Laser-assisted ultrafast fabrication of crystalline Ta-doped TiO2 for high-humidity processed perovskite solar cells

Titanium dioxide (TiO2) compact film is a widely used electron transport layer (ETL) for n-ip planar perovskite solar cells (PSCs). However, TiO2 sufferers from poor electrical conductivity, leading to high energy loss at the perovskite/ETL/transparent conductive oxide interface. Doping TiO2 film with alkali and transition metal elements is an effective way to improve its electrical conductivity. The conventional method to prepare these metal-doped TiO2 films requires commonly time-consuming furnace treatments at 450-600 ℃ for 30 min to 3 h. Herein, a rapid one-step laser treatment is developed to enable doping of tantalum (Ta) in TiO2 (Ta-TiO2) and to simultaneously induce the crystallization of TiO2 films from its amorphous precursor to anatase phase. The PSCs based on the Ta-TiO2 films treated with the optimized fiber laser (1070 nm) processing parameters (21s with a peak processing temperature of 800–850 °C) show enhanced photovoltaic performance compared to that of the device fabricated using furnace-treated films at 500 °C for 30 min. The ambient-processed planar PSCs fabricated under high relative humidity (RH) of 50-70%, display the power conversion efficiencies (PCEs) of 18.34% and 16.04% for devices based on Cs0.1FA0.9PbI3 and CH3NH3PbI3 absorbers, respectively. These results are due to improved physical and chemical properties of the Ta-TiO2 films treated by the optimal laser process than the furnace process. The laser process is rapid, simple, and potentially scalable to produce metal-doped TiO2 films for efficient PSCs.