The central challenge addressed by the team concerns non-fullerene acceptors, or NFAs, the electron-accepting molecules that have driven the recent surge in organic photovoltaic performance. In a bulk heterojunction solar cell, a donor polymer and an acceptor molecule are blended together to form an interpenetrating network through which photogenerated charges must travel. For efficient charge generation and transport, the acceptor molecules need to pack into ordered, crystalline domains with close π-π stacking, the parallel overlap of their conjugated π-electron systems that facilitates electron delocalization. Yet excessive crystallinity can cause the acceptor to separate from the donor polymer, degrading the miscibility of the blend and producing a coarse, unstable morphology. Historically, molecular designs that pushed crystallinity upward tended to sacrifice blend compatibility, and designs that preserved compatibility tended to leave behind disordered packing and large nonradiative energy losses, the fraction of absorbed photon energy dissipated as heat rather than converted into charge.

The SUSTech group, led by corresponding author Professor Feng He, approached this dilemma through what the researchers describe as fine molecular engineering. Rather than redesigning the acceptor scaffold wholesale, the team made selective, targeted modifications to a parent molecule designated 7C-2F, which is built around a 1,4-diazahexane core. From this starting point, three new non-fullerene acceptors were synthesized by independently controlling two structural variables: the length of the side chains attached to the molecular framework and the degree of π-conjugation in the terminal groups, the electron-deficient end units that largely govern the optical and electronic properties of the acceptor. This modular approach allowed the researchers to isolate the effect of each structural change on molecular packing, blend morphology, and device behavior.

The first structural variable, side chain shortening, produced two acceptors named 7C-BO-2F and 7C-eC9-2F. The second variable, extension of the π-conjugation of the terminal groups, produced a third acceptor named 7C-N2F. Although these two strategies act on different parts of the molecule, the study found that both converge on the same set of physical outcomes. Each modification improved molecular crystallinity, meaning the acceptor molecules adopted more ordered solid-state packing, and each shortened the π-π stacking distance, the spacing between adjacent conjugated planes in the crystalline domains. Closer stacking strengthens electronic coupling between molecules, which promotes efficient charge transport. Critically, the enhanced order also suppressed nonradiative energy loss, the dominant remaining channel through which modern organic solar cells squander potential voltage.

The photovoltaic results underscore how consequential these fine structural adjustments proved to be. When the acceptor 7C-eC9-2F was paired with the donor polymer PM6 in a conventional bulk heterojunction device, the system achieved a power conversion efficiency of 19.67 percent, a figure that places it among the highest-performing organic photovoltaic systems reported. Equally significant is the energy loss of only 0.539 electron volts, a remarkably small value for an organic solar cell. Nonradiative losses arise when excited molecular states decay without emitting photons or generating charges, and suppressing them is widely regarded as the principal route to raising the efficiency ceiling of organic photovoltaics. The fact that the same molecular features that tighten crystalline packing also curtail these losses illustrates the internal coherence of the design strategy: efficiency gains and morphological improvements flow from a single, unified structural logic rather than from competing optimizations.

Stability, the perennial weak point of organic solar cells, is where the new acceptors distinguish themselves most decisively. Devices based on 7C-eC9-2F were subjected to two standard accelerated aging tests. Under continuous illumination, the time required for the device efficiency to fall to 80 percent of its initial value, a benchmark denoted T80, reached 2728 hours. When the devices were held at 65 degrees Celsius, a temperature representative of real-world rooftop operating conditions, the T80 value reached 1242 hours. In both tests, the 7C-eC9-2F devices significantly outperformed the control systems included in the study. The researchers attribute this durability to the optimized molecular aggregation states and the clear, well-defined microstructure of the active layer, which maintains its charge-generating and charge-transporting architecture even under sustained thermal and optical stress. In effect, the same crystallinity that boosts efficiency also anchors the morphology against the gradual coarsening that typically degrades organic photovoltaic devices over time.

The improved performance stems from a convergence of factors that the authors identify as the mechanistic foundation of the work. Sophisticated molecular engineering of the acceptors produced optimized aggregation states, improved crystallinity, suppressed nonradiative recombination, and a well-defined microstructure. These properties collectively promote efficient charge generation and transport while ensuring morphological durability. The balance between crystallinity and miscibility, often treated as an unavoidable compromise in acceptor design, is here resolved by structural tailoring so precise that both properties improve together. The side chain and terminal group modifications act on the molecular fine structure in ways that tighten packing within acceptor domains without provoking the macroscopic phase separation that would destroy blend compatibility, a result the researchers link directly to the simultaneous gains in efficiency and stability.

