithium niobate. These approaches excel in certain regimes but struggle to reach the exceptional spectral purity, efficiency, and wavelength coverage that diode-pumped solid-state lasers offer. Rare-earth-doped crystals such as Nd:YAG occupy a special niche: their narrow emission lines produce highly coherent light, their four-level energy structure enables efficient operation, and their emission wavelengths — including 1064 nanometres and harmonics at 532, 355, and 266 nanometres — are inaccessible to ordinary semiconductor diodes. Bringing this gain medium onto a wafer-scale, lithographically defined platform means the precision of solid-state lasers can finally be married with the manufacturability of chips.

The potential applications span an impressive range of fields. In quantum information science, trapped-ion quantum computers require multiple precisely controlled laser beams at specific wavelengths to cool and manipulate individual qubits; integrated Nd:YAG sources could replace the laboratory-scale laser systems that currently make such machines enormous and fragile. In coherent optical communications, stable narrow-linewidth lasers at 1064 nanometres and nearby bands serve as local oscillators and carriers. In precision metrology, optical clocks and interferometric sensors demand exactly the combination of low noise and high power that the MOPA architecture provides. Even nonlinear photonics stands to benefit, since efficient frequency conversion and frequency-comb generation in on-chip resonators require pump lasers with both adequate power and exceptional coherence — precisely what this integrated system is designed to deliver.

The path to this result also reflects a broader trend in the Tang group’s research programme, which has previously demonstrated photonic-integrated titanium:sapphire lasers by diffusing dopants into sapphire substrates and building low-loss waveguides on top. The same philosophy — take a proven bulk gain medium, engineer a low-loss photonic platform around it, and apply system-level architectures from laser engineering — has now been extended to neodymium-doped garnets. The fabrication relies on wafer-scale processing techniques, and the authors note that the underlying substrate platform, a heterogeneous sapphire-supported low-loss photonic system, was developed in their earlier work. This lineage suggests that the Nd:YAG MOPA is not an isolated demonstration but part of a maturing toolkit for building solid-state photonic integrated circuits, with data and code from the study made publicly available through Zenodo to support reproducibility.

Challenges remain before chip-scale Nd:YAG lasers can displace their benchtop ancestors. Output power must climb by another two to three orders of magnitude to compete in industrial materials processing, thermal management on chip becomes increasingly demanding at higher pump powers, and the pump lasers themselves — currently off-chip diode sources — would ideally be integrated or fibre-coupled with minimal loss. Nevertheless, the demonstration of a complete master-oscillator-power-amplifier system in which every functional element, from the 2.9-microwatt-threshold seed to the 46.6-decibel-gain amplifiers, operates on a single microchip platform marks a genuine milestone. It transforms Nd:YAG from a symbol of photonics’ macroscopic past into a building block for its integrated future, and it signals that the most trusted laser crystal in science may soon be etched, by the millions, onto silicon wafers.

Subject of Research: An integrated photonic Nd:YAG laser-amplifier system using a microchip master-oscillator-power-amplifier architecture

Article Title: Microchip Nd:YAG laser with master-oscillator–power-amplifier architecture

Article References: Guo, Y., Wang, Y., Zhao, H., Yang, F., Yang, G., Xie, H., & Tang, H. X. (2026). Microchip Nd:YAG laser with master-oscillator–power-amplifier architecture. Nature Photonics. https://doi.org/10.1038/s41566-026-01984-2

Image Credits: AI Generated

DOI: 10.1038/s41566-026-01984-2

Keywords: Nd:YAG laser, integrated photonics, master-oscillator power-amplifier, microring resonator, waveguide amplifier, solid-state lasers, rare-earth doping, photonic integrated circuits, laser threshold, coherent light sources, Yale University, Nature Photonics

The achievement rests on a technique that has become one of the most powerful control knobs in attosecond science: two-colour waveform synthesis. Instead of hitting the tunnel junction with a single laser beam, the researchers combined two coherent light fields of different colours, a fundamental frequency and its second harmonic. When these two fields overlap, their sum is no longer a simple sinusoidal oscillation. Within each optical cycle, the combined electric field becomes an asymmetric waveform, with a strong half-cycle in one direction and a weaker, differently shaped excursion in the other. For an electron contemplating a quantum jump across the tunnel barrier, that asymmetry matters enormously. The instantaneous field tilts the barrier, lowers it on one side, and determines the precise instant, within the optical cycle, when tunnelling is most probable. By adjusting the relative phase between the two colours, the team could shift that favoured instant back and forth, and with it, flip the direction of the resulting current pulse.

