Mixed-solvent-vapor annealing of perovskite for photovoltaic device efficiency enhancement

The key to improve the photovoltaic performance of perovskite solar cells is the quality of perovskite materials. Here, we report a growth mode that the perovskite precursor film is thermal annealed in mixed anti-solvent (IPA) and solvent (DMF) (100:1, v/v) vapor environment to improve the film quality, which enhances the power conversion efficiency of CH3NH3PbI3 based planar heterojunction solar cell device from 12.2% to 15.1%. After 8 days’ storage without encapsulation, the devices retained about 75% of their original efficiency while devices without solvent annealing reduced to 40% of that. It should be mentioned that by further applying compositional engineering such as using CH3NH3PbI3−xClx perovskite precursor and using interface engineering approach, the efficiency of planar heterojunction solar cell could be further enhanced up to 18.9%. The enhancement in photovoltaic performance and stability is due to the perovskite film quality improvement, with the increased average grain size and crystallinity of perovskite.