Writing in Nature Materials, the team describes how a single chemical modification—a chlorine atom placed at the para position of a phenethylammonium cation—transforms the stability of two-dimensional tin iodide perovskites. The resulting material, based on the 4-chloro-phenethylammonium (4ClPEA) cation, forms ultrastable two-dimensional and quasi-2D tin halide perovskites that retain bright photoluminescence for several months when simply left out in ambient air. When incorporated into 2D/3D perovskite solar cells, the chlorinated cation delivers devices with a power conversion efficiency of 16.2 percent, alongside operational stability exceeding 1,000 hours at 55 degrees Celsius in air—a combination of efficiency and durability that few tin-based devices have ever approached.

The key insight behind the work lies in how the organic spacer cations that separate the inorganic tin iodide sheets influence what happens between those sheets. In the layered Ruddlesden–Popper architecture of two-dimensional perovskites, bulky organic cations cap the corners of the octahedral framework and stack on top of one another between the inorganic slabs. The researchers systematically compared a family of halogen-substituted phenethylammonium cations—4XPEA, where X is hydrogen, fluorine, chlorine, or bromine—in the model compound (4XPEA)2SnI4. Single-crystal X-ray diffraction revealed that the chlorinated variant packs the organic layers more tightly than any of its siblings, driven by stronger π-stacking interactions between the aromatic rings.

That tighter packing is not merely a crystallographic curiosity. Using computational modeling and diffusion analysis, the team showed that the densely interlocked organic layers in (4ClPEA)2SnI4 substantially impede the diffusion of oxygen and water molecules into the vulnerable inorganic sheets. In effect, the chlorinated aromatic rings act as a molecular raincoat, sealing the gaps through which air would otherwise infiltrate and oxidize the tin(II) centers. The fluorinated and brominated analogues, by contrast, leave the interlayer region more permeable, and their films degrade noticeably faster under identical conditions. The result establishes a direct structure–property relationship: the tighter the interlayer packing, the greater the resistance to oxidative degradation.

Stability alone, however, would be of limited value if the material could not be turned into a high-quality solar absorber. The second half of the study addresses the notoriously uncontrolled crystallization of tin halide perovskites. Tin-based films tend to crystallize too quickly and too chaotically during deposition, producing pinholes, poor orientation, and defective grain boundaries that accelerate degradation and squander charge carriers. Here again, the 4ClPEA cation proved decisive. When added to three-dimensional tin iodide perovskite precursor solutions, it steers film growth toward markedly improved crystallinity and preferred crystallographic orientation, yielding dense, well-ordered 2D/3D heterostructured films.

Grazing-incidence wide-angle X-ray scattering measurements confirmed the enhanced orientation and phase purity of the treated films, while time-of-flight secondary ion mass spectrometry mapped the distribution of the organic cation through the film thickness. Density functional theory calculations provided a mechanistic underpinning, indicating favorable interactions between the chlorinated aromatic ring and the iodide species at the perovskite surface—an anion–π interaction that helps template orderly growth. The combination of a well-oriented 3D absorber with a protective 2D capping layer is precisely the architecture that the field has been pursuing for lead-based perovskites, and the study demonstrates that it can be realized in the tin system with the right molecular tool.

The device results are striking in context. Lead-free tin perovskite solar cells have historically lagged far behind their lead-containing counterparts, with certified efficiencies only recently crossing the 14 percent threshold and most devices failing within hours or days of operation. The 16.2 percent efficiency achieved with the 4ClPEA-based 2D/3D films places this work among the best-performing tin perovskite photovoltaics reported to date. More importantly, the devices did not merely perform well on the bench immediately after fabrication; they endured more than 1,000 hours of continuous operation at an elevated temperature of 55 degrees Celsius in ambient air, conditions that combine thermal stress, oxygen exposure, and moisture—the three horsemen of perovskite apocalypse.

