Researchers reported on September 1, 2026 a flexible perovskite solar cell that delivers a champion power conversion efficiency (PCE) of 25.21% — among the highest ever recorded for a single-junction device on a bendable substrate — while retaining more than 85% of that output after 10,000 bending cycles. The achievement, published as a Version of Record in Advanced Functional Materials (Wiley), rests on a single processing step borrowed from the kitchen rather than the chemistry laboratory: a post-treatment built around the potassium salt of theanine, the amino acid responsible for the umami flavor of green tea. That the same molecule that makes high-grade matcha taste the way it does can simultaneously suppress electron-hole recombination losses and toughen a solar film against mechanical fatigue is the finding’s most counterintuitive — and commercially consequential — feature.
Flexible perovskite solar cells (f-PSCs) have tantalized engineers for years: lightweight, bendable films that could laminate onto curved building facades, power wearable electronics, integrate into vehicle roofs, or unroll from a reel in continuous manufacturing runs. Their efficiency has climbed steadily — from below 4% in 2009 to beyond 25% in recent laboratory demonstrations — but two persistent barriers have blocked commercial readiness.
The first is interfacial non-radiative recombination. Perovskite films absorb sunlight brilliantly, generating electron-hole pairs that should flow as electrical current. But at the buried interface between the tin oxide (SnO2) electron transport layer and the perovskite absorber, crystallographic imperfections, undercoordinated metal ions, and mismatched energy levels create trap states — defect sites where charge carriers recombine and release their energy as heat before reaching an electrode. Each trap state that fires costs the device a fraction of its voltage and current. Suppressing this loss is the central efficiency challenge for the entire perovskite photovoltaic field, as detailed in non-radiative recombination losses across flexible architectures.
The second barrier is mechanical fragility. Flexible cells are built on polymer substrates — polyethylene naphthalate (PEN) or polyethylene terephthalate (PET) — that deform under normal use. Each bend stresses the perovskite film and its interfaces, propagating microcracks that degrade both charge transport and long-term output. High bending endurance without sacrificing efficiency, and without adding structural reinforcement that raises cost and weight, has proven difficult to achieve simultaneously.
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The new study addresses both problems using a nanoscale dual-modulation strategy, reported in Advanced Functional Materials (2026). Theanine — specifically its potassium salt, P-DLTh in the literature — is introduced into the SnO2 nanocrystal suspension before the electron transport layer is deposited. This “bottom-up” approach means the molecule is already embedded in the ETL when the perovskite film forms on top of it, positioning theanine at exactly the location where both problems originate.
Theanine (γ-glutamylethylamide) is a non-protein amino acid found almost exclusively in tea plants (Camellia sinensis). It accounts for more than half the free amino acids in high-quality green tea, and it is the compound responsible for tea’s distinctive umami-sweet taste. It has been commercially produced at scale since the 1990s as a food additive, a supplement ingredient, and a flavor component — and it carries theanine’s GRAS food-safe status in the United States food system.
That background matters here. Most advanced surface passivation strategies for perovskite cells rely on bespoke synthetic organic molecules — designed for the task, produced by multi-step organic synthesis, and available only from specialty chemical suppliers. Theanine is none of those things. It is a commodity amino acid with an established global supply chain. A solar cell post-treatment built around it inherits that supply chain: no new feedstocks, no exotic synthesis routes, no procurement risk at scale. The green chemistry credential is not merely nominal — it connects directly to the commercial practicality of the approach.
Chemically, the potassium theanate molecule carries an ionizable carboxylate group, an amide linkage, and a terminal amine — three distinct functional groups capable of bonding to different surfaces at the SnO2/perovskite interface. The paper describes what it calls a triple-layer passivation system: the molecule coordinates simultaneously to defects in the SnO2 bulk, to undercoordinated atoms on the SnO2 surface, and to exposed lead ions (Pb²⁺) and halide vacancies at the buried perovskite interface above. Each bonding site suppresses a different category of non-radiative recombination loss, as documented in Advanced Functional Materials (2026).
The mechanical benefit follows from the same coordinated network. The cross-linked interlayer that theanate forms across the SnO2/perovskite junction distributes mechanical stress during bending rather than concentrating it as a shear force at the interface. Where an unmodified buried interface would crack and delaminate under repeated flexion, the theanate-bonded junction accommodates strain without fracture — accounting for the more than 85% PCE retention observed at 10,000 bending cycles, as reported in Advanced Functional Materials (2026).
