Flexible perovskite solar cells (F-PSCs) offer lightweight, low-cost, and conformable energy solutions. However, their power conversion efficiency (PCE) remains lower than rigid cells, particularly in large-area modules, due to challenges in fabricating uniform, high-quality perovskite films on flexible substrates. Existing research primarily improves large-area film quality through interface and crystallization engineering. All-perovskite tandem structures (combining wide-bandgap and narrow-bandgap perovskites) reduce thermal losses and overcome single-junction efficiency limits. However, research on flexible tandem cells (especially large-area modules) remains limited. High bromine and cesium content in wide-bandgap perovskites, coupled with gas quenching, often leads to poor crystallization and defect introduction. The Millennial Temperature and Humidity Combined Environmental Test Chamber is specifically designed to validate and evaluate the reliability of modules or materials. It achieves rapid temperature cycling to enhance testing efficiency and complies with standards such as IEC 61215 and ISO.

This study proposes a scalable strategy for in-situ additive coating treatment of wet perovskite films under continuous gas quenching. It yields high-quality large-area films, achieving a small-area flexible all-perovskite tandem cell PCE of 27.5%. Large-area modules certified at 23.0% PCE demonstrate excellent stability, narrowing the efficiency gap between flexible and rigid perovskite tandem cells.

Core Value of Flexible Perovskite

Flexible solar panels can be deposited on lightweight substrates like plastic or metal foil, achieving final thicknesses of just a few micrometers. This enables surfaces such as rooftops, curved surfaces, and even clothing to be transformed into energy sources. Furthermore, their extremely low mass provides a significant advantage in “specific power” (power output per unit mass), making them particularly suitable for scenarios demanding stringent “volume-to-weight ratio” requirements, such as spacecraft.

Additive-Assisted In-Situ Scraping Strategy

a. SEM image of WBG on flexible substrate b. Photograph showing color change of perovskite film c. Schematic of additive-assisted in-situ coating strategy d. XRD pattern e. PL spectrum

This study proposes in situ coating with a solution of methylammonium chloride (MACl) and phenethylammonium iodide (PEAI) in isopropanol during the “coating window period” (CW) after gas quenching to remove residual dimethyl sulfoxide (DMSO) and introduce additives that enhance crystal growth and defect passivation. X-ray diffraction (XRD) and steady-state photoluminescence (PL) measurements indicate that MP-CW (MACl/PEAI coating window-treated) films exhibit narrower and more intense diffraction peaks alongside higher PL intensity, demonstrating enhanced crystalline quality and reduced non-radiative recombination.

Mechanism of the in-situ coating strategy

a. Solubility changes b. ToF-SIMS spectra c. Photographs of diffusion and removal d. Surface-sensitive XPS of the 4f core level e. XPS of the buried interface chlorine (Cl) 2p core level

WBG perovskite films readily form buried interface voids on PET substrates, primarily due to high-boiling-point DMSO solvent being trapped beneath the film. Subsequent high-temperature annealing induces volume collapse, creating these voids. The MP-CW strategy utilizes a MACl-promoted Cl-DMSO coordination pathway to enable PEA⁺ ion diffusion to the buried interface for passivation, while simultaneously regulating crystallization kinetics and removing residual DMSO. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) reveals uniform distribution of PEA⁺ signals throughout the entire film layer (including the buried interface) in MP-CW films, whereas single-additive or post-treated samples show signals confined to the surface.

Solubility experiments demonstrate that MACl addition enhances PbX₂ solubility in DMSO, enabling PEAI to deeply penetrate the buried interface. X-ray photoelectron spectroscopy (XPS) further confirmed a shift of the Pb 4f peak toward lower binding energies in MP-CW samples, indicating electrostatic interactions between PEA⁺ and under-coordinated Pb²⁺ ions, thereby achieving deep passivation.

Quality and uniformity of large-area films

a. PL spectra of perovskite films in the control group and MP-CW group b. TRPL spectra of the HTL/perovskite stack c. Two-dimensional PL imaging spectra of the samples d. Statistical histogram of PL peak (intensity) distribution in the samples e. QFLS histogram of the sample on a 6×6 cm² flexible substrate

Film quality was evaluated via steady-state and time-resolved photoluminescence (TRPL) measurements. MP-CW films exhibited high and uniform PL intensity under both front and back excitation, indicating effective suppression of non-radiative recombination. TRPL reveals that the charge extraction lifetime (τ₁) of MP-CW decreases from 63.9 ns to 14.7 ns, while the bulk recombination lifetime (τ₂) increases from 376.3 ns to 1353.3 ns, indicating enhanced interfacial charge transport and reduced bulk defects.

