A Complementary Hole‐Transport Layer of PTAA and SAM on FTO Substrate for p‐i‐n Structured Perovskite Solar Cells

Abstract The quality of thin films produced by solution‐based approaches is highly influenced by the substrates. Fluorine‐doped tin oxide (FTO) glass is one of the most promising substrates for the commercialization of perovskite solar cells (PSCs). However, achieving optimal shunting and series resistances, as well as ensuring energetically homogeneous coverage of the hole transport layer (HTL) on FTO substrates remains challenging. Here, a strategy is developed that combines the advantages of two most popular HTL materials, i.e., Poly[bis(4‐phenyl)(2,4,6‐trimethylphenyl)amine (PTAA) and self‐assembly monolayer (SAM), and reveals their complementary effects. The PTAA is preferentially deposited in the valleys of the FTO substrate, while the SAM occupied the peaks where PTAA coverage is absent, leading to an improved uniformity of surface energy. Assisted by additional copolymer surfactants adjusting the perovskite precursor wetting on substrates, the fabricated PSCs based on the composite PTAA:SAM HTL demonstrate 25.4% power conversion efficiency with significantly improved reproducibility. The unencapsulated devices retain 100% of their initial efficiency after 1000 h of light soaking under AM 1.5 g illumination, providing a novel strategy for developing highly reproducible p‐i‐n PSCs based on FTO substrates.