The efficiency number is notable. The bending durability is competitive. But the production method is what makes this result editorially distinct from most laboratory advances in the flexible perovskite field.
Nearly all high-performance flexible perovskite cells demonstrated in literature — including the prior 25.09% flexible record with 90% retention at 10,000 bending cycles — have required fabrication in inert-atmosphere environments: nitrogen- or argon-filled gloveboxes, or carefully controlled dry rooms with humidity below 10%. Those environments are capital-intensive and throughput-limiting. They are incompatible with roll-to-roll (R2R) manufacturing at anything like commercial speed and cost, because maintaining an inert atmosphere across a continuously moving web is technically and economically prohibitive.
Korea’s Institute of Materials Science (KIMS) named this constraint explicitly in work published in the Chemical Engineering Journal in 2025. The KIMS team, led by Dr. Dong-chan Lim and Dr. So-yeon Kim, developed a related KIMS ambient-air flexible work, stating that the work “demonstrates a technology for fabricating perovskite solar cells without the need for expensive temperature- and humidity-controlled environments, while also exhibiting one of the highest levels of mechanical stability among flexible solar cells developed to date.”
The new Advanced Functional Materials paper operates in the same philosophy but pushes the efficiency ceiling higher. Because theanine salt is applied from solution at room temperature, and because SnO2 is deposited from commercial aqueous dispersions compatible with ambient air, the entire critical interface-engineering step requires no glovebox. An R2R production line could in principle insert this post-treatment without specialized atmospheric controls, reducing both capital expenditure and processing cost at scale. A 2025 ambient-air R2R compatibility review identified ambient-air coating compatibility as the specific prerequisite desirable for practical R2R viability in flexible perovskite manufacturing.
At 25.21%, the new device sits at or above the frontier for single-junction flexible perovskite photovoltaics under standard AM1.5G sunlight. For context:
The January 2026 Nature Energy paper — using β-cyclodextrin derivatives to reinforce grain boundaries and assemble an amorphous interlayer — achieved 24.52% PCE with 92.5% retention after 10,000 bending cycles, and demonstrated large-area flexible modules up to 1.4725 m² (15.85 ft²) delivering 226 W of output. That result was widely cited as establishing the prior state-of-the-art in the dual efficiency-plus-durability category.
The new result pushes the efficiency figure to 25.21% — approximately 0.7 percentage points higher — while maintaining competitive bending durability. Whether the result can match the Nature Energy paper’s module-scale and outdoor stability demonstrations remains an open question; those data are not disclosed in the published abstract.
The difference in device architecture is also worth noting. The Nature Energy study built its grain boundary reinforcement into the perovskite film itself, using a self-assembly approach. The new paper’s strategy is buried-interface-first: the theanate molecule is embedded in the ETL before the perovskite forms, which could simplify integration into existing SnO2-based device stacks without modifying the perovskite precursor formulation.
For comparison, single-junction rigid perovskite cells now exceed 26.7% certified efficiency (University of Science and Technology of China, NREL-verified). Flexible formats have historically lagged rigid equivalents by 1–2 percentage points due to the additional constraints of polymer substrates and the absence of high-temperature processing. A 25.21% flexible result approaches that gap — and does so without the glovebox-based fabrication that most high-efficiency rigid demonstrations rely on.
Read more: Berlin Lab Solves Perovskite Solar’s Stability Problem With Graphene-Oxide Interface Fix
The applications that flexible perovskite photovoltaics are designed for share a common characteristic: silicon panels cannot serve them. Rigid silicon wafers are brittle, heavy, and planar. They cannot be shaped to curves, embedded in textiles, laminated to vehicle rooflines, or integrated into architectural glass — not without prohibitive structural complexity.
Flexible perovskite cells address all of those markets. Building-integrated photovoltaics (BIPV) — solar-generating facades, windows, and roofing materials — need thin, lightweight films that conform to architectural surfaces. Wearable electronics need bendable power sources that survive repeated flexion without performance loss. Vehicle-integrated photovoltaics need cells that follow the contours of hoods, roofs, and body panels. The Internet of Things needs distributed sensor nodes with their own durable power supply.
