TiO2 surface oxygen vacancy passivation towards mitigated interfacial lattice distortion and efficient perovskite solar cell

It is known that there exist inherent oxygen vacancies which is reported to be negative to PSCs performance on the TiO2 film surface where contacts the gaseous phase while the manufacturing process. In this work, we clarified the role of surface oxygen vacancy on TiO2/perovskite interface structure, which would not only serve as trap states to capture generated electrons, but also cause perovskite crystal distortion and PbI bond broken due to the interfacial interaction, generating additional interfacial defects. In addition, by analyzing the interfacial carrier transport routes, the common reason behind the different carrier loss pathways was ascertained to be the oxygen vacancy. Hence, for reducing oxygen vacancies and its negative impact on the device performance, the surface passivation method with gaseous fluorine was proposed, both the DFT (density functional theory) calculation results and experimental approaches proved that the surface passivation method could effectively reduce the traps states, mitigate interface structure distortion and enhance the interfacial charge transfer. As a consequence, MAPbI3-based PSCs with surface passivation obtained a champion PCE of 20.43%, 7.7% higher than that (18.98%) of control device, and FA0.15MA0.85PbI3-based PSCs with surface passivation obtained a champion PCE of 21.16%, 6.2% higher than that (19.92%) of control device.