Less is more: Enabling Solvent-Free Fabrication of Perovskite Solar Cells via Thermal Evaporation of Ultrathin Self-Assembled Monolayers

This study explores the feasibility of employing vacuum-deposited organic hole transport layers (HTLs) based on self-assembled monolayer materials, such as MeO-2PACz, in perovskite single-junction solar cells. A key challenge arises from the thermal degradation of these compounds during evaporation, which can impair device performance. To address this, we investigate the influence of thermal exposure in the crucibles during deposition by comparing vacuum-evaporated and spin-coated HTLs, the latter being a laboratory-scale method unsuitable for industrial upscaling. Our results show that repeated thermal evaporation cycles lead to performance losses, likely due to molecular decomposition of the organic material. By lowering the evaporation rate and reducing the layer thickness to as little as one nanometer, thermal exposure is significantly minimized. Optimized deposition parameters yield perovskite solar cells with performance metrics comparable to, or surpassing, those of spin-coated reference devices. Furthermore, we demonstrate solvent-free solar cell fabrication without additional wet-chemical processing steps, achieving promising results. These findings offer valuable insights into scaling deposition processes for self-assembled monolayers, paving the way for efficient, large-area fabrication of perovskite solar cells, also on textured substrates.