Effect of the Hammett substituent constant of -substituted benzoic acid on the perovskite/SnO interface passivation in perovskite solar cells.

It is critical to design bifunctional passivation molecules to simultaneously passivate the charge transport layer and perovskite layer at the charge transport layer/perovskite interface in perovskite solar cells (PSCs). In this study, we investigate the effect of -substituted benzoic acid with different Hammett constants () on the photovoltaic performance of PSCs. Two passivation molecules 4-aminomethylbenzoic acid (4-AMBA) and 4-sulfamoylbenzoic acid (4-SABA) are used to passivate the SnO surface with carboxylic acid and the perovskite with -substituent electron-donating -CHNH ( = -0.02) and electron-withdrawing -SONH ( = +0.60). Compared with non-passivated PSC, the passivation improves the power conversion efficiency (PCE) mainly due to the increased open-circuit voltage () and fill factor (FF), where the -SONH substituent is better in improving the photovoltaic performance than the -CHNH one. The trap density is more reduced and the charge extraction ability is more improved by 4-SABA than by 4-AMBA, which indicates that the weak electron-withdrawing nature of a -substituent such as -SONH is better for the passivation of the bottom perovskite than a weak electron-donating -CHNH substituent. Consequently, the passivation with 4-SABA enhances the PCE from 22.27% to 23.64%, along with improved long-term stability. This work highlights for the first time the role of the Hammett constant in the surface passivation of PSCs.