Beyond the bulk heterojunction architecture, the team also evaluated the new acceptors in quasi-planar heterojunction, or Q-PHJ, devices, an alternative fabrication geometry in which the donor and acceptor layers are deposited in a more layered arrangement rather than as a fully intermixed blend. The acceptors delivered excellent photovoltaic performance in this structure as well, demonstrating good fabrication adaptability. This cross-process applicability matters for practical manufacturing, because different deposition and annealing protocols impose different demands on material systems. An acceptor that performs well across multiple device architectures offers device engineers substantially more flexibility than one optimized for a single fabrication route, and the Q-PHJ results suggest that the benefits of the fine structural tailoring are intrinsic to the molecules themselves rather than dependent on any particular processing window.

The research was carried out by a team whose co-first authors are Dr. Mingpeng Li, Dr. Waqar Ali Memon, and postdoctoral fellow Xue Lai, all senior visiting scholars in the Department of Chemistry at SUSTech, with Professor Feng He serving as corresponding author. The work was supported by the National Natural Science Foundation of China and the Shenzhen Natural Science Foundation. The study was published on 11 September 2026 under the title Subtle Structural Tailoring Enables Improved Crystallinity and Miscibility for High-Efficiency, Stable Organic Photovoltaics, and the authors report no conflict of interest. The article is available as diamond open access, with no fees for authors or readers, consistent with the publishing model of CCS Chemistry.

The broader significance of the study lies in the design guidance it offers for the next generation of organic photovoltaic materials. By demonstrating that selective control of side chain length and terminal group conjugation can raise crystallinity, shorten π-π stacking distances, suppress nonradiative energy loss, and preserve blend miscibility all at once, the work provides a practical molecular blueprint for overcoming the efficiency-stability trade-off that has constrained the field. The performance of the PM6:7C-eC9-2F system, with its 19.67 percent efficiency, 0.539 electron volt energy loss, 2728-hour illumination T80, and 1242-hour thermal T80 at 65 degrees Celsius, constitutes a concrete benchmark for what fine molecular engineering can achieve. As organic photovoltaics move from laboratory curiosities toward commercial devices, strategies of this kind, which treat molecular fine structure as the primary lever for both efficiency and intrinsic stability, are likely to shape the material systems that carry the technology into practical deployment.

Subject of Research: Organic photovoltaic materials and molecular engineering

Article Title: Fine-structure regulation improves crystallinity and compatibility to achieve efficient and stable organic photovoltaics

Article References: Fine-structure regulation improves crystallinity and compatibility to achieve efficient and stable organic photovoltaics. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: organic photovoltaics, non-fullerene acceptors, molecular engineering, solar energy, CCS Chemistry, energy loss, device stability, bulk heterojunction, Fine-structure, regulation, improves, crystallinity

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

The quark–gluon plasma, or QGP, is a state of deconfined quarks and gluons produced in ultrarelativistic heavy-ion collisions. In the earliest instants of the collision, pairs of quarks and gluons undergo hard scatterings, producing high-momentum particles that fly outward. When the plasma is present, these energetic partons lose energy through collisional and radiative processes, a phenomenon known as jet quenching. Experiments at the Relativistic Heavy Ion Collider (RHIC) and the LHC have long observed a strong suppression of jets and high-momentum hadrons in central lead–lead and gold–gold collisions, and this suppression is one of the defining signatures of the plasma’s existence.

The challenge for experimentalists is establishing a reliable reference point. Jets are reconstructed from showers of particles, and the reconstruction itself can be biased by the very energy loss being studied. ALICE’s new measurement sidesteps this problem by exploiting electroweak particles, in this case direct-prompt photons, which are produced in the first instants of the collision and do not interact strongly with the QGP. At leading order in perturbative quantum chromodynamics, a prompt photon is produced back-to-back in azimuthal angle with a recoiling parton of similar transverse momentum. The photon therefore serves as an unmodified clock and energy scale for the hard scattering, while its partner parton plows through the plasma and emerges modified.

To isolate genuine prompt photons from a sea of background, ALICE applied an isolation criterion. Photons were required to carry transverse momenta between 18 and 40 GeV/c at midrapidity, and the sum of charged-particle transverse momenta within a small cone of angular radius 0.2 around the photon direction had to be below 1.5 GeV/c, after subtracting the estimated contribution of the underlying event. This tight selection suppresses fragmentation photons, bremsstrahlung photons, and photons from neutral-meson decays, which are typically accompanied by other particle fragments. The associated charged hadrons were measured with transverse momenta above 1.8 GeV/c using the Inner Tracking System and the Time Projection Chamber.

The analysis, based on lead–lead data collected in 2015 and 2018, examined three collision centrality classes: central (0–30%), semicentral (30–50%), and peripheral (50–90%). For each trigger photon, the researchers constructed the conditional yield D(zT) of associated hadrons, where zT is the ratio of the hadron’s transverse momentum to the photon’s. This distribution, extracted from the region of azimuthal angle opposite to the photon, acts as a proxy for the fragmentation function of the recoiling parton. Extracting it in the dense environment of a lead–lead collision required careful subtraction of the underlying event using mixed-event techniques and statistical removal of background triggers, dominated by decays of neutral pions, through a purity-based procedure.

