Tri-functionalized TiOxCl4-2x accessory layer to boost efficiency of hole-free, all-inorganic perovskite solar cells

Tin dioxide (SnO 2 ) 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 SnO 2 surface and the large energy difference between conduction band of SnO 2 and perovskite layer undoubtedly cause severe charge carrier recombination, resulting in sluggish charge extraction efficiency and non-negligible open-circuit voltage ( V oc ) loss. Herein, a chlorine-containing TiO x Cl 4-2 x accessory layer is fabricated by immersing SnO 2 layer into the TiCl 4 aqueous solution to passivate the surface oxygen-vacancy-related defects of SnO 2 layer and to set an intermediate energy level at ETL/perovskite interface in all-inorganic cesium lead tri-bromine (CsPbBr 3 ) PSCs. Furthermore, the TiO x Cl 4-2 x layer also improves the infiltration of SnO 2 layer surface toward perovskite precursor for high-quality perovskite film. Finally, the hole-free, all-inorganic CsPbBr 3 PSC with a structure of FTO/SnO 2 /TiO x Cl 4-2 x /Cs 0.91 Rb 0.09 PbBr 3 /carbon achieves a champion efficiency of 10.44% with a V oc 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.