Tri-functionalized TiO Cl4-2 accessory layer to boost efficiency of hole-free, all-inorganic perovskite solar cells

Tin dioxide (SnO2) is generally regarded as a promising electron-transporting layer (ETL) for state-of-the-art perovskite solar cells (PSCs), however, the ubiquitous oxygen-vacancy-related defects at SnO2 surface and the large energy difference between conduction band of SnO2 and perovskite layer undoubtedly cause severe charge carrier recombination, resulting in sluggish charge extraction efficiency and non-negligible open-circuit voltage (Voc) loss. Herein, a chlorine-containing TiOxCl4-2x accessory layer is fabricated by immersing SnO2 layer into the TiCl4 aqueous solution to passivate the surface oxygen-vacancy-related defects of SnO2 layer and to set an intermediate energy level at ETL/perovskite interface in all-inorganic cesium lead tri-bromine (CsPbBr3) PSCs. Furthermore, the TiOxCl4-2x layer also improves the infiltration of SnO2 layer surface toward perovskite precursor for high-quality perovskite film. Finally, the hole-free, all-inorganic CsPbBr3 PSC with a structure of FTO/SnO2/TiOxCl4-2x/Cs0.91Rb0.09PbBr3/carbon achieves a champion efficiency of 10.44% with a Voc as high as 1.629 V in comparison to 8.31% for control device. Moreover, the optimized solar cell presents good stability in 80% humidity in air.