The advancement of perovskite solar cells (PVSCs) technology toward commercialized promotion needs high efficiency and optimum stability. By introducing a small molecular material such as tetratetracontane (TTC, CH3(CH2)42CH3) at the fullerene (C60)/perovskite interface of planar p-i-n PVSCs, we significantly reduced the interfacial traps, thereby suppressing electron recombination and facilitating electron extraction. Consequently, an improved efficiency of 20.05％ was achieved with a high fill factor of 79.4％, which is one of the best performances for small molecular-modified PVSCs. Moreover, the hydrophobic TTC successfully protects the perovskite film from water damage. As a result, we realized a better long-term stability that maintains 87％ of the initial efficiency after continuous exposure for 200 h in air.