Large improvement of photovoltaic performance of flexible perovskite solar cells using a multifunctional phospho-ethanolamine-modified SnO2 layer

The non-radiative recombination loss caused by diverse defects within SnO2 electron transport layer (ETL), perovskite film, and their interface greatly hinders the further improvement of the performance and stability of flexible perovskite solar cells (PSCs). Therefore, it is urgent to develop an effective strategy to address these issues. Herein, a multifunctional material, phospho-ethanolamine (PE), is introduced into SnO2 aqueous colloids to suppress defects and prepare high-quality ETL. The results demonstrate that the incorporation of PE can significantly reduce the number of Sn dangling bonds due to the formation of new Sn—O—P bonds, which is beneficial to ameliorating the electrical properties of SnO2 and obtaining dense SnO2 film. Meanwhile, the amino group (NH2) of PE can interact with uncoordinated Pb2+ in perovskite, thereby suppressing SnO2/perovskite interface defects and obtaining improved perovskite film quality. Consequently, the optimized flexible and rigid PSCs based on the SnO2-PE composite ETL yield outstanding photoelectric conversion efficiency (PCE) of 18.48% and 21.61%, respectively. Moreover, flexible PSCs based on SnO2-PE present excellent mechanical durability, and 90.6% of the original PCE is retained after 1000 bending cycles.