Bifunctional Passivation through Fluoride Treatment for Highly Efficient and Stable Perovskite Solar Cells

Abstract Due to the low formation energy, surface defects are more likely to form on the surface of TiO 2 films, resulting in a decline in the efficiency and stability of perovskite solar cells (PSCs). Additionally, defects on the bottom surface of the perovskite layer in contact with TiO 2 play a key role in V oc (open circuit voltage) loss and the PSC degradation process. Therefore, to improve the efficiency and stability of PSCs, it is critical to develop a reproducible and low‐cost method for passivating the defects on both the TiO 2 surface and on the bottom surface of the perovskite layer. In this work, fluoride is utilized as a bifacial contact passivation agent for decreasing the number of defects on the TiO 2 surface and the bottom surface of the perovskite layer. PSC efficiency can be significantly increased from 21.3% to 23.7% with fluoride passivation. In addition, the long‐term stability of PSCs, especially light irradiation stability, can be markedly improved. The passivation effects of fluoride treatment on TiO 2 films are studied by theoretical calculation and experimental characterization. This work provides a thorough understanding of the TiO 2 /perovskite interface and demonstrates an approach for improving the efficiency and stability of PSCs.