Low temperature solution-derived TiO ₂ -SnO ₂ bilayered electron transport layer for high performance perovskite solar cells

Planar lead halide perovskite solar cells have shown a promising application in the field of printable solar cells. However, high-performance planar perovskite solar cells typically need a high-temperature process to achieve crystallized titanium oxide films as the electron transport layers, which hinders their application in flexible plastic substrates. Here, we demonstrate a bilayered TiO ₂ -SnO ₂ film as an excellent substitute for electron transport layer using a low temperature liquid phase method. The bilayered TiO ₂ -SnO ₂ film exhibits efficient electron extraction and hole blocking ability even at a low processing temperature of 150 °C. The as-obtained solar cells exhibit a champion power conversion efficiency of 18.85% (V _oc = 1.100 V, J _sc = 22.52 mA cm ⁻² and FF = 0.761) under one sun illumination, which is much higher than the devices based on individual SnO ₂ or TiO ₂ electron transport layers. The higher electron extraction driving force at the SnO ₂ /perovskite interface and the stronger hole blocking ability due to the defect-free physical contact at the TiO ₂ /FTO interface are suggested to be the main reasons for the improved device performance.