Stability

A team at Yunnan University, led by Hongjun Wu and colleagues, with contributing researchers from Kunming University of Science and Technology, has reported a 20.96% efficient CsPbI_3-xBr_x inorganic perovskite solar cell (IPSC), achieved through a new surface passivation molecule built around a sulfonamide group. The result is described as the highest efficiency reported to date for SnO₂-based IPSCs, and the unencapsulated devices also showed strong long-term stability.

All-inorganic CsPbI_3-xBr_x perovskites are of interest for PV applications because of their thermal stability and suitability for tandem architectures, but their surfaces are prone to undercoordinated Pb²⁺ defects. These form when iodide ions migrate out of the lattice under heat, moisture or illumination, leaving behind halogen vacancies that act as non-radiative recombination centers and degrade both efficiency and long-term performance. To address this, the researchers introduced 4-aminomethylbenzenesulfonamide (4-AMBSA), a π-conjugated molecule carrying both an amino (-NH₂) and a sulfonyl (-SO₂-) group, onto the CsPbI_3-xBr_x surface.

Researchers at the University of Colorado Boulder's Renewable and Sustainable Energy Institute, led by Alex Zunger, working with the University of Sao Paulo, have shown that two simple structural measurements can predict how stable a halide perovskite alloy will be and what band gap it will have, without running a full quantum simulation for every composition.

Alloying is central to tuning perovskite light absorption and stability, but predicting which combinations of halogens, alkali metals and other elements will work has typically required slow, computationally expensive density-functional theory (DFT) calculations run one composition at a time. The team instead looked for structural descriptors that could stand in for those calculations. Running systematic DFT calculations across alloy families with substitutions at the halogen (X-site), alkali (A-site) and group-IV (B-site) positions, they found that the excess in cation-anion-cation (B-X-B') bond angles - a measure of how much the perovskite's octahedra are distorted - closely tracks the alloy's mixing enthalpy, an indicator of thermodynamic stability. Separately, the average cation-anion (B-X) bond length emerged as a reliable predictor of how the band gap shifts across the alloy series.

Researchers from Guangdong University of Technology have developed a zinc-ion (Zn²⁺) modification strategy that improves both the efficiency and the stability of all-inorganic CsPbBr₃ perovskite solar cells.

All-inorganic CsPbBr₃ perovskites are known for their excellent environmental stability compared with hybrid organic-inorganic perovskites, since they avoid the organic cations (such as MA⁺ and FA⁺) that are prone to degrading under heat, moisture, oxygen and light. That stability comes at a cost, however: CsPbBr₃'s wide bandgap (about 2.3 eV) limits light harvesting, and its films typically suffer from low crystallinity and high defect density, which drive charge recombination and hold back power conversion efficiency (PCE).

Researchers connected to Chinese flexible-perovskite maker SunFlex have published two separate papers within the same month, addressing two of the field's persistent stability problems: halide segregation in wide-bandgap perovskite/organic tandems, and desorption of the self-assembled monolayers (SAMs) used at the perovskite/electrode interface.

The first paper, from researchers at the Chinese Academy of Sciences and Shanghai Jiao Tong University - including SunFlex co-founder and CAS academician Yongfang Li - tackles a known weakness of wide-bandgap, high-bromide mixed-halide perovskites, which are used as the front cell in perovskite/organic tandem solar cells: they tend to mix unevenly during crystallization and undergo light-induced halide segregation during operation, both of which limit device performance. The team introduced a photo-transformable additive, 4-[3-(trifluoromethyl)-3H-diazirin-3-yl]benzylamine (TDB), into the perovskite precursor solution to address both problems in sequence. During crystallization, TDB suppresses the rapid precipitation of the bromide-rich phase and speeds up halide mixing during annealing, improving initial homogeneity. Then, once the device is under illumination, TDB itself transforms into a new chemical species that adsorbs more strongly onto the perovskite's grain-boundary surfaces, blocking the formation of iodide-related defects and suppressing both defect-assisted carrier trapping and ion migration - the mechanisms behind light-induced halide segregation.

Researchers from Tianjin University, Tianjin Institute of Power Sources, Beijing Institute of Technology, the Shanghai Institute of Micro-System and Information Technology (Chinese Academy of Sciences), the Ningbo Institute of Materials Technology and Engineering (Chinese Academy of Sciences), and Harbin Institute of Technology have developed a perovskite/silicon tandem solar cell for space applications that reached a certified 27.49% power conversion efficiency (PCE) under AM0 (zero air mass) illumination - which the team describes as the highest certified AM0 efficiency reported to date for this type of tandem - while also demonstrating strong resistance to electron and proton radiation and stable output during a real high-altitude balloon flight to nearly 30 km.

Perovskite/silicon tandems are attractive for space power because they combine perovskite's radiation tolerance with silicon's mature manufacturing and near-infrared response, but most previous work has focused on efficiency under standard terrestrial (AM1.5G) conditions rather than the radiation resilience and extreme thermal cycling that low Earth orbit (LEO) actually demands. In LEO, devices cycle between roughly +90°C and -90°C more than 15 times a day and face continuous bombardment by high-energy electrons and protons, which damage semiconductors through ionization and atomic displacement. In a monolithic, series-connected tandem, damage to either subcell drags down the whole device - and the researchers found that the silicon bottom cell is usually the weak link.

