Highly efficient and stable perovskite solar cells enabled by a fluoro-functionalized TiO2 inorganic interlayer

Summary Interfacial engineering has been commonly used as an effective strategy to enhance device performance and stability of perovskite solar cells (PSCs). However, most of the materials used for interface engineering are based on organics, which may have concerns for the device's long-term stability. Therefore, we developed robust fluoro-terminated TiO2 nanosheets (F-TiO2 NSs) to work as interlayers between perovskite and electron-transporting layers in inverted PSCs. The flat NS morphology of F-TiO2 NSs enables close contact with perovskite with abundant surface fluoro groups, which can interact with undercoordinated lead and MA/FA ions to prevent the formation of cation vacancies and alleviate surface defects. As a result, a remarkable power conversion efficiency (PCE) of 22.86% can be achieved. The operational stability of devices with F-TiO2 NSs interlayers is also enhanced, which can maintain over 90% of their initial PCEs after being monitored at the maximum power point (MPP) for 1,000 h under day/night cycles.