Lead halide-templated crystallization of methylamine-free perovskite for efficient photovoltaic modules

Upscaling efficient and stable perovskite layers is one of the most challenging issues in the commercialization of perovskite solar cells. Here, a lead halide-templated crystallization strategy is developed for printing formamidinium (FA)-cesium (Cs) lead triiodide perovskite films. High-quality large-area films are achieved through controlled nucleation and growth of a lead halide_N-methyl-2-pyrrolidone adduct that can react in situ with embedded FAI/CsI to directly form alpha-phase perovskite, sidestepping the phase transformation from delta-phase. A nonencapsulated device with 23% efficiency and excellent long-term thermal stability (at 85 degrees C) in ambient air (similar to 80% efficiency retention after 500 hours) is achieved with further addition of potassium hexafluorophosphate. The slot die-printed minimodules achieve champion efficiencies of 20.42% (certified efficiency 19.3%) and 19.54% with an active area of 17.1 and 65.0 square centimeters, respectively.

Automated summary

Efficient and stable perovskite layers are crucial for the commercialization of perovskite solar cells. A lead halide-templated crystallization strategy has been developed to print formamidinium-cesium lead triiodide perovskite films, achieving high-quality large-area films with controlled nucleation and growth. An unencapsulated device with 23% efficiency and excellent long-term thermal stability has been achieved, showcasing the potential for practical application in the future.