The broader significance of the work extends beyond a single efficiency number. Tin halide perovskites are considered essential building blocks for the next generation of all-perovskite tandem solar cells, where a narrow-bandgap tin or tin–lead bottom cell would be paired with a wide-bandgap lead top cell to push efficiencies beyond what silicon can deliver. Lead toxicity, however, remains a persistent regulatory and public-acceptance obstacle, and studies quantifying the biological impact of lead leakage from perovskite modules have underscored the risk of assuming any safe threshold. A durable, efficient, entirely lead-free absorber would remove that obstacle while simplifying encapsulation requirements, and the chlorinated-cation strategy offers a generalizable design principle: choose spacer cations whose substituents promote tight interlayer packing and strong surface interactions.

The researchers also emphasize that the approach is rooted in fundamental chemistry rather than device engineering tricks. By comparing the full series of halogenated phenethylammonium cations, they isolated the effect of the substituent on π-stacking, interlayer spacing, and barrier properties, showing that chlorine occupies a sweet spot among hydrogen, fluorine, and bromine. The team has filed a patent application on the technology, and the design motif—electron-withdrawing substituents on aromatic spacer cations to tighten packing and passivate surfaces—could plausibly be extended to germanium-based perovskites, low-dimensional emitters, and other tin-containing optoelectronic devices where air sensitivity has been the limiting factor.

Challenges remain before tin perovskite solar cells can compete commercially. The efficiency gap with lead-based devices, which now exceed 27 percent, is still substantial, and scaling the chemistry from laboratory cells to modules will require further optimization of deposition and encapsulation. But the demonstration that a single atom of chlorine, placed with chemical intent on an organic cation, can buy months of ambient stability and a thousand hours of hot operation represents a genuine inflection point. For a field that has watched its most promising lead-free materials crumble within days, the message is clear: the path to practical tin photovoltaics may run through the careful engineering of the molecules that sit between the crystals, not just the crystals themselves.

Subject of Research: Stable 2D/3D tin halide perovskite solar cells enabled by a chlorinated organic spacer cation

Article Title: A chlorinated organic cation enables stable 2D/3D tin iodide perovskite photovoltaics

Article References: Triggs, C. T., Chen, L., Xie, J., Weadock, N. J., Zhang, Z., Ye, J. Y., Kerner, R. A., Taddei, M., Yang, F., Addison, B., Wang, X., Liu, T., Harvey, S. P., Toney, M. F., Beard, M. C., Yan, Y., Zhu, K., & Jin, S. (2026). A chlorinated organic cation enables stable 2D/3D tin iodide perovskite photovoltaics. Nature Materials. https://doi.org/10.1038/s41563-026-02726-z

Image Credits: AI Generated

DOI: 10.1038/s41563-026-02726-z

Keywords: tin halide perovskite, perovskite solar cells, lead-free photovoltaics, 4-chloro-phenethylammonium, 2D/3D heterostructure, air stability, π-stacking, crystallization control, power conversion efficiency, Ruddlesden–Popper perovskite, tin oxidation, Nature Materials

The problem with copper is fundamental to the physics of charge transport at small scales. In a bulk metal, electrons travel long distances before scattering off imperfections, giving copper its famously low resistivity of about 1.7 micro-ohm centimetres. But when a wire’s dimensions approach the mean free path of its electrons, two effects conspire to raise resistance dramatically. Electrons begin to scatter off the surfaces and grain boundaries of the wire, and the effective cross-section available for conduction shrinks. In state-of-the-art copper interconnects, which in the most advanced chips have critical dimensions below 20 nanometres, this size effect causes resistivity to soar, producing signal delays, wasted power and degraded reliability. As the semiconductor industry pushes toward ever-denser circuitry, the wires that tie transistors together have become a limiting factor in computing performance.

