Current conventional hole transport layers, such as poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine], are difficult to simultaneously possess the advantages of large-area fabrication, low-cost, and favorable perovskite crystallization. Therefore, the commercialization of perovskite solar cells (PSCs) is restricted. Here, [2-(9H-carbazol-9-yl)ethyl]phosphonic acid (2PACz), as a self-assembled material demonstrates its future potential as a commercial HTL. Due to its self-assembled properties and its strong polar carbazole group, 2PACz exhibits high thickness tolerance, excellent process flexibility, and good wettability to perovskite precursor. Thus, for the first time, a PSC with an efficiency of 20.75% and a V_OC as high as 1.185 eV is realized based on drop-coating 2PACz on ITO in the ambient environment. The reasons for the process flexibility and high thickness tolerance of 2PACz were systematically investigated by analyzing its molecular structure, aggregation state, film morphology, and the interaction characteristic between perovskite and 2PACz. Our research could pave the way for the commercialization of high-efficiency PSCs.