Incremental Feeding of Perovskite Powders: Angstrom-Precision Growth for Single-Source Solar Cell Fabrication.

Vacuum-based deposition of halide perovskites receives a lot of attention for its proven scalability and conformal depositions. Co-evaporation has remarkable success, but efficiencies continue to lag behind their solution-based counterparts. This is in part attributed to the complex sublimation behavior of some organic ammonium precursor salts and the increased complexity of the absorber materials, requiring the use of four or more sources in a conventional co-evaporation setup. The latter has driven work into single-source methods with flash evaporation presented as one such method. However, flash evaporation processes typically evaporate all material in a single batch, leading to short deposition times at high temperatures. Particle sputtering effects seen at these high temperatures drive processes toward low temperatures where prolonged exposure causes degradation. Here, a pulse-driven incremental powder feeding system is presented. This method is capable of stable flash evaporation rates for >1 h, with controlled rates as low as 1.5 Å per pulse (±0.89). The feasibility of this method is demonstrated for three different perovskite compositions: FAPbBr₃, MAPbI₃, and FA_1-xMA_xPbSnI₃:SnF₂. Furthermore, FAPbBr3 and MAPbI₃ are integrated into all vacuum-processed thin-film solar cells leading to power conversion efficiencies (PCE) of ~4% and 10%, respectively. [ABSTRACT FROM AUTHOR]