Controlling crystallization dynamics of Sn–Pb mixed perovskite films for efficient scalable photovoltaics

Abstract

A critical bottleneck for the upscaling of all-perovskite tandem solar cells is the scalable fabrication of Sn–Pb mixed narrow-bandgap (NBG) perovskite films. In response, this work researches routes to control the crystallization of blade-coated NBG perovskite thin films. Methylammonium chloride (MACl) is introduced as an additive to refine crystallization and optimize perovskite morphology during the vacuum-assisted growth (VAG) as well as the subsequent annealing step. Using in situ photoluminescence analysis, it is shown that MACl enhances the competition of crystal growth during the VAG and retards secondary crystallization during annealing. As a result, grain size, homogeneity, and crystallinity of blade-coated NBG perovskite films are significantly improved, leading to improved reproducibility and device performance. Champion power conversion efficiencies of 20.5% and 19.1% are demonstrated in devices with spin-coated and blade-coated perovskite absorber layers, respectively. In combination with a wide-bandgap (WBG) sub-cell fabricated using the same anti-solvent-free VAG method, a champion all-perovskite tandem solar cell realizes a power conversion efficiency (PCE) of 27.5%. These improvements are attributed to the reduced charge transport losses and enhanced charge extraction in the optimized NBG perovskite absorber. Thereby, this study enables scalable production of high-performance all-perovskite tandem photovoltaics.