Tuning Self‐Assembly of Hole‐Selective Monolayers for Reproducible Perovskite/Silicon Tandem Solar Cells

Abstract Self‐assemble monolayers (SAMs) have become state‐of‐the‐art hole‐selective contacts for high‐efficiency perovskite‐based solar cells due to their easy processing, passivation capability, and low parasitic absorption. Nevertheless, for the deposition of SAMs with a monolayer thickness and a high packing density on metal oxide substrates, critical challenges persist. To overcome these, the study focuses on the impact of annealing temperature – an intrinsic yet so far unexplored process parameter – during the formation of SAMs. By performing in situ angle‐resolved X‐ray photoelectron spectroscopy combined with advanced data analysis routines, it is revealed that increasing the annealing temperature reduces the formed SAM layer thickness from a multilayer stack of ≈5 nm at 100 °C (conventional temperature employed in literature) to a monolayer at 150 °C. Furthermore, denser adsorption of the SAM to the metal oxide surface is promoted at high temperatures, which enhances the interfacial SAM/perovskite passivation quality. With this strategy, a 1.3% abs power conversion efficiency ( PCE ) increment is obtained in fully‐textured perovskite/silicon tandem solar cells, with improved reproducibility, and a champion device approaching 30% PCE . This study advances the understanding of SAMs formation and presents a promising strategy for further progress in high‐efficiency perovskite‐based solar cells.