Ultrasonic Spray-Coated Mixed Cation Perovskite Films and Solar Cells

A solar absorber composed of mixed cation perovskite films containing methylammonium (MA) and formamidinium (FA) lead triiodide (MA_1-xFA_xPbI₃) was prepared by continuous ultrasonic spray-coating. This process combined features of substitutional modifications in perovskites and simple yet versatile processing to realize scalable fabrication. Herein, simultaneous growth from a precursor solution with controlled MA/FA stoichiometry in the inverted perovskite solar cells based on MA_1-xFA_xPbI₃ was systematically investigated to link the thin film quality, optical properties, and crystal structures with photovoltaic performance. The result of the inherent advantages of increased photoabsorption, better film quality, and enhanced crystallinity, the perovskite solar cell composed of the MA_0.75FA_0.25PbI₃ (x = 0.25) perovskite achieved an optimum power conversion efficiency (PCE) as high as 15.61% and an average PCE of 15.15 ± 0.45%. In particular, the spray-deposited MA_0.75FA_0.25PbI₃ unencapsulated cells exhibited almost no hysteresis in the current density-voltage (J-V) curve and excellent long-term stability under ambient conditions (25 °C, 30-40% relative humidity). These results highlight the importance of choosing a suitable mixed cation perovskite composition and scalable spraying technique for high-throughput manufacturing of perovskite solar cells to prolong device lifetime and achieve good reproducibility.