In situ coating strategy for flexible all-perovskite tandem modules

Flexible perovskite solar cells offer a platform for lightweight, low-cost and conformable energy solutions. However, their power conversion efficiency (PCE) lags their rigid counterparts, particularly in large-area modules owing to challenges in achieving uniform, high-quality perovskite films on flexible substrates. Here we introduce a scalable fabrication strategy based on retreating the wet perovskite films with an in situ additive coating under continuous gas quenching. This method enables dynamic additive modulation during crystallization, unlocking interfacial and bulk film control that is otherwise inaccessible in after-coating treatments or ink modification strategies. This method yields 30 × 40 cm² wide-bandgap perovskite films on polyethylene terephthalate substrate fabricated under ambient conditions with exceptional crystallinity, low-trap-density and void-free buried interfaces. As a result, we achieve a PCE of 27.5% for a flexible all-perovskite tandem solar cell (area 0.049 cm²) and a certified 23.0% for a large flexible module (area 20.26 cm²) with a geometric fill factor of 95.8%. We also demonstrate industrial scalability by slot-die coating a flexible wide-bandgap perovskite module with an aperture area of ~804 cm² under ambient conditions. These modules retain 97.2% of their initial PCE after 10,000 bending cycles at a 10 mm radius (1% strain) and withstand thermal cycling (−40 °C ↔ 85 °C) and continuous 1-sun illumination. This Article narrows the efficiency gap between flexible and rigid perovskite tandems and establishes a practical route towards scalable, high-performance flexible photovoltaics.