In the study, we inserted different types of intrinsic and p-type layers as the p/i buffer layer in hydrogenated amorphous silicon (a-Si:H) solar cells and investigated their effects on device performance. The band gap and activation energy of the buffer layer had a significant effect on the open-circuit voltage (V-oc) of the cells. Inserting a hydrogenated intrinsic amorphous silicon oxide (i-a-SiOx:H) layer as the p/i buffer layer in a-Si:H solar cells leads to a significant V-oc increase up to 909 mV. It also increased the external quantum efficiency at 400 nm to 75%. This was primarily owing to the increase in the built-in electric field and a decrease in the rate of carrier recombination at the p/i interface. Finally, the initial conversion efficiencies of single-junction a-Si:H solar cell and hydrogenated amorphous silicon/hydrogenated microcrystalline silicon (a-Si:H/mu c-Si:H) tandem solar cell could be increased to 10.64% and 12.24%, respectively. (C) 2014 Elsevier B.V. All rights reserved.