As interest in pin perovskite solar cells (PeSCs) capable of low temperature solution process increases, research on the low temperature solution processable hole transport layer (HTL) is emerging as an important issue. Although a solution processed nickel oxide (NiO) has been spotlighted as an optimal HTL, high temperature post treatment over 250 ℃ is required for suff cient device performance. In this study, NiO film fabricated from presynthesized NiO nanoparticle dispersion is investigated as HTLs and their interface is modified with [4-(3,6 dimethyl-9H carbazol 9 yl)butyl]phosphonic acid (Me 4PACz) to demonstrate highly efficient PeSCs processed at ~100 ℃. The combination of the low temperature processed NiO with optimal thickness (~10 nm) and Me 4PACz exhibits higher efficiency of 17.4% comparing to bare NiO based device showing 12.4%. Me 4PACz modification on NiO results in an improved energy level alignment with perovskite and more hydrophobic NiO/Me 4PACz induces excellent perovskite layer with larger grain and high crystallinity. Furthermore, the NiO/Me-4PACz-based PeSC maintains 83% of their initial efficiency after 140 days in air. This result shows that our low temperature solution processed NiO/Me 4PACz can be a promising candidate as HTLs even in terms of stability.