Characterizations and Understanding of Additives Induced Passivation Effects in Narrow-Bandgap Sn-Pb Alloyed Perovskite Solar Cells

Narrow-bandgap Sn-Pb alloyed perovskite solar cells have higher SQ limits than the widely studied lead based perovskites, but they often suffer from more severe energy losses. Pb(SCN)(2) and SnF2 additives were widely used in those narrow-bandgap perovskite solar cells, but the underlying mechanisms were not much understood yet. Here, we employed spatially and time-resolved spectroscopies to investigate the additive effects. We find the SnF2 additive mainly works as morphology modifiers, while Pb(SCN)(2) plays little roles in film formation but significantly alters the charge carriers dynamic especially at grain boundaries and eliminates the density of defect states. A small device with power conversion efficiency (PCE) of 18.1% and fill factor as high as 82.4% were realized by the synergetic effects of SnF2 and Pb(SCN)(2) additives, and a large area mini module device with 15.5% PCE was also successfully demonstrated.