Modifications of the ZnO electron extraction layer with a mild hydrogen plasma treatment increased the efficiency of inverted polymer solar cells (PSCs) based on three different photoactive blends, namely poly(3-hexylthiophene):[6,6]-phenyl C71 butyric acid methyl ester (P3HT:PC71BM), P3HT:1′,1′′,4′,4′′-tetrahydro-di[1,4]methanonaphthaleno-[5,6]ullerene-C60 (P3HT:IC60BA) and poly[(9-(1-octylnonyl)-9H-carbazole-2,7-diyl)-2,5-thiophenediyl-2,1,3-benzothiadiazole-4,7-diyl-2,5-thiophenediyl] (PCDTBT:PC71BM), irrespective of the donor:acceptor combination in the photoactive blend. The drastic improvement in device efficiency is dominantly attributable to the reduction in the work function of ZnO followed by a decreased energy barrier for electron extraction from fullerene acceptor, and consequently, reduced charge recombination. In addition, improved nanomorphology of the photoactive blend when deposited on top of the H plasma treated ZnO layer was observed while exciton dissociation also strongly improved with hydrogen treatment. As a result, the inverted PSC consisting of the P3HT:PC71BM blend exhibited a high power conversion efficiency (PCE) of 4.3%, the one consisting of the P3HT:IC60BA blend exhibited a PCE of 6.6% whereas our champion device consisting of the PCDTBT:PC71BM blend reached a PCE of 7.4%.