The excellent electron transport properties of a ZnO interfacial layer in conventional perovskite solar cells (PSCs) lead to high power conversion efficiency (PCE). The perovskite layers are generally affected by decomposition via the interfacial layers of ZnO. In this work, we address the decomposition issue by modifying the ZnO surface with a uniformly assembled thin layer of poly-vinylpyrrolidone (PVP) or p-aminobenzoic acid (PABA), creating an interfacial modification layer. The PVP- or PABA-modified ZnO surface provides better wettability and adhesion during the deposition of the perovskite active layer structure above it, making the perovskite morphology more uniform and pinhole-free. PSCs with PVP- and PABA-modified ZnO substrates achieve PCE values of 14.12% and 14.07%, respectively. The modified ZnO surface also has high thermal stability (60 min at 90 degrees C).