Orotic Acid as a Bifunctional Additive for Regulating Crystallization and Passivating Defects toward High-Performance Formamidinium–Cesium Perovskite Solar Cells

Formamidinium-cesium (FA-Cs) perovskites are an attractive candidate for perovskite solar cells (PSCs) with high stability, but they tend to suffer from high intrinsic defect density, especially at grain boundaries. Herein, a common heterocyclic conjugated molecule, orotic acid (ORO), was employed as a novel bifunctional additive to simultaneously achieve crystallization regulation and defect passivation of an FA-Cs perovskite toward efficient and stable PSCs. ORO was introduced to an FA-Cs perovskite precursor solution as an effective coordination-induced crystallization regulator to improve the grain size and crystallinity. Furthermore, under the assistance of π electrons, its carboxyl group bonded with undercoordinated Pb2+ defects at grain boundaries, and it was also able to form hydrogen bonds with undercoordinated I- defects, thus significantly reducing defect density. The average power conversion efficiency of the produced PSC devices with the ORO additive was promoted from 17.81% for the control PSCs to 19.32%, and a champion efficiency of 20.62% with negligible hysteresis was achieved. Additionally, the optimized devices exhibited high resistance to moisture incursion, leading to decent environmental stability. This work provides a convenient yet efficient approach to improve crystallization and passivate defects toward PSCs with enhanced efficiency and stability.