Because the corresponding proton–proton measurement at the same photon momentum interval was statistically too limited, the collaboration used next-to-leading-order pQCD calculations without energy loss as the proton–proton reference, defining a ratio called IpQCD. These calculations have been shown to describe the published proton–proton data well, making them a sound stand-in. The result is striking: in central collisions, the ratio sits at roughly 0.5 across most of the zT range, meaning the yield of hadrons associated with the photon is cut roughly in half by the medium. In semicentral collisions the suppression is milder, and in peripheral collisions the ratio moves closer to unity, exactly the pattern expected if the quark–gluon plasma is responsible for the quenching.

The data were confronted with two state-of-the-art theoretical models that include energy loss. The first is an NLO pQCD calculation in the Higher-Twist formalism, in which the in-medium transport coefficient controls the energy loss and its parameters were extracted through a global Bayesian analysis of single-hadron, di-hadron, and photon–hadron data at several collision energies. The second is the CoLBT-hydro model, which couples the transport of jet shower partons to a (3+1)-dimensional hydrodynamic description of the expanding medium, allowing the jets themselves to excite the plasma. Both models agree with the measured D(zT) distributions and with the suppression ratios across all three centrality classes, although the current uncertainties do not yet allow the two descriptions to be distinguished from each other.

Crucially, the measurement rules out an alternative explanation. An NLO pQCD calculation that includes only cold nuclear matter effects, using nuclear parton distribution functions but no energy loss, predicts a ratio close to unity and fails to reproduce the magnitude of the suppression seen in central collisions. The suppression therefore cannot be attributed to initial-state effects alone; it demands genuine in-medium energy loss. The collaboration also computed a centrality ratio comparing central and semicentral yields to peripheral ones, finding flat distributions averaging around 0.5 and 0.75 respectively, again in agreement with the energy-loss model and confirming the expected centrality dependence of the quenching.

The measurement gains additional power from comparison with other experiments. The IpQCD results for central collisions are qualitatively compatible with CMS measurements of photon-tagged jets and of hadrons correlated with Z bosons in lead–lead collisions at the LHC, with the Z-boson comparison showing particularly good agreement given its similar centrality range and trigger momentum. They also align with direct photon–hadron correlation results from the STAR Collaboration at RHIC, which used a lower photon momentum range in more central gold–gold collisions. The PHENIX result, however, shows a significantly enhanced soft-hadron yield at low zT, likely because its lower trigger momentum means the recoiling partons lose a larger fraction of their energy, and its lower hadron threshold makes it more sensitive to soft enhancement.

By pushing the photon trigger down to 18 GeV/c, ALICE has opened a window onto a kinematic region where the largest nuclear effects are expected, probing lower momentum transfers than other LHC measurements and overlapping the momentum range explored at RHIC. This measurement serves as a benchmark for the collaboration’s Run 3 and Run 4 analyses, where vastly larger data samples will enable more precise correlations, finer centrality differentials, access to lower and higher photon momenta, and studies of how quenching depends on the orientation of the collision geometry. As the LHC continues to recreate and interrogate the hottest matter ever made in a laboratory, photons are proving to be the perfect witnesses: untouched by the inferno they illuminate, yet carrying the full story of what their partners endured on the way out.

Subject of Research: Jet quenching probed via isolated-prompt photon–hadron correlations in Pb–Pb collisions at the LHC

Article Title: Measurement of isolated-prompt photon–hadron correlations in Pb–Pb collisions at (\sqrt{{s}_{{\textrm{NN}}}} = 5.02) TeV

Article References: ALICE Collaboration, Abdallah, D. A. H., Abualrob, I. J., Acharya, S., Agarwal, K., Rinella, G. A., Aglietta, L., Agrawal, N., Ahammed, Z., Ahmad, S., Ahuja, I., Akbar, Z., Akishina, V., Al-Turany, M., Alessandro, B., Alfarasyi, A. R., Molina, R. A., Ali, B., Alici, A., … Zurlo, N. (2026). Measurement of isolated-prompt photon–hadron correlations in Pb–Pb collisions at $$\sqrt{{s}_{{\textrm{NN}}}} = 5.02$$ TeV. The European Physical Journal C, 86(9), Article 1126. https://doi.org/10.1140/epjc/s10052-026-16192-z

Image Credits: AI Generated

DOI: 10.1140/epjc/s10052-026-16192-z

Keywords: ALICE, LHC, quark–gluon plasma, jet quenching, photon–hadron correlations, Pb–Pb collisions, heavy-ion physics, fragmentation function, energy loss, pQCD, RHIC, CMS