Defective TiO₂ with high photoconductive gain for efficient and stable planar heterojunction perovskite solar cells

Formation of planar heterojunction perovskite solar cells exhibiting both high efficiency and stability under continuous operation remains a challenge. Here, we show this can be achieved by using a defective TiO₂ thin film as the electron transport layer. TiO₂ layers with native defects are deposited by electron beam evaporation in an oxygen-deficient environment. Deep-level hole traps are introduced in the TiO₂ layers and contribute to a high photoconductive gain and reduced photocatalytic activity. The high photoconductivity of the TiO₂ electron transport layer leads to improved efficiency for the fabricated planar devices. A maximum power conversion efficiency of 19.0% and an average PCE of 17.5% are achieved. In addition, the reduced photocatalytic activity of the TiO₂ layer leads to enhanced long-Term stability for the planar devices. Under continuous operation near the maximum power point, an efficiency of over 15.4% is demonstrated for 100 h.