Heat treatment of amorphous silicon p-i-n solar cells with high-pressure H2O vapor

► Application of high-pressure H2O vapor heat treatment to a-Si:H solar cells. ► Increases in FF and efficiency by treatment at 210 °C at 2 × 105 Pa H2O for 1 h. ► A conversion efficiency increased from 7.7% to 8.4%. ► Carrier recombination sites were decreased by the H2O vapor heat treatment.