Role of GeI2 and SnF2 additives for SnGe perovskite solar cells

The distribution of trap states within perovskite vicinity or hetero-interfaces is the prime attribution towards carrier dynamics inferiority and low photovoltaic performances. In this work, thermally stimulated current (TSC) is performed to unravel the impact of germanium (Ge) addition in passivating and reducing trap states; consequently, to improve its carrier dynamics. The addition of 5 mol% germanium into the FA(0.75)MA(0.25)Sn(1-x)Ge(x)I(3) (FMSGI(5)) framework strikingly suppresses the trap density from 10(15) - 10(17) cm(-3) (without Ge) to 10(8) -10(14) cm(-3), thereby renders longer charge diffusion length (similar to 1 mu m) and lifetime; coupled with excellent charge mobility and efficiency of 7.9%. Interestingly, the FMSGI(5) perovskite exhibits indistinguishable trap densities profile from that of MAPbI(3) perovskite and exhibits a long charge diffusion length of 1 mu m. Another important information to be highlighted in this paper is the advantage of SnF2 to subside the vacancy of Sn2+. This study provides deep intuitive on trap landscape, which unlocks opportunities for the designation of high performance lead-free perovskite solar cells.