The Hong Kong Polytechnic University team, together with collaborators at South China Normal University, The Hong Kong University of Science and Technology, The University of Hong Kong, the Taiwan Semiconductor Research Institute and National Taiwan Normal University, turned to an unconventional class of conductors: topological semimetals. Materials such as CoSi host exotic electronic states in which electrons are protected from backscattering by the topology of their band structure. In particular, CoSi possesses long-lived Fermi-arc surface states, chiral electronic pathways that live on the surfaces of the crystal and are remarkably resistant to the scattering that plagues ordinary metals. The researchers reasoned that if these surface states are highly conductive, then making the material thinner, which increases the surface-to-volume ratio, should improve rather than degrade its overall conductivity.

To test this idea, the team grew high-quality single crystals of CoSi and fabricated nanoflakes with thicknesses spanning from one micrometre down to roughly 20 nanometres. The results were unambiguous and, by the standards of conventional metals, almost paradoxical. As the CoSi thickness decreased from 1 micrometre to about 20 nanometres, the resistivity dropped from 7.0 to 0.72 micro-ohm centimetres, a nearly tenfold improvement. The highly conductive surface path, dominated by the topological Fermi-arc states, progressively takes over as the bulk contribution diminishes with thickness. At room temperature, the resistivity of 20-nanometre-thick CoSi is one-tenth that of copper at the same thickness, a margin that could transform the design of the wiring layers in future chips.

Conductivity alone, however, is not enough to qualify a material as an interconnect candidate. Chip wiring must survive brutal operating conditions. Current densities in modern interconnects can exceed millions of amperes per square centimetre, and the resulting momentum transfer from electrons to metal atoms drives electromigration, the gradual transport of atoms that eventually opens voids and breaks the wire. Copper is particularly vulnerable at small dimensions, where grain boundaries and surfaces provide fast diffusion pathways for atoms. The CoSi semimetal, by contrast, is held together by exceptionally strong bonding. The researchers calculated a cohesive energy of 5.4 electronvolts and an atom migration barrier of 3.7 electronvolts, values far higher than those of copper. Experimentally, CoSi nanoflakes maintained reliable conduction at current densities of up to 10^8 amperes per square centimetre and at temperatures up to 450 degrees Celsius, performance that positions the material among the most robust thin-film conductors ever characterized.

The team also verified that CoSi can handle the high-frequency demands of modern communications circuitry. Radiofrequency measurements showed that CoSi interconnects operate cleanly at frequencies up to 40 gigahertz, a regime relevant to wireless transceivers, high-speed data links and advanced processors. Low loss and stable impedance at these frequencies are essential for any material hoping to replace copper in the back-end-of-line metallization of a chip, and the measurements suggest that CoSi’s smooth single-crystalline surfaces and low resistivity translate directly into excellent high-frequency behaviour.

Perhaps most convincingly, the researchers moved beyond isolated test structures and integrated a CoSi interconnect into a functioning silicon circuit. They connected a 16-nanometre-node silicon ring oscillator, a standard benchmark circuit used to evaluate process technology, using CoSi wiring. The oscillator operated at the same frequency as an identical circuit wired with conventional metal interconnects, demonstrating that the exotic semimetal can be married to mainstream silicon manufacturing without degrading circuit performance. This on-chip demonstration is a critical milestone, because many promising nanomaterials have faltered at exactly this step, proving difficult to integrate with the complementary metal-oxide-semiconductor processes that underpin the global electronics industry.

The findings arrive at a moment of intense searching within the semiconductor community. As copper interconnects approach their physical limits, researchers have explored a wide range of alternatives, including graphene, carbon nanotubes and other topological semimetals such as NbAs, NbP and MoP. Recent studies have shown surface-dominated transport in Weyl semimetal nanowires and ultrahigh conductivity in NbAs nanobelts, but questions of manufacturability, reliability and integration have kept any successor to copper out of production. CoSi stands out because it combines several advantages at once: a resistivity that improves with scaling, extraordinary electromigration resistance, thermal stability well beyond typical chip operating temperatures, proven high-frequency performance and demonstrated compatibility with a commercial silicon technology node.

