In Situ Crosslinked Phosphonic Acid Self‐Assembled Monolayers Toward Efficient and Stable Inverted Perovskite Solar Cells

Abstract Hole‐selective self‐assembled monolayers (SAMs) have emerged as a novel recombination junction material critical in the development of high‐performance photovoltaic devices. However, SAMs tend to accumulate on substrates and can be desorbed by the strong polar solvents, resulting in poor‐quality perovskite films. Herein, a simple phosphonic acid SAM molecule named V3PACz with vinyl ether side groups is first and strategically developed for in situ fabrication of polymeric hole‐transport layer (HTL). The side chain of vinyl improves the surface polarity and solubility of SAM. More importantly, the vinyl groups enable in situ polymerization, forming a densely packed and stable HTL with high conductivity and high anti‐solvent resistance. Meanwhile, Poly‐V3PACz synchronously provides satisfied surface wettability and interfacial functionalization. Utilizing these advantages, Poly‐V3PACz‐based device achieves champion power conversion efficiency of 25.21%, which represents the one of the highest reported efficiencies for in situ crosslinked HTLs and polymeric SAMs in inverted PSCs. The unencapsulated device maintained 92.1% of its initial PCE after 500 h storage at 85 °C (dark), and 91.9% initial PCE after 1200 h tracking at the maximum power point (MPP). This work underscores the promising potential of in situ crosslinking strategy in fabricating polymeric SAMs toward Efficient and Stable PSCs.