What makes the result remarkable is the combination of timescale and spatial precision. The junction in a scanning tunnelling microscope is a few nanometres or less across, and the tunnelling process itself is confined to a region far smaller than that. The researchers demonstrated sub-ångström topographic sensitivity, meaning the laser-driven current responded to height changes on the surface at the level of individual atoms, while achieving a lateral spatial resolution of two nanometres. In other words, the attosecond current they generated and steered remained a genuinely microscopic probe, not a diffuse photoresponse smeared across the sample. And they did it under ambient conditions, at room temperature and in air, rather than in the cryogenic vacuum that most ultrafast microscopy experiments demand.

A persistent obstacle in laser-driven STM has been heat. When laser light strikes the tip or the sample, some of its energy is inevitably absorbed, raising the temperature of the junction and producing thermal expansion of the tip, thermally assisted currents and other artefacts that can masquerade as genuine ultrafast dynamics. Earlier femtosecond and picosecond experiments in laser-assisted STM were often haunted by exactly this problem, and distinguishing a true sub-cycle electronic response from a slow thermal signal became a central methodological challenge for the field. The Technion team addressed this directly. Because their current control depends on the sub-cycle waveform of the two-colour field, flipping the carrier-envelope phase flips the current direction, whereas a thermal effect would be completely indifferent to the sign of the electric field. The observed phase-dependent, direction-reversing current is therefore an unambiguous signature of coherent, lightwave-driven electron transport, and the experiment was explicitly designed to be free of thermal artefacts.

To understand the mechanism, the researchers turned to theory at two levels of description. On the one-electron side, they employed a strong-field model of tunnelling, in the spirit of the Keldysh framework that has underpinned strong-field physics since 1965, treating the electron as a wavepacket launched through a field-tilted barrier. On the many-body side, collaborators performed time-dependent density functional theory calculations of the full metal-insulator-metal junction, capturing the collective response of the electrons in the electrodes. Projecting the experimental data onto both theoretical descriptions revealed a consistent physical picture: a three-step transport process operating in the non-adiabatic tunnelling regime. In this regime, the optical field changes so quickly that the electron cannot follow it adiabatically; instead, the field launches the electron into the barrier, the wavepacket propagates across the gap while the field continues to evolve, and the electron is finally collected on the far side, with the whole sequence compressed into a fraction of an optical cycle.

From their theoretical analysis, the team extracted a concrete number for the duration of the current burst: 860 attoseconds. That figure, less than a single femtosecond, quantifies how briefly the electrons stream through the junction during each pulse. It also places the experiment firmly in the lightwave electronics regime, where the oscillating carrier wave of light, rather than a sequence of electronic switches, dictates the timing of current flow. Lightwave electronics has been advancing rapidly in recent years, with petahertz-scale field control demonstrated in nanotips, nanoantennas and solid-state devices, but the STM junction offers something none of those platforms can: the ability to position the driven current with atomic-scale precision on a surface and, in principle, to image ultrafast charge dynamics as they unfold at specific sites, such as a single molecule or a defect.

The lineage of this work runs through several landmark experiments. Attosecond science itself was born from the recognition that strong laser fields can ionize atoms within a fraction of an optical cycle, and that the emitted electrons carry timing information about that process. In 2011, researchers at the Max Planck Institute of Quantum Optics showed attosecond control of electrons emitted from a nanoscale metal tip, extending strong-field physics to nanostructures. Later experiments traced attosecond electron emission from tungsten nanotips and demonstrated attosecond field emission from nanotips driven by terahertz-scale waveforms. In parallel, ultrafast STM developed along its own track, first with pulsed lasers that suffered from thermal complications, then with single-cycle terahertz pulses that enabled femtosecond imaging of molecular motion, and more recently with all-optical sub-cycle microscopy on atomic length scales. The new work synthesizes these threads, bringing waveform-level attosecond control, the hallmark of gas-phase strong-field physics, into the spatially resolved world of the STM.