There are, of course, hurdles between a laboratory demonstration and a production line. The CoSi nanoflakes in this study were grown and characterized as single crystals, and future work will need to establish scalable deposition methods, patterning techniques and via integration compatible with high-volume manufacturing. The contact resistance between CoSi and other chip materials, the chemical stability of the semimetal during processing, and the cost of adopting a new metallization scheme all remain open engineering questions. Still, the fundamental physics reported here inverts the central dilemma of interconnect scaling. Instead of fighting a material that gets worse as it gets smaller, chip designers could embrace one that gets better, turning the relentless miniaturization that once threatened copper wiring into an advantage for topological semimetals.

If CoSi and its relatives can clear the remaining manufacturing barriers, the implications extend beyond faster smartphones and data centres. Interconnect resistance is a growing share of the energy budget of modern computing, and taming it would reduce power consumption across everything from cloud servers to edge devices. The work also signals a broader convergence between topological quantum materials and mainstream electronics, a field long dominated by theoretical promise rather than practical devices. With a material that conducts better at 20 nanometres than at a micrometre, survives currents that vaporize copper and runs at 40 gigahertz inside a working silicon chip, the researchers have offered the semiconductor industry a glimpse of what may come after copper, and a reason to believe that the end of transistor scaling is not, after all, the end of computing progress.

Subject of Research: Single-crystalline cobalt silicide (CoSi) semimetal as a highly conductive and reliable nanoscale interconnect material to replace copper in advanced chips

Article Title: Single-crystalline CoSi semimetals with high conductivity and reliability

Article References: Chen, J., Yan, J., Fan, L., Zheng, T., Che, X., Zhu, C., Lu, W., Deng, M., Ng, Y. H., Wang, Z., Wan, Y., Jiang, X., Zhu, Y., Yang, Z., Chen, K. J., Liang, B.-W., Li, K.-S., Lan, Y.-W., Li, L.-J., & Chai, Y. (2026). Single-crystalline CoSi semimetals with high conductivity and reliability. Nature Materials. https://doi.org/10.1038/s41563-026-02740-1

Image Credits: AI Generated

DOI: 10.1038/s41563-026-02740-1

Keywords: CoSi, semimetal, interconnects, copper replacement, topological materials, resistivity scaling, electromigration, nanoelectronics, Fermi arcs, ring oscillator, Nature Materials, chip wiring

Moiré patterns arise whenever two periodic lattices are overlaid with a slight rotational misalignment, producing a long-wavelength interference superlattice that can profoundly alter electronic behavior. The phenomenon became world-famous with magic-angle twisted bilayer graphene, where twisting two graphene sheets by about 1.1 degrees unleashed unconventional superconductivity. Until now, however, moiré engineering has been pursued almost exclusively as a route to emergent quantum states in atomically thin heterostructures, typically assembled layer by layer under demanding laboratory conditions. The new work demonstrates that the same rotational degree of freedom, when distributed throughout the interior of a bulk crystal, can serve an entirely different purpose: dissipating mechanical stress and preventing catastrophic fracture.

The research team, led by scientists at the Shanghai Institute of Ceramics of the Chinese Academy Sciences together with collaborators at Zhejiang University, concentrated on gallium germanium telluride, GaGeTe, a ternary layered van der Waals semiconductor. Like other van der Waals crystals, GaGeTe consists of robust covalently bonded sheets held together by weak interlayer forces, which allows individual layers to slip relative to one another. In a pristine, perfectly aligned crystal, the layers share a common crystallographic orientation, and under tension the material tends to fail through the initiation and rapid propagation of cracks. The researchers reasoned that if adjacent layers were rotated with respect to each other, the mismatch between their lattices would create moiré superlattices that fundamentally change how stress is accommodated during deformation.

