Photocurrent characteristics of phthalocyanine/C60 p–n heterojunctions controlled by the work functions of metal electrodes

The photocurrent spectrum of Au/H2-phthalocyanine (H2Pc)/C60/metal heterojunction system, where metal=In, Cu, Au and Pt, was measured. When the metal electrode for C60 is the high work-function metal Pt, negative photocurrent, i.e. the photocurrent from C60 to H2Pc through the external load, is observed, while, with the low work-function metals In and Cu, positive photocurrent is observed. With the intermediate work-function metal Au, the sign of the photocurrent depends on the thickness of C60 film. Thus, the sign of the photocurrent has a clear correlation with the work function of the metal electrode. The negative photocurrent for the Pt and Au electrodes is explained by the competition of the p–n heterojunction of H2Pc/C60 with the Schottky junctions of C60/Pt (or Au) and Au/H2Pc.