This paper investigate the effectiveness of non-conjugated polymer polyvinylpyrrolidone (PVP) at the interface of an n-type metal oxide buffer layer and the photoactive layer in inverted bulk heterojunction solar cells. A 15% enhancement in power conversion efficiency (PCE) is realized after the incorporation of a thin PVP layer between zinc oxide (ZnO) and polythieno[3,4-b]-thiophene-co-benzodithiophene (PTB7):[6,6]-phenyl C₇₁-butyric acid methyl ester (PC₇₀BM) based photoactive layer in inverted polymer solar cells. The fabricated devices with the PVP layer show enhanced PCE as high as 7.30% under simulated AM 1.5 G (100 mW cm⁻²) illumination. The ZnO/PVP improves the electron extraction property of the ITO electrode, effectively blocks holes from the highest occupied molecular orbital of the donor, suppresses charge recombination at the interface of ZnO and the photoactive layer, and decreases the interfacial contact resistance.