FAPbBr3 perovskite solar cells with VOC over 1.5 V by controlled crystal growth using a tetramethylenesulfoxide

Perovskite solar cells (PSC) capable of open-circuit voltage (VOC) over 1.5 V was fabricated based on a formamidinium lead-bromide (FAPbBr3) perovskite absorber film prepared by sequential deposition procedure using dimethylsulfoxide (DMSO) and tetramethylenesulfoxide (TMSO) mixed solvent. A PbBr2 film formed from a precursor PbBr2 solution with the DMSO–TMSO mixed solvent was reacted with FABr to convert into FAPbBr3 film. The mixed solvent-based PbBr2 film exhibits as an amorphous-like phase containing a PbBr2–TMSO complex, which led to formation of an FAPbBr3 film possessing high crystallinity and uniform thick absorber layer compared with the pristine PbBr2 film prepared by pure DMSO solvent. With a bandgap of 2.1 eV, FAPbBr3-based PSCs prepared by the solution process with PbBr2–TMSO complex exhibited high VOC up to 1.55 V and power conversion efficiency of 7.8% on the device fabrication using a Li-treated mesoporous TiO2 as electron transport layer with 5 x 5 mm2 cell active area.