A nanocomposite of highly conductive C-60 and insulating LiF (C-60:LiF) is shown to function as both a highly effective passivation layer and hole blocking layer in polymer bulk heterojunction solar cells. C-60:LiF composites with up to approximate to 80% LiF concentration dramatically increase the device stability and power conversion efficiency, enabling a new generation of high-performance and long lifetime organic photovoltaics on flexible substrates.