The two-colour approach itself has a distinguished history. Phase-controlled ionization with two colours was explored in atoms in the 1990s, and coherent control of above-threshold photoemission from tungsten nanotips followed in 2016. What the Technion team added was the junction geometry and the diagnostic power of the STM platform. In a tunnel junction, the current direction is a measurable, meaningful quantity: electrons can flow from tip to sample or from sample to tip, and the net laser-induced current reflects the asymmetry of the driving waveform. By scanning the two-colour phase and recording how the current reverses, the researchers effectively performed attosecond streaking inside the junction, using the optical waveform itself as the clock that timestamps the tunnelling event.

The practical implications reach toward a long-sought goal: triggering and imaging ultrafast charge dynamics at specific locations on a surface. Many of the most important processes in chemistry, materials science and nanotechnology, from charge transfer in molecular junctions to carrier dynamics in photovoltaic materials, begin with electron motion on attosecond to femtosecond timescales localized to nanometre-scale regions. A microscope that can launch a directional attosecond current pulse at a chosen point and then read out the response could watch those processes unfold in real space and real time simultaneously. The two-nanometre lateral resolution and sub-ångström vertical sensitivity reported here, achieved under ambient conditions, suggest that such spatiotemporal microscopy need not be confined to specialized cryogenic laboratories.

There remain challenges to overcome before attosecond STM becomes a routine tool. The current bursts are generated by intense optical fields, and extending the technique to more delicate samples, to insulating substrates and to single-molecule junctions will require careful control of the near-field enhancement at the tip. The theoretical framework, spanning one-electron strong-field models and full many-body simulations, will need to keep pace as experiments move to more complex materials. But the conceptual barrier has now been crossed. Electrons tunnelling through the gap of a scanning tunnelling microscope have been caught in the act, timed to within a few hundred attoseconds, and steered at will by the waveform of light. The fastest event in electronics and the sharpest eye in microscopy are, at last, looking at the same thing at the same time.

Subject of Research: Attosecond control of laser-driven electron tunnelling currents in a scanning tunnelling microscope junction

Article Title: Attosecond current control and timing in a scanning tunnelling microscope

Article References: Davidovich, D., Ma, B., Goldner, A., Cohen, S., Chen, Z., Borisov, A. G., & Krüger, M. (2026). Attosecond current control and timing in a scanning tunnelling microscope. Nature Photonics. https://doi.org/10.1038/s41566-026-02021-y

Image Credits: AI Generated

DOI: 10.1038/s41566-026-02021-y

Keywords: attosecond science, scanning tunnelling microscopy, lightwave electronics, two-colour laser pulses, quantum tunnelling, ultrafast microscopy, strong-field physics, TDDFT, nanoscale junctions, carrier-envelope phase, electron transport, Nature Photonics

Writing in Nature Photonics, Jiaqi Liu and colleagues, working under the supervision of Guangda Niu of the Wuhan National Laboratory for Optoelectronics at Huazhong University of Science and Technology and Mengling Xia of the Wuhan University of Technology, describe a design strategy built on so-called zero-dimensional structured materials. In such crystals, the functional building blocks are isolated molecular units that do not share bonding directions with their neighbours in any crystallographic orientation. Because each unit is electronically self-contained, cutting or growing the crystal in any direction never leaves behind broken chemical bonds at the surface. The result is a semiconductor that is, in the researchers’ terminology, dangling-bond-free along all crystallographic directions.

The significance of this property becomes clear when one considers how defects arise in ordinary semiconductors. A conventional three-dimensional crystal, such as silicon, shares covalent bonds in every direction, so any grain boundary or surface necessarily terminates those bonds and creates dangling bonds, chemically unsatisfied sites that trap charge carriers and dissipate energy as heat rather than light. Two-dimensional materials such as transition-metal dichalcogenides avoid this problem within their atomically thin planes, but their edges remain problematic. One-dimensional wires solve the edge problem along their axis yet still expose discontinuities at their tips and side surfaces. Even the celebrated halide perovskites, which have revolutionized solar cells and radiation detectors with their remarkable defect tolerance, rely on passivation strategies to tame their interfacial defects rather than eliminating them structurally.

