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

High-performance perovskite solar cells require efficient extraction of photogenerated 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. Perovskite solar cells (PSCs) still suffer from the issue of stability, which is dependent on the photo-induced electronic processes, especially the perovskite-TiO₂ interfacial charge transfer. Here, we report that the perovskite-TiO₂ interplay can be promoted by surface rutilization of anatase TiO₂. The results show that an increment of 50% in power conversion efficiency can be achieved in our hole-conductor-free carbon-based PSCs. Furthermore, by continuously operating at the power-maximum output point in ambient air in the presence of moisture, oxygen, and ultraviolet irradiation, the cells with surface-rutilized anatase TiO₂ exhibit unusually stable power output for as long as 120 hr. Moreover, favorable lattice matching between rutilized TiO₂ and perovskite stabilizes interfacial connectivity upon temperature change. Our configuration meets the criteria for practical application of PSCs. Highly efficient and stable conversion of solar energy to electricity requires the efficient extraction of photogenerated electrons from perovskite to TiO₂. By surface rutilizing anatase, efficient power conversion and long-term (120 hr) stable power-maximum output of perovskite solar cells operated in ambient air in the presence of oxygen, moisture, and UV irradiation can be achieved. The cells can retain their initial performance by repeatedly undergoing high-temperature treatment. These promising results suggest that this configuration meets the criteria for practical application.