Modification of compact TiO2 layer by TiCl4-TiCl3 mixture treatment and construction of high-efficiency carbon-based CsPbI2Br perovskite solar cells

Abstract In the construction of high performance planar perovskite solar cells (PSCs), the modification of compact TiO2 layer and engineering of perovskite/TiO2 interfaces are essential for efficient electron transfer and retarded charge recombination loss. In this work, a facile and effective strategy is developed to modify the surface of compact TiO2 layer by TiCl4-TiCl3 mixture treatment. Compared with conventional sole TiCl4, the TiCl4-TiCl3 treatment takes the advantage of accelerated and controlled hydrolysis of TiCl3, therefore TiO2 with dominating anatase phase and moderate roughness is obtained to facilitate the growth of CsPbI2Br perovskite layer with high quality. Furthermore, the oxidation-driven hydrolysis of TiCl3 component results in surface Cl doping that facilitates interfacial electron transfer with retarded recombination loss. The average power conversion efficiency (PCE) of carbon-based CsPbI2Br planar PSCs based on TiCl4-TiCl3 treatment increases to 14.18% from the intial 13.04% based on conventional sole TiCl4 treatment. The champion PSC exhibits a PCE of 14.46% (Voc = 1.28 V, Jsc = 14.21 mA/cm2, and FF = 0.794), which is one of the highest PCEs for carbon-based CsPbI2Br PSCs.