Zero-dimensional materials sidestep this entire problem, but until now they carried a penalty of their own. Because the functional units are electronically isolated, charge and energy transport within them tends to be isotropic, meaning that a crystal grows with similar rates in all directions and adopts compact, blocky morphologies. That isotropy is excellent for electronic performance but awkward for imaging, where the geometry of the scintillator film matters enormously. In X-ray scintillation imaging, light generated deep inside a thick film scatters as it travels to the detector, and lateral spreading degrades spatial resolution. Columnar structures, in which parallel rods act like optical fibres channeling light toward the detector, are the standard remedy, as demonstrated by the structured caesium iodide scintillators used commercially since the late 1990s. Achieving such columnar growth without sacrificing the defect-free electronic character of the material seemed impossible, because the two requirements pull in opposite directions.

The Chinese team’s insight was that the geometry of a crystal and the electronic dimensionality of its structure can be decoupled. To do so, they exploited a subtle chemical lever built into the uranyl ion, a linear O=U=O unit in which a uranium atom is flanked by two strongly bonded oxygen atoms. In the model compound caesium uranyl chloride, Cs2UO2Cl4, the uranium–oxygen double bonds are dramatically stronger and more directional than the uranium–chlorine bonds that link neighbouring uranyl groups. This bonding disparity means the crystal’s growth kinetics differ from one crystallographic direction to another, even though the uranyl units themselves remain electronically isolated. By tuning the balance between the fast-growing and slow-growing facets, the researchers drove the crystals to elongate into one-dimensional rods while preserving the zero-dimensional, dangling-bond-free electronic framework intact.

The concept draws on classical crystal-growth theory that dates back more than a century. In 1901, Georg Wulff proposed that the equilibrium shape of a crystal is determined by the relative surface energies of its facets, and Carl Herring’s theorems of 1951 formalized how surface free energy governs morphology. The team applied this thermodynamic framework to the chemically anisotropic uranyl system, using it to predict which facets would dominate the equilibrium rod shape. They then validated the prediction at the atomic scale with transmission electron microscopy, characterizing the crystal boundaries to confirm that the expected surfaces form and that no problematic bonding discontinuities appear. The work was a collaboration among the Wuhan University of Technology, Huazhong University of Science and Technology and Beijing University of Technology, with Wei Wang and Yue Lu contributing the atomic-scale electron microscopy characterization.

On the computational side, the researchers employed density functional theory calculations with the DFT-1/2 correction method, a technique developed to overcome the systematic underestimation of band gaps in conventional approximations to density functional theory. This allowed them to model the electronic structure of the material accurately enough to confirm that the anisotropic crystal growth does not compromise the isotropic, defect-free electronic properties that make zero-dimensional semiconductors attractive in the first place. The combination of thermodynamic growth modelling, atomic-resolution microscopy and corrected band-structure calculations gave the team confidence that their design principle is physically robust rather than a lucky accident of one particular compound.

The payoff came when the columnar Cs2UO2Cl4 crystals were tested as an X-ray scintillator. Uranyl compounds have attracted growing interest as scintillator materials since 2018, when researchers first highlighted uranium as a distinct metal centre for building intrinsic X-ray scintillators, with the heavy uranium nucleus providing strong X-ray absorption and the uranyl luminescence providing efficient light emission. Subsequent work explored uranium-organic frameworks and uranyl-cluster compounds for flexible and thermally adaptive scintillators, but spatial resolution remained limited by the film structures those materials formed. The new columnar geometry changes that picture decisively: the team’s Cs2UO2Cl4 scintillator achieved a spatial resolution of 34 line pairs per millimetre, a figure that places it among the highest-resolution scintillation imaging media reported and corresponds to the ability to distinguish features finer than fifteen micrometres across.

The practical implications extend across medical diagnostics, industrial inspection and scientific instrumentation. In clinical X-ray imaging and computed tomography, higher spatial resolution translates directly into the ability to visualize finer anatomical structures and subtler lesions at lower radiation doses, because fewer photons are wasted on scattered, blurred light. In industrial and security screening, fine-resolution scintillators enable detection of small defects or threats. The researchers also emphasize the generalizability of their approach: the underlying principle, that anisotropic chemical bonding can be introduced within a zero-dimensional framework to sculpt crystal geometry without disturbing electronic isotropy, is not limited to uranyl halides. Any material family containing chemically inequivalent bonds between electronically isolated units could, in principle, be engineered the same way, opening a route to defect-tolerant semiconductors with customizable shapes for light-emitting diodes, photodetectors and other optoelectronic devices where interfacial defects have long been the performance bottleneck.

