Vacuum preparation of charge transport layers for perovskite solar cells and modules

The successful large-scale fabrication of perovskite solar modules at the square meter level represents a significant milestone in the industrialization process of perovskite photovoltaic technology. In the fabrication of perovskite solar modules, cost-effective solution-based methods are commonly employed for the preparation of the perovskite layer due to their ability to ensure film uniformity with a thickness of approximately 500 nm. However, achieving uniformly coated charge transport layers (CTLs) at square meter levels using solution methods remains a formidable challenge due to the ultrathin nature of the CTLs, which is a few tens of nanometers thick. The fulfillment of this requirement necessitates the exclusive utilization of vacuum deposition technology for CTL preparation. This review focuses on vacuum deposition methods, including magnetron sputtering, atomic layer deposition, electron-beam evaporation, thermal evaporation, chemical vapor deposition and pulsed laser deposition for the fabrication of CTLs in perovskite solar cells and modules. We highlight the advantages and drawbacks of various deposition techniques, while summarizing the CTLs that can be deposited via each method, encompassing thin film characteristics and optimization strategies. Finally, we conclude with some perspectives and challenges for future research on vacuum methods for CTLs in perovskite solar cells.