Efficient Yttrium(III) Chloride-Treated TiO2 Electron Transfer Layers for Performance-Improved and Hysteresis-Less Perovskite Solar Cells

Hybrid organic-inorganic metal halide perovskite solar cells have attracted widespread attention, owing to their high performance, and have undergone rapid development. In perovskite solar cells, the charge transfer layer plays an important role for separating and transferring photogenerated carriers. In this work, an efficient YCl3-treated TiO2 electron transfer layer (ETL) is used to fabricate perovskite solar cells with enhanced photovoltaic performance and less hysteresis. The YCl3-treated TiO2 layers bring about an upward shift of the conduction band minimum (E-CBM), which results in a better energy level alignment for photogenerated electron transfer and extraction from the perovskite into the TiO2 layer. After optimization, perovskite solar cells based on the YCl3-treated TiO2 layers achieve a maximum power conversion efficiency of about 19.99% (19.29% at forward scan) and a steady-state power output of about 19.6%. Steady-state and time-resolved photoluminescence measurements and impedance spectroscopy are carried out to investigate the charge transfer and recombination dynamics between the perovskite and the TiO2 electron transfer layer interface. The improved perovskite/TiO2 ETL interface with YCl3 treatment is found to separate and extract photogenerated charge rapidly and suppress recombination effectively, which leads to the improved performance.