The study, published on 25 September 2026 in Nature Photonics, arrives amid intense global competition to improve radiation detection materials, with halide perovskites and their derivatives dominating recent advances. What distinguishes this work is its conceptual reframing: rather than passivating defects after they form, the team designed them out of the material at the structural level, then recovered the anisotropic geometry needed for high-resolution imaging through chemistry rather than through growth tricks that would reintroduce broken bonds. The authors declare no competing interests, and the work was supported by the National Natural Science Foundation of China, the National Key Research and Development Program of China, the Beijing Natural Science Foundation, the Shenzhen Science and Technology Program and Huazhong University of Science and Technology. If the zero-dimensional design philosophy proves as transferable as the authors anticipate, the humble dangling bond, long the bane of semiconductor engineering, may finally lose its grip on the next generation of imaging technology.

Subject of Research: Dangling-bond-free zero-dimensional Cs2UO2Cl4 scintillators for ultrahigh-resolution X-ray imaging

Article Title: Dangling-bond-free, chemically anisotropic semiconductors for ultrahigh-resolution X-ray imaging

Article References: Liu, J., Liao, M., Liu, X., Ma, N., Li, H., Wang, W., Lu, Y., Xu, Y., Luo, G., Tang, J., Xia, M., & Niu, G. (2026). Dangling-bond-free, chemically anisotropic semiconductors for ultrahigh-resolution X-ray imaging. Nature Photonics. https://doi.org/10.1038/s41566-026-02013-y

Image Credits: AI Generated

DOI: 10.1038/s41566-026-02013-y

Keywords: X-ray imaging, scintillators, zero-dimensional materials, dangling bonds, Cs2UO2Cl4, uranyl halide, crystal growth, spatial resolution, defect tolerance, semiconductors, Nature Photonics, optoelectronics

The study, published in Nature Photonics, reports angle-resolved attosecond streaking measurements on helium and neon atoms, the pristine quantum systems that serve as the hydrogen atoms of attosecond physics. By recording not just the energies of photoelectrons kicked out by an extreme ultraviolet attosecond pulse, but also the full angular distribution of their emission directions, the team gained access to a quantity that conventional streaking discards entirely: the angular momentum content of the freed electron waves.

To appreciate why this matters, it helps to revisit how attosecond streaking works. A burst of extreme ultraviolet light, lasting mere hundreds of attoseconds, tears an electron from an atom. Almost simultaneously, a strong infrared laser field, the streaking field, acts on the liberated electron, shifting its final kinetic energy by an amount that depends on the vector potential of the light wave at the moment of ionization. Sweeping the delay between the two pulses maps out that vector potential, and with it the timing of photoemission itself. This is the scheme that underpinned the birth of attosecond metrology, celebrated in the 2001 measurement of light pulses shorter than a femtosecond, and it has since been used to clock tunneling delays and inner-shell processes with astonishing precision.

The classical reading of streaking treats the electron as a point charge absorbing a momentum kick from the field. But quantum mechanics insists that the electron, once free, is a superposition of partial waves, spherical wave components each labeled by a definite angular momentum quantum number. When the infrared field shakes the freshly ionized electron, it drives so-called continuum-continuum transitions, absorbing and emitting infrared photons while the electron remains unbound. These transitions redistribute population among the partial waves, and the resulting interference patterns encode themselves in the angular distribution of the detected electrons. Angle-resolved streaking, the team realized, is therefore not merely a timing measurement but a movie of angular momentum in motion.

The experimental apparatus combined intense attosecond pulses with a high-resolution velocity-map imaging spectrometer of the thick-lens design, capable of recording photoelectron momentum distributions with fine angular resolution. By scanning the delay between the attosecond pulse and the infrared streaking field in steps far finer than the optical cycle, the researchers assembled two-dimensional movies in which the photoelectron angular distributions visibly morph from one delay to the next. Measurements were performed on helium, whose simple two-electron structure makes theoretical treatment tractable, and on neon, which adds the complexity of multiple ionization channels, including contributions from both the 2p and 2s orbitals.