Introducing such twists into a bulk crystal might seem to require assembling it layer by layer, but the team found a remarkably simple route. By applying compression along an axis slightly off the crystal’s principal orientation, they controllably generated interlayer moiré twisting spanning a broad range of angles commensurate with the crystal’s translational symmetry. The magnitude of the twist could be tuned through the degree of pre-compression: samples compressed by 5, 10, and 20 percent developed distinct distributions of twist angles, as revealed by transmission electron microscopy and synchrotron-based diffraction techniques. Three-dimensional precession electron diffraction tomography and Rietveld refinement of synchrotron powder diffraction data confirmed the structural integrity and composition of the treated crystals, while in situ TEM tensile experiments captured the moiré patterns evolving in real time as the material was stretched.

The mechanical consequences were striking. When the pre-compressed, twisted crystals were subsequently pulled in tension at room temperature, their stress–strain curves revealed a transformation from brittle to genuinely ductile behavior. Where untreated GaGeTe fractured after limited elastic and plastic elongation, the twisted crystals sustained tensile strains approaching 30 percent, an increase of up to 360 percent in macroscopic ductility. Critically, the enhancement scaled with the twist angles introduced by compression: higher pre-compression levels produced larger interlayer rotations and correspondingly greater stretchability. The team also verified that the effect persisted across variations in sample thickness and strain rate, underscoring that the mechanism is intrinsic to the twisted architecture rather than an artifact of a particular testing configuration.

The origin of this extraordinary plasticity lies in how moiré superlattices facilitate stress relaxation. Under mechanical loading, the twist angles between neighboring layers continue to increase, allowing the crystal to accommodate deformation through widespread interlayer slipping rather than through the nucleation of fatal cracks. In an untwisted crystal, slipping is constrained by the periodic registry between layers, and once a micro-crack forms, the covalent bonds within a layer offer little resistance to its propagation. In the twisted configuration, the moiré modulation effectively homogenizes and redistributes the interlayer potential energy landscape, lowering the barriers to slip along the basal planes. Density functional theory calculations of generalized stacking fault energies and crystal orbital Hamilton populations supported this picture, showing reduced slip energies and modified Te–Te and Te–Ga bonding along slipping pathways in twisted structures.

Direct atomic-scale imaging told a complementary story. High-angle annular dark-field scanning transmission electron microscopy of deformed samples revealed intralayer bending, ripplocations, and micro-cracks that remained arrested rather than propagating through the entire crystal. In situ TEM tensile videos documented moiré patterns with small twist angles of roughly 1.5 degrees at early deformation stages, growing to approximately 6 degrees as tensile strain accumulated, with the progressive twisting acting as a built-in reservoir for plastic accommodation. The researchers also constructed idealized twist-stacked models, denoted θ-GaGeTe, with alternating layers rotated by specific angles ranging from about 1.5 to nearly 22 degrees; simulated moiré patterns for these structures matched the experimentally observed contrast, validating the structural interpretation of the deformation mechanism.

Perhaps the most important practical feature of the approach is its selectivity. Because moiré twisting occurs only between layers while the atomic arrangement within each layer remains intact, the in-plane electronic properties that make these materials attractive for devices are essentially untouched. This stands in contrast to many toughening strategies that rely on defects, grain boundaries, or alloying, all of which can severely degrade charge transport, optical response, or thermoelectric performance. The authors also demonstrated the generality of the concept beyond GaGeTe: off-axis compression produced comparable enhancements in tensile plasticity across a family of bulk van der Waals crystals including GaS, GaSe, InSe, CrSiTe3, InSiTe3, and SnBi2Te4, suggesting the strategy is broadly applicable to the entire class of layered semiconductors.

The implications reach into several technology areas where mechanical fragility has long limited deployment. Flexible thermoelectrics, which convert waste heat into electricity in conformable formats, depend on semiconductors that can bend and stretch without failing; earlier work by some of the same groups established ductile inorganic semiconductors and exceptional plasticity in materials such as InSe and Bi2Te3-based crystals. The moiré-twisting strategy adds a new, geometrically driven lever to that toolkit, one that is compatible with the demanding electronic requirements of thermoelectric and optoelectronic devices. It may likewise inform the design of two-dimensional-material-based transistors, photodetectors, and silicon photonics components, where GaGeTe itself has recently been integrated into electro-optic devices, by improving the mechanical robustness of bulk crystals used as feedstock or substrates.

From a fundamental standpoint, the study expands the conceptual scope of moiré physics from quantum emergent phenomena to classical mechanics of deformation. It shows that a structural parameter long treated as an electronic tuning knob can double as a mechanical design variable, decoupled from in-plane transport. The work was supported by the National Natural Science Foundation of China, the Chinese Academy of Sciences, and Shanghai municipal programs, with synchrotron experiments performed at the RIKEN BL44B2 beamline of SPring-8 in Japan. As research groups worldwide continue to explore twistronics for superconductivity, magnetism, and correlated electron physics, this result suggests a parallel track: twisting crystals to make them tough. If the strategy can be scaled from laboratory single crystals to manufactured components, the humble rotational misalignment between atomic layers may become one of the most versatile tools in the materials engineer’s repertoire, turning inherently brittle semiconductors into materials that bend, stretch, and survive the demands of real-world flexible technology.

The result also reframes a long-standing dichotomy in materials science. Metals derive their ductility from dislocations, dense arrays of line defects that glide through the crystal lattice and dissipate strain; conventional semiconductors, with their stiff covalent bonding and scarcity of mobile defects, have almost always been relegated to the brittle side of that divide. The moiré-twisting mechanism offers a third route: rather than relying on point or line defects introduced during growth or processing, it exploits a rotational degree of freedom that is deliberately programmed into the stacking sequence itself, effectively designing the deformation pathway in advance.

The approach resonates with recent independent demonstrations that twist can strengthen otherwise fragile solids. Twisted-layer boron nitride ceramics have shown high deformability and strength, and twist-assisted toughening has been reported in two-dimensional transition metal dichalcogenides, indicating that rotational misalignment is emerging as a general design principle spanning scales from atomically thin films to bulk ceramics. The present study extends this principle to ternary van der Waals semiconductors and, crucially, shows that the twist can be introduced after synthesis by a scalable mechanical step rather than during crystal growth.

For practical adoption, the compatibility with existing characterization and processing workflows matters. Off-axis compression requires no epitaxial assembly, no layer-by-layer transfer, and no exotic chemistry, which means the treatment could in principle be applied to crystals grown by conventional bulk methods. Because the twist angles are commensurate with the crystal’s translational symmetry, the resulting superlattices are periodic and well defined, making the deformed crystals amenable to standard diffraction-based quality control before device fabrication.

Open questions remain, including how the twist distributions evolve under cyclic loading, elevated temperature, and long-term operation, and whether the ductility gains persist when crystals are integrated into multilayer device stacks. Answering these will determine whether moiré-twisted semiconductors move from laboratory demonstrations into flexible thermoelectric modules, wearable sensors, and compliant photonic platforms.

Subject of Research: Enhancing tensile plasticity of bulk van der Waals crystals through tunable interlayer moiré twist angles

Article Title: Tuning moiré twist angles enhances tensile plasticity in bulk van der Waals crystals

Article References: Zhou, J., Zou, J., Gao, Z., Zhang, J., Zhang, L., Li, Z., Zhou, Z., Qiu, P., Yang, Y., Yu, Q., Chen, L., & Shi, X. (2026). Tuning moiré twist angles enhances tensile plasticity in bulk van der Waals crystals. Nature Materials. https://doi.org/10.1038/s41563-026-02731-2

Image Credits: AI Generated

DOI: 10.1038/s41563-026-02731-2

Keywords: moiré twisting, van der Waals crystals, tensile ductility, GaGeTe, off-axis compression, plastic deformation, two-dimensional materials, twistronics, semiconductors, flexible electronics, interlayer slipping, Nature Materials