Energetically favored formation of SnO2 nanocrystals as electron transfer layer in perovskite solar cells with high efficiency exceeding 19

Abstract In fabrication of SnO 2 electron transfer layer (ETL) via traditional solution routes, the strong dependence of film crystallization on high temperature annealing or robust thermal treatment makes it challengeable to prepare crystallized SnO 2 ETLs at low temperature ( 2 ETL below 80 °C is realized for the first time. In the new route, participation of atmosphere O 2 and H 2 O by refluxing is crucial as it can greatly promote Sn 2+ oxidation and controlled hydrolysis in SnCl 2 ·2H 2 O alcohol solution, in turn opening up an energetically favorable pathway for SnO 2 crystallization at low temperature. Systematical investigations reveal that SnO 2 ETLs have high conductivity and transmittance and appropriate energy band level, by which PSCs obtain superior photovoltaic performance, with a champion power conversion efficiency (PCE) and steady-state PCE of 19.20% and 18.48% achieved, respectively, much higher than that of the devices using high temperature annealed TiO 2 ETLs (16.61% and 15.03%). The SnO 2 -ETL-based flexible PSCs also attain a high PCE up to 16.11% and among the highest records of flexible PSCs. Due to a larger band gap, SnO 2 -ETLs-based PSCs show superior UV resistance against high intensity UV light irradiation.