INTERFACIAL PROPERTIES OF THE K-DOPED C