Theoretical support came from two independent computational frameworks. The team solved the time-dependent Schrödinger equation, the gold standard of strong-field theory, which tracks the full wavefunction of the atom and electron without approximation, and they also applied the strong-field approximation, a simplified model that treats ionization and subsequent field interaction in a controlled analytic limit. The agreement between experiment and the TDSE simulations was striking, and the SFA analysis provided the interpretive lens through which the measured angular distributions could be decomposed into their constituent partial waves and their time-dependent weights.

What the movies revealed is genuinely surprising. When the attosecond pulse ionizes the atom near the crest of the electric field of the infrared wave, the escaping electron populates a richer set of partial waves than when ionization occurs near the crest of the vector potential, a quarter cycle away. Since these two crests define the classical and quantum pictures of the light wave, the finding demonstrates that the quantum character of the interaction depends on precisely which feature of the field the electron encounters first. Moreover, the dominant interference mechanism switches character over the course of the streaking cycle: near one phase, partial waves of the same parity interfere, while at another, opposite-parity channels take over. Parity, the symmetry of a wavefunction under inversion of coordinates, is one of the most fundamental labels in atomic physics, and watching the interference regime flip between same- and opposite-parity contributions amounts to watching quantum symmetry bookkeeping play out in real time.

Equally striking is the strength of the multiphoton coupling the team uncovered. The infrared dressing field in a streaking experiment is comparatively gentle by strong-field standards, and one might expect the freed electron to exchange at most a single infrared photon in a perturbative handshake. Instead, the angular distributions show that substantial multiphoton continuum-continuum coupling persists even at weak infrared intensities, meaning the liberated electron absorbs and emits multiple infrared photons during its flight. The relevant interaction strength in the experiment was characterized by the dimensionless parameter gamma, defined as the product of the electron momentum, the peak vector potential, and the infrared frequency, which reached approximately 3.3 in the measurements, well into the regime where multiphoton dynamics flourish. This non-perturbative character has been latent in every streaking measurement ever performed, subtly shaping the very energy shifts researchers have been interpreting with quasi-classical formulas.

The implications ripple outward across attosecond science. Streaking underlies measurements of photoemission delays that probe electron correlation, Wigner-like time lags in atomic and molecular ionization, and the characterization of ever-shorter light pulses, including isolated attosecond and even attosecond-scale X-ray pulses from free-electron lasers. A quantum-state-resolved understanding of the streaking mechanism itself gives experimentalists a sharper tool for separating intrinsic atomic delays from measurement-induced ones, a distinction that has occupied the field since delays in photoemission were first clocked in helium in 2010. The results also connect to a broader frontier in which angular distributions of photoelectrons serve as reporters of wave-packet structure, from Fano resonance phase measurements to attosecond chronoscopy of electron vortices and chiral photoionization dynamics.

For a technique so mature, the discovery carries a certain humility: one of attosecond science’s most reliable instruments has been quietly performing quantum acrobatics all along. The team has made its experimental data publicly available through Zenodo, and the delay-resolved photoelectron movies of helium and neon are available as supplementary material, allowing anyone to watch partial waves rise and fall across an optical cycle. As attosecond physics pushes toward ever more complex targets, from molecules to surfaces to liquids, the lesson of this work is clear: the measuring light does not merely nudge electrons along classical trajectories, it reshapes their quantum identity, and only by reading the angular momentum of the liberated waves can the full story of ultrafast dynamics be told. The stopwatch, it turns out, has been keeping quantum time.

Subject of Research: Angle-resolved attosecond streaking of photoelectron angular momentum in helium and neon

Article Title: Attosecond streaking of photoelectron angular momentum

Article References: Gao, J., Liang, H., Hasan, M., Yuan, Y., Eisenhutt, Z., Tsai, M.-S., Chen, M.-C., & Han, M. (2026). Attosecond streaking of photoelectron angular momentum. Nature Photonics. https://doi.org/10.1038/s41566-026-02020-z

Image Credits: AI Generated

DOI: 10.1038/s41566-026-02020-z

Keywords: attosecond science, attosecond streaking, photoelectron angular distributions, angular momentum, continuum-continuum transitions, helium, neon, strong-field approximation, time-dependent Schrödinger equation, Nature Photonics, ultrafast photonics, multiphoton coupling