Interfacial Enhancement of Self‐Assembled Monolayer by Thermal Annealing and its Impact on Perovskite Solar Cells

Self-assembled monolayers (SAMs) based on carbazole-phosphonic acids, such as MeO-2PACz, have become the hole-selective contact in high-efficiency inverted perovskite solar cells (PSCs). While spin coating remains the conventional deposition route, vacuum thermal evaporation (VTE) has attracted growing interest as a solvent-free, large-area compatible process, and postdeposition thermal annealing has been employed to further improve interfacial quality. However, how annealing operates across these two fundamentally different deposition pathways has not been systematically examined. Here, we compare MeO-2PACz SAMs prepared by spin coating and by VTE, each with and without postannealing at 100 °C, yielding four sample groups. Ultraviolet photoelectron spectroscopy, X-ray photoelectron spectroscopy, contact-angle, and atomic force microscopy analyses show that, regardless of the deposition method, annealing removes loosely bound overlayer species and promotes covalent InOP anchoring to the indium tin oxide surface, yielding a more favorable energy-level alignment with the perovskite. Resin-assisted peel-off combined with Raman mapping, scanning electron microscopy, and photoluminescence measurements further reveals a more uniform buried hole transport layer/perovskite interface with suppressed nonradiative recombination. Inverted PSCs based on both solution- and vacuum-deposited SAMs consequently exhibit enhanced open-circuit voltage and power conversion efficiency after annealing, establishing postannealing as a shared interfacial-engineering handle across deposition routes.