Effects of NPB anode buffer layer on charge collection in ZnO/MEH-PPV hybrid solar cells

We investigate the effects of (N,N’-diphenyl)-N,N’-bis(1-naphthyl)-1,1’-biphenyl-4,4’-diamine (NPB) buffer layers on charge collection in inverted ZnO/MEH-PPV hybrid devices. The insertion of a 3-nm NPB thin layer enhances the efficiency of charge collection by improving charge transport and reducing the interface energy barrier, resulting in better device performances. S-shaped light J–V curve appears when the thickness of the NPB layer reaches 25 nm, which is induced by the inefficient charge extraction from MEH-PPV to Ag. Capacitance–voltage measurements are performed to further investigate the influence of the NPB layer on charge collection from both simulations and experiments.