Investigation on guanidinium bromide incorporation in methylammonium lead iodide for enhanced efficiency and stability of perovskite solar cells

A guanidinium incorporated double cation mixed halide perovskite was investigated by including guanidinium bromide (GABr) in methylammonium lead iodide (MAPI) under various GABr concentrations. The XRD patterns with characteristic (110), (220) and (310) peaks showed an initial shift towards lower angles and then towards higher angles, indicating an initial lattice expansion and then contraction with increasing GABr content. Increasing the GABr concentration above 10% resulted in reducing the visible absorbance of the compound along with widening of the bandgap. The bandgap increased from 1.58 eV for MAPI to 2.06 eV for 80% GABr but not for 1-10% GABr. Steady state and time resolved photoluminescence measurements revealed that the 10% GABr incorporated samples exhibited higher photoluminescence emission and enhanced charge carrier lifetime than MAPI. The scanning electron microscopy images depicted typical surface passivation effect observed in the GA based additives, where an increase in grain size and low number of pinholes were observed for 10% GABr incorporated films. As an outcome of these synergistic effects, perovskite solar cells (PSCs) fabricated from 10% GABr presented a superior power conversion efficiency (PCE) of 16.70 +/- 0.20% compared to the conventional MAPI (PCE = 15.35 +/- 0.15%). The 10% GABr based PSCs exhibited lesser hysteresis compared to MAPI and retained > 97% of their pristine PCE after 400 h of continuous illumination, while the PCE of MAPI-based PSCs deteriorated with time.