Interfacial Engineering Strategies of Self-Assembled Monolayers for Inverted Perovskite Solar Cells

Inverted perovskite solar cells (PSCs), or p-i-n PSCs, have become increasingly attractive for high-performance perovskite photovoltaics owing to their low-temperature processability, reduced hysteresis, flexible-substrate compatibility and suitability for perovskite/silicon tandem architectures. The buried interface is central to charge extraction, energy-level alignment, perovskite crystallization and operational stability, and is therefore a key determinant of device performance. Self-assembled monolayers (SAMs) are molecularly thin and offer negligible parasitic absorption, tunable interfacial energetics, low material loading and high structural designability, making them attractive alternatives to conventional organic Hole Transport Layers and effective hole-selective contacts in inverted PSCs. This review examines molecular design principles and interfacial engineering strategies for SAMs in inverted PSCs, focusing on the phosphonic acid carbazole (PACz) family, substituent and terminal-group engineering, and emerging conjugated backbones. We then summarize how SAMs regulate buried interfaces through energy-level alignment, defect passivation, crystallization control and stability enhancement. We further highlight emerging interface strategies, including co-assembled SAMs, amorphous SAMs, polymerized or crosslinked SAMs and molecular hybrid interfaces, and discuss how data-driven molecular screening may accelerate future SAM discovery. Finally, we discuss outstanding challenges in SAM formation, large-area uniformity, in situ and operando characterization, and data-driven molecular design, and provide perspectives on the use of SAMs in efficient, durable and scalable inverted PSCs.