Effect of K doping on CuPc: C60 heterojunctions

Abstract

Here, the electronic properties of K-doped copper phthalocyanine (CuPc): C60 heterojunctions are studied via synchrotron-radiation photoemission. The K-doped heterointerfaces were obtained by means of C60 on K1.5CuPc and CuPc on K3C60. The photoelectron spectra show that the potassium prefers to combine with C60. At the C60/K1.5CuPc interface, the K diffuses and transfers negative charge into the C60 overlayer, while no strong chemical reaction could be found at the CuPc/K3C60 interface. A significant shift of the vacuum level was observed in both cases, which was caused by the charge transfer for the C60/K1.5CuPc and by the induced density of interface states (IDIS) dipole for the CuPc/K3C60. The energy level diagrams show that using C60 adsorption on a K-doped CuPc film is good for the improvement of photovoltaic devices. However, the inverse process, that of CuPc on a K-doped C60, is unfavorable for the photovoltaic effect.