Surface Rutilization of Anatase TiO2 for Efficient Electron Extraction and Stable Pmax Output of Perovskite Solar Cells

High-performance perovskite solar cells require efficient extraction of photo-generated electrons from the light absorber to the semiconductor skeleton, which can simultaneously stabilize the photovoltaic device by kinetically suppressing superoxide-intermediated degradation by reducing the accumulation of electrons in the perovskite layer. Here, we propose to improve and stabilize the photovoltaic performance of the cells by modulating the surface structures of TiO2. The transformed rutilized phase not only bridges the perovskite-TiO2 interfacial charge transfer but also protects the light absorber from ultraviolet- induced degradation by suppressing the survival of holes generated in the TiO2 skeleton. As a result of these merits, an increment of 50% in power conversion efficiency can be achieved. Furthermore, these cells exhibit extraordinary stability under continuous (120 hr) power-maximum output without cell encapsulation in the presence of moisture, oxygen, and ultraviolet irradiation and can restore to their initial photovoltaic performance by repeatedly undergoing tetragonal-to-cubic phase transition of the perovskite.