Quaternary Ammonium Additives Enable Efficient and Stable 1.77 eV Wide‐Bandgap Perovskite Solar Cells

ABSTRACT Wide‐bandgap (WBG) inverted perovskite solar cells (PSCs) are a crucial component for tandem solar cells. However, their industrialization is impeded by persistent challenges in achieving high efficiency and long‐term stability. Here, we present the quaternary ammonium salt—tetrabutylammonium tribromide (TBABr 3 ) as an additive that passivates intrinsic defects in the perovskite bulk. The introduced TBABr 3 interacts with undercoordinated Pb 2+ to balance their complexation, while Br 3 − can fill the I − vacancy defects in the bulk phase, thereby reducing defect density and achieving defect passivation, ultimately improving the photostability of the PSCs. The fabricated WBG PSCs achieve a high V OC of 1.327 V and a PCE of 19.34%, which is significantly higher than the control devices. The device stability is also markedly enhanced. When stored in a dark nitrogen environment for 1000 h, the unencapsulated devices retain 90% of their initial efficiency, compared to only 40.1% of the control devices. Additionally, under continuous operation under AM1.5G standard illumination for 300 h, the devices retain 79% of their original efficiency, significantly higher than the 63% retention of the control devices. This defect passivation strategy provides a solution to WBG PSCs stability, bringing the industrialization of tandem solar cells closer to reality.