In this paper we demonstrate an efficient inverted polymer bulk heterojunction (BHJ) solar cells using solution processed interfacial layer by mixing zinc oxide (ZnO) with cesium carbonate (Cs2CO3) for ideal electron extraction and transport. The optimized inverted BHJ solar cell with n-type mixed (ZnO:Cs2CO3) electron transport layer and blend of poly (3-hexylthiophene):Indene-C60 bisadduct as a photoactive layer shows a power conversion efficiency as high as 5.29%. This performance enhancement is attributed to improved interfacial contact between photoactive layer and electron extraction layer, low leakage current, and a suitable surface morphology for electron extraction and transport. (C) 2014 Elsevier B.V. All rights reserved.