Grain growth study of perovskite thin films prepared by flash evaporation and its effect on solar cell performance

Abstract

Flash evaporation is a vacuum-based evaporation method that is particularly suitable to prepare perovskite films for solar cell devices. Growth pressure has been found to be a critical parameter for perovskite film growth. The transport-determined growth mechanism is discussed in detail. The dense MAPbI₃ films can be achieved only under a low growth pressure of 5 × 10⁻³ Pa, while a rough surface covered by step-like grains and voids is found for MAPbI₃ films grown under a high Ar pressure of 10 Pa. In addition, we found that the presence of PbI₂ phase in the perovskite films could suppress the growth of the grain size; by using precursors with a high MAI/PbI₂ ratio, evaporated MAPbI₃ films with grain sizes larger than 500 nm can be achieved. The average power conversion efficiency of the perovskite solar cells increased from 1.82% to 10.01% with increasing grain size, indicating the universal importance of controlling the perovskite grain size for the performance improvement of solar cells based on both solution and evaporated perovskite films.