The global flexible perovskite solar cell market was valued at approximately $94.2 million in 2025, according to the flexible perovskite market report from Fortune Business Insights. The firm projected the market would reach approximately $145.4 million in 2026, expanding to $1.08 billion by 2034 at a compound annual growth rate of 28.43%. The BIPV segment leads in end-use share. Commercialization, market analysts consistently note, is conditioned on resolving exactly the stability and mechanical durability challenges this research addresses.
The 25.21% figure is a champion-cell measurement: a single device optimized under controlled laboratory conditions, measured on a small active area. It has not been independently certified by an accredited photovoltaic calibration laboratory (NREL, Fraunhofer CalLab, or equivalent). In the perovskite field, published champion efficiencies routinely exceed independently certified values by 0.5–1.5 absolute percentage points; certification is the standard the investment and commercialization community scrutinizes. The paper also does not report module-scale results — where engineering factors including current mismatch, interconnect losses, and edge effects typically reduce efficiency by several percentage points compared to small-area cells.
The more than 85% PCE retention at 10,000 bending cycles is a mechanical fatigue benchmark under laboratory conditions. It does not incorporate outdoor degradation stressors: UV exposure, humidity cycling, thermal cycling across seasonal temperature swings, or combined mechanical-plus-environmental aging. Real-world durability is the test that commercial warranties require.
Finally, the perovskite absorber itself contains lead — lead halide perovskites remain the dominant high-efficiency formulation across rigid and flexible architectures. Lead leaching from failed cells is a documented environmental and regulatory concern for consumer products; lead-free alternatives (tin-based, bismuth-based) have not yet reached equivalent efficiency levels. This constraint applies to virtually the entire competitive field, not to this study specifically, but it is a commercialization consideration that the industry has not yet resolved.
Theanine (γ-glutamylethylamide) is a non-protein amino acid found almost exclusively in tea plants (Camellia sinensis), where it accounts for more than half the plant’s free amino acids and is responsible for the umami-sweet taste of green tea. It has been commercially produced as a food additive and supplement ingredient for decades, giving it theanine’s GRAS food-safe status in the US food system. In this study, its potassium salt form is used as a solar cell passivation agent because its multiple functional groups — a carboxylate, an amide, and an amine — can simultaneously coordinate to defect sites on both the tin oxide electron transport layer and the perovskite absorber surface above it. Unlike bespoke synthetic passivation molecules that must be specially manufactured, theanine is a commodity chemical with an established global supply chain — which is part of why the researchers describe this as a “green” post-treatment.
It is among the highest figures recorded for a single-junction flexible perovskite device under standard AM1.5G sunlight as of September 2026, but the field is moving rapidly and the specific record depends on how device categories are defined. The January 2026 Nature Energy paper using β-cyclodextrin grain-boundary reinforcement achieved 24.52%, and some reviews cite earlier results approaching 25.44% for the broader flexible format. The 25.21% figure in this paper has not yet been independently certified by an accredited laboratory such as NREL or Fraunhofer CalLab, which is the standard the solar community uses to compare results across groups. Champion-cell measurements and certified efficiency figures can differ by up to 1.5 percentage points.
Most high-performance perovskite solar cells — rigid or flexible — are fabricated inside inert-atmosphere gloveboxes filled with nitrogen or argon, which prevents moisture and oxygen from degrading the perovskite film during deposition. Those controlled environments add significant capital cost and are incompatible with continuous roll-to-roll (R2R) manufacturing, the production method most likely to deliver the large-area, low-cost flexible solar films the market needs. “Air-processed” means the critical interface-engineering step — adding the theanate layer to the tin oxide electron transport layer — works at room temperature in ambient air, without any glovebox requirement. The 2025 ambient-air R2R compatibility review in ACS Applied Materials & Interfaces identified this as the key prerequisite for practical roll-to-roll manufacturing of flexible perovskite cells.
The markets flexible perovskite cells specifically address are those rigid silicon panels cannot serve. Building-integrated photovoltaics (BIPV) — facades, windows, and roofing materials that generate electricity while functioning as architectural surfaces — need lightweight films that conform to curved surfaces. Wearable electronics and IoT sensor nodes need durable bendable power sources. Vehicle-integrated photovoltaics need cells shaped to body panels and rooflines. In each case, a rigid, fragile silicon wafer is not a viable option regardless of its efficiency. The global flexible perovskite solar market was approximately $94 million in 2025, projected to reach $1.08 billion by 2034 per the flexible perovskite market report as these application categories mature.
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