Functional polymer passivating FA_0.85PEA_0.15SnI₃ for efficient and stable lead-free perovskite solar cells

Due to their excellent advantages such as low toxicity, superior optoelectronic properties, low-temperature fabrication, and cost-effectiveness, Sn-based perovskites have become the most promising alternatives for high performance lead-free perovskite solar cells. However, the character of Sn²⁺ is easily oxidized to Sn⁴⁺, causing unnecessary p-type self-doping and high leakage current. More seriously, trap-induced non-radiative recombination from rapid crystallization causes into large energy loss with a low open circuit voltage. Therefore, the Sn-based solar cells have efficiency far behind the Pb-based solar cells. Herein, the polymer poly(ethylene glycol) diacrylate (PEGDA) is used to control crystal growth and passivate the defects in FA_0.85PEA_0.15SnI₃ thin film. This Sn-perovskite layer shows compact crystal with large grain size and reduced defects. Optimized perovskite thin film is further processed to fabricate the inverted solar cell with device structure of ITO (indium tin oxide)/PEDOT:PSS (Poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate))/FA_0.85PEA_0.15SnI₃/ICBA (indene-C60 bisadduct)/BCP (bathocuproine)/Ag, which shows the power conversion efficiency (PCE) of 11.45% with voltage of 0.82 V. Moreover, corresponding perovskite solar cells exhibit an enhanced stability due to PEGDA induced compressive strain in perovskite. This work could shed light on one of successful attempts to improve Sn-based solar cell efficiency for sustainable energy conversion.