Reduced methylammonium triple-cation Rb_0.05(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

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.