Two-dimensional PL mapping reveals that fluorescence intensity fluctuations in MP-CW films are four times lower than in the control group (409±154 vs. 673±30 counts), demonstrating excellent large-area uniformity. The QFLS distribution is also more concentrated, further validating this uniformity.

Flexible battery performance

Performance and Photovoltaic Characterization of Flexible Perovskite Cells

Using an inverted single-junction cell with the structure PET/ITO/NiOx-SAM/WBG perovskite/C60/ALD-SnO₂/Cu, the optimized MP-CW cell achieved a champion PCE of 18.48% (VOC = 1.356 V, JSC = 16.27 mA cm⁻², FF = 83.74%), surpassing the control group (16.71%). The average PCE of 30 cells approached 18.2%, demonstrating excellent batch consistency. Eight subcells exhibited nearly uniform PCE distribution on a 6×6 cm² substrate, validating the strategy's scalability.

Electroluminescence (EL) testing revealed higher external quantum electroluminescence efficiency (EQEEL) in MP-CW cells, with a calculated ΔVOC of 0.04 V consistent with J-V results. VOC testing under varying light intensities showed the ideal factor decreasing from 1.81 to 1.35, indicating reduced recombination losses. Photoluminescence quantum yield (PLQY) testing revealed the voltage loss (Eloss) in MP-CW films decreasing from 127 meV to 107 meV, demonstrating significant interface passivation effects.

Flexible All-Perovskite Tandem Module

 Photovoltaic Performance and Stability of All-Perovskite Tandem Solar Cells

A flexible all-perovskite tandem structure was constructed based on optimized WBG subcells: PET/ITO/HTL/WBG/composite junction (RBJ)/NBG perovskite/C60/ALD-SnO₂/Cu. The champion tandem cell achieved a PCE of 27.5% (VOC = 2.13 V, JSC = 16.0 mA cm⁻², FF = 80.4%), with an average PCE of 26.5 ± 0.5% across 48 cells.

The module employs a series configuration of 8 subcells, achieving a GFF of 95.8%. The certified module with an aperture area of 20.26 cm² demonstrated a PCE of 23.0% (steady-state efficiency 22.1%), with an active area efficiency exceeding 24%. An average PCE of 22.2±0.5% was achieved across 35 modules, demonstrating excellent reproducibility. Scale-up efficiency loss decreased from 20% to 12%, and uniform crystallization over 804 cm² was achieved on 30×40 cm² PET substrates via pilot-scale slot-die coating.

Mechanical bending tests showed the MP-CW module retained 97.2% of its initial PCE after 10,000 cycles at a 10 mm radius (1% strain), outperforming the control group (79.9%). In light stability testing (ISOS-L-1), the PET-encapsulated MP-CW module achieved T80 of 318 hours, while the glass-encapsulated version reached 715 hours, comparable to rigid laminated modules. During thermal cycling (ISOS-T-3), the MP-CW module retained 80% of its initial PCE after 200 cycles, significantly outperforming the control group (50%).

This study successfully addressed the challenge of large-scale fabrication of high-quality perovskite films on flexible substrates through an innovative “in-situ additive coating + continuous gas quenching” strategy: It achieves high PCE of 27.5% (small cells) and 23.0% (certified modules), while demonstrating exceptional mechanical stability, photostability, and tolerance to extreme environments. Notably, it retains initial performance after 10,000 cycles at a 10 mm bending radius, validating the practical application potential of flexible photovoltaics. This technology not only narrows the efficiency gap between flexible and rigid perovskite tandem cells but also provides a “low-cost, scalable” fabrication solution, laying the foundation for the industrialization of next-generation lightweight solar technologies.

Millennial Temperature and Humidity Combined Environmental Test Chamber

The Millennial Temperature and Humidity Combined Environmental Test Chamber utilizes an imported temperature controller, enabling multi-stage temperature programming with high precision and excellent reliability to meet testing requirements under various climatic conditions.

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▶ Temperature Range: 20°C to +130°C

▶ Temperature & Humidity Range: 10%RH to 98%RH (at +20°C to +85°C)

▶ Complies with Testing Standards: IEC61215, IEC61730, UL1703, and other testing standards

The MillennialTemperature and Humidity Combined Environmental Test Chamber precisely simulates environments for -40°C ↔ 85°C (ISO S-T-3 standard) thermal cycling and stable control test environments. It provides precise extreme environment simulation for flexible all-perovskite tandem modules, enabling stability verification of high-efficiency modules after 1000 hours of damp heat testing and 10,000 bending cycles. This lays the foundation for scaling up high-performance flexible photovoltaic applications based on the in-situ coating strategy for these modules.