Selective reactivity-assisted sacrificial additive coating for surface passivation of wide bandgap perovskite solar cells with cesium tetrafluoroborate

Perovskite solar cells (PSCs) have garnered tremendous attention in recent years due to their exceptional performance and potential for commercialization. PSCs with wide-bandgap (WBG) perovskites are particularly attractive for use in tandem solar cells with existing photovoltaic technologies such as silicon and Cu(In, Ga)Se2. Defect passivation of the surface and grain boundaries of perovskite films is essential to improve the performance of PSCs; however, the choice of agents for surface passivation by a solution process is often limited because of the lack of an orthogonal solvent that does not damage the underlying perovskite. This study proposes a novel approach, selective reactivity-assisted sacrificial additive coating (SSC), to passivate the surface of WBG perovskites. Coating a sacrificial additive salt containing BF4- anions, the method utilizes the selective reaction between the Cs+ cation and BF4- anion to form CsBF4, which passivates the perovskite surface as revealed by the density functional theory calculations. Phenethylammonium tetrafluoroborate is applied to create CsBF4, which improves the open circuit voltage of the devices. The results demonstrate that SSC is a promising approach to passivating the surface of WBG perovskites and can be adapted to other perovskites of various compositions. A novel method, named "selective reactivity-assisted sacrificial additive coating", allowed the BF4- from the sacrificial additive to react selectively with the Cs+ from the perovskite, forming CsBF4 to passivate the A-site vacancy on the surface.