Reduced methylammonium triple-cation Rb0.05(FAPbI3)0.95(MAPbBr3)0.05 perovskite solar cells based on a TiO2/SnO2 bilayer electron transport layer approaching a stabilized 21% efficiency: the role of antisolvents

Abstract

Due to their high efficiency and stability, triple-cation based perovskite solar cells (PSCs) have now crossed 23% power conversion efficiency (PCE). However, the perovskite composition and type of the electron transport layer (ETL) play a key role in improving their performance. Therefore, in the present investigation, high quality TiO₂/SnO₂ bilayer ETLs and thermally stable reduced methylammonium (MA) cation based triple-cation perovskite layers are used to fabricate thermally stable PSCs. By retaining their normal (n–i–p) device architecture, the influence of antisolvents on the perovskite layer has been investigated in detail. Systematic studies in this work reveal that the amorphous SnO₂/TiO₂ bilayer and the trifluorotoluene (TFT) processed perovskite layer significantly influence the current density and open circuit voltage (V_OC) and reduce the charge recombination of perovskite devices. The optimised devices having micrometer size grains exhibited >20.5 ± 0.5% PCE for a thermally stable Rb_0.05(FAPbI₃)_0.95(MAPbBr₃)_0.05 perovskite composition with a SnO₂/TiO₂ bilayer ETL. Furthermore, the SnO₂:TiO₂ bilayer ETL-containing PSCs are thermally stable for more than 200 hours at 80 °C.