Versatile Self-Assembled Monolayer Enables High-Performance Inverted CsPbI3 Perovskite Solar Cells

Self-assembled monolayers (SAMs) have been widely employed as hole transport layers (HTLs) to construct efficient and stable organic-inorganic hybrid perovskite solar cells (PSCs). However, the related application of SAMs in inverted inorganic PSCs is still extremely limited. Herein, [2-(9H-carbazol-9-yl) ethyl] phosphonic acid (2PACz) is successfully developed as a nanoscale HTL to fabricate high-performance inorganic CsPbI3 PSCs. Compared with the conventional poly triphenyl-amine (PTAA), 2PACz SAM can tightly anchor on the fluorine-doped tin oxide (FTO) surface via chemical coordination, rendering a more favorable interface contact and matched energy level alignment with the perovskite. Besides, the perovskite film quality and interfacial charge extraction are greatly ameliorated, leading to suppressed charge recombination and voltage loss. As a result, the inverted CsPbI3 PSC with 2PACz HTL exhibits a champion power conversion efficiency (PCE) of 18.89% in contrast to the PTAA device with a lower PCE of 17.07%. Moreover, both the unencapsulated 2PACz-based perovskite film and device stability present significant improvement. This study provides insights into the underexplored application of SAMs in inorganic PSCs, which will accelerate the advancement of perovskite photovoltaics.