High-efficiency and ultraviolet stable carbon-based CsPbIBr₂ solar cells from single crystal three-dimensional...

TiO₂ is commonly used to prepare electron transport layers (ETLs) in perovskite solar cells (PSCs). However, conventional TiO₂ ETLs suffer from low electron mobility and charge recombination. Here, we report the direct growth of TiO₂ ETLs on fluorine doped conductive (FTO) glasses with titanium tetrafluoride (TiF₄) as the reactant by hydrothermal method. The TiO₂ ETLs have pure anatase phase, single crystal structure and three-dimensional (3D) nanoarrays morphology. This 3D-TiO₂ ETLs mainly consist of thermodynamically stable surfaces {101} and more reactive surfaces {001}. Compared with the conventional TiO₂ ETLs, the 3D-TiO₂ ETLs can effectively optimize energy level matching and charge transfer dynamics. The special morphology of 3D-TiO₂ ETLs can well assist to form high quality CsPbIBr₂ with larger crystal grains. The champion CsPbIBr₂ PSC with 3D-TiO₂ ETL achieves an efficiency as high as 10.65%, which is equal to the one with hole-transport and Au electrode structure (10.79%) and much higher than the pristine one (7.16%) with the conventional TiO₂ ETL. Furthermore, the 3D-TiO₂ ETLs show ultraviolet (UV) shielding function, which can effectively overcome the UV instability defect of conventional TiO₂ ETLs and obviously enhance UV stability of CsPbIBr₂ and the corresponding PSCs. Therefore, the 3D-TiO₂ ETLs can be good candidates for preparing high-efficiency and UV stable carbon-based CsPbIBr₂ PSCs.