Researchers from Nanjing University, JA Solar, Chongqing University, Jiangsu New Energy Development Co. and Jiangsu Guoxin Research Institute have designed a new self-assembled monolayer (SAM) additive molecule that fixes a longstanding defect problem at the buried hole-transport interface of inverted perovskite solar cells, enabling a wide-bandgap perovskite cell with a champion power conversion efficiency (PCE) of 23.7% and a perovskite/silicon tandem device that reaches 33.3% (certified at 33.1%), with no measurable PCE loss after 30 days of outdoor operation.

Device configuration illustration and chemical structures of Me and TTA. Image from: Science Advances

In inverted perovskite solar cells, the SAM sitting beneath the perovskite layer governs how well the perovskite crystallizes and how efficiently charge is extracted at that buried interface. The carbazole-based SAM molecule Me-4PACz is widely used for its strong hole-extraction properties, but it tends to self-aggregate when processed from alcoholic solvents, producing uneven coverage with island-like clusters and pinholes. That patchy coverage weakens binding to both the substrate below and the perovskite above, raises interface defect density, and impairs charge transport - a problem that has proven difficult to solve without sacrificing some other aspect of performance.

Researchers from Taiwan's National Yang Ming Chiao Tung University and Flexwave have developed a self-adaptive interfacial nanostructure (SAIN) for the hole-extraction contacts of inverted perovskite solar cells, reporting a power conversion efficiency (PCE) approaching 20% under standard 1-sun illumination and 38.16% under indoor lighting at 2,000 lux - a figure that climbs above 40% once paired with an optical enhancement film, placing the device among the most efficient indoor perovskite solar cells reported to date.

The team explains that "regular" n-i-p configurations tend to reach higher efficiencies, but inverted PeSCs offer better long-term stability and are easier to stack into multijunction devices, making the p-i-n architecture an attractive target for further improvement. A major bottleneck in inverted PeSCs is the buried hole-transport layer (HTL) sitting beneath the perovskite film. Because the perovskite crystallizes directly on top of it, the HTL's quality shapes both the interface and the growing perovskite layer itself, and a poor HTL drives up non-radiative recombination - carriers lost to defects rather than converted into current, which shows up as low photoluminescence quantum yield in the finished film. Today's leading inverted devices typically grow their perovskite on either a hole-conducting polymer such as poly(triarylamine) (PTAA) or a self-assembled monolayer (SAM) built from carbazole-based molecules. Each has drawbacks: high-quality PTAA is costly to produce, while SAMs are difficult to deposit as a conformal, densely packed layer, which hurts device-to-device reproducibility. Both materials are also hydrophobic, complicating full-coverage perovskite deposition over large areas. Hybrid PTAA-plus-SAM contacts have been explored to combine their strengths, but so far only for standard 1-sun operation, leaving their potential for indoor photovoltaics untested.

Researchers from Nanjing Tech University have developed a vacuum-deposition strategy that improves the performance of fully evaporated perovskite solar cells (PSCs) by precisely controlling the solid-state reaction pathway during film formation.

Vacuum deposition is widely viewed as a scalable and solvent-free alternative to solution processing, with potential advantages for industrial integration. However, devices fabricated using this approach have historically lagged behind their solution-processed counterparts due to defects formed during crystallization. The Nanjing Tech team addressed this limitation by introducing formamidinium acetate as a reactive precursor that fundamentally alters how the perovskite phase forms.

Researchers from China's Northwestern Polytechnical University and Shaanxi Joint Laboratory of Graphene (NPU) and Southern University of Science and Technology have developed a new interfacial strategy that addresses a stubborn weak point in inverted perovskite solar cells (PSCs): the instability of the fullerene (C60) electron transport layer.

C60 and its derivatives are popular choices for electron transport layers in inverted PSCs thanks to their high electron mobility and favorable energy-level alignment with the perovskite, but suffer from intrinsic drawbacks. Its electronic disorder promotes trap-assisted recombination, which narrows the quasi-Fermi level splitting and drags down the open-circuit voltage. Just as importantly, C60's high molecular symmetry and weak intermolecular bonding make it prone to thermodynamically driven aggregation as the film forms - which worsens under light and heat. As the fullerene agglomerates, contact across the perovskite/C60 interface deteriorates, interface resistance climbs, charge transport suffers, and the device degrades faster. Functionalized C60 derivatives can improve compatibility and morphology, but the added groups often leave the material even more vulnerable to stress-induced breakdown. To break this cycle, the team designed an acceptor-donor-type metallopolymer, "polycarbolong," and used it to build what they call a corrugated polycarbolong interlocking (CPI) layer at the interface. 

A research team, led by Prof. Michael McGehee at the University of Colorado Boulder, working with groups at Northwestern University, the University of Arizona, the University of Washington and the National Laboratory of the Rockies (NLR, the new name for the National Renewable Energy Laboratory), has identified the mechanism behind the slow degradation of perovskite solar cells under reverse bias — and demonstrated a fix that requires no new materials or equipment.

Reverse bias is the electrical condition that arises when part of a panel is shaded while the rest sits in full sunlight. It has long been known to damage perovskite devices, but the picture was incomplete. Current can flow under reverse bias by two routes. Where films contain large defects, electrons rush through those sites and destroy the cell outright - an acute failure mode the same group addressed in an earlier study. The second route persists even in films without such defects: current leaks through by quantum tunnelling, distributed across the whole device, degrading it gradually rather than abruptly. That slower pathway has been far harder to characterize, and existing theories could not explain why some cells degraded so quickly, or why certain architectures proved much more resilient than others.