Co-evaporated oriented DMA_1-xCs_xPbI₃ perovskite films for photovoltaics

Thermally evaporated cesium lead triiodide (CsPbI₃) is a frontier research direction for perovskite-silicon tandem solar cells because of the matching bandgap and good conformality with textured silicon. However, the random orientation and small grains for the co-evaporated CsPbI₃ thin films fabricated at low temperature, resulting in harmful defects and non-radiative recombination. Here, dimethylammonium iodide (DMAI) is introduced into the co-evaporation system at a substrate temperature of 50 °C to prepare preferentially oriented DMA_0.06Cs_0.94PbI₃ film with less defects and enhanced humidity stability. The bandgap also can be reduced from 1.76 eV (γ-CsPbI₃) to 1.73 eV. The p-i-n photovoltaic device based on this film achieves an efficiency of 16.10% with suppressed non-radiative recombination, rivaling with the thermally evaporated wide-bandgap CsPbI₃ solar cells prepared at a high temperature (∼ 350 °C). This in-situ evaporated alloying strategy can pave the way for the crystallization and defect control during perovskite co-evaporation.