Vacuum‐Assisted Deposition of Highly Hydrophobic Self‐Assembled Monolayer for High‐Efficiency Perovskite Solar Cells

Recently, various carbazole‐based self‐assembled monolayers (SAMs) have been investigated for use in the hole transport layer (HTL) of perovskite solar cells (PSCs). In particular, [4‐(3,6‐dimethyl‐9H‐carbazol‐9‐yl)butyl] phosphonic acid (Me‐4PACz) is attracting attention as an HTL for high‐efficiency PSC due to its potential for high open‐circuit voltage ( V OC ) and fill factor (FF). However, Me‐4PACz has strong hydrophobicity due to its methyl group (–CH 3 ) and long alkyl chain (C4H 8 ), which makes it difficult to deposit a high‐quality perovskite layer on top of conventionally coated Me‐4PACz. In this study, to overcome these limitations, a new SAM deposition method based on a vacuum‐assisted deposition (VD) process is attempted. As a result, a uniform perovskite layer is deposited on top of Me‐4PACz through a very simple VD process, achieving 20.31% efficiency, which is not only close to the highest efficiency among Me‐4PACz‐based PSCs, but also improved long‐term stability of the device. It is believed that the findings of this study can be a cornerstone for using SAM‐based HTL with high hydrophobicity in the future.