Laser-Assisted Ultrafast Fabrication of Crystalline Ta-Doped TiO 2 for High-Humidity-Processed Perovskite Solar Cells.

A titanium dioxide (TiO 2 ) compact film is a widely used electron transport layer (ETL) for n-i-p planar perovskite solar cells (PSCs). However, TiO 2 sufferers from poor electrical conductivity, leading to high energy loss at the perovskite/ETL/transparent conductive oxide interface. Doping the TiO 2 film with alkali- and transition-metal elements is an effective way to improve its electrical conductivity. The conventional method to prepare these metal-doped TiO 2 films commonly requires time-consuming furnace treatments at 450-600 °C for 30 min to 3 h. Herein, a rapid one-step laser treatment is developed to enable doping of tantalum (Ta) in TiO 2 (Ta-TiO 2 ) and to simultaneously induce the crystallization of TiO 2 films from its amorphous precursor to an anatase phase. The PSCs based on the Ta-TiO 2 films treated with the optimized fiber laser (1070 nm) processing parameters (21 s with a peak processing temperature of 800-850 °C) show enhanced photovoltaic performance in comparison 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 power conversion efficiencies (PCEs) of 18.34% and 16.04% for devices based on Cs 0.1 FA 0.9 PbI 3 and CH 3 NH 3 PbI 3 absorbers, respectively. These results are due to the improved physical and chemical properties of the Ta-TiO 2 films treated by the optimal laser process in comparison to those for the furnace process. The laser process is rapid, simple, and potentially scalable to produce metal-doped TiO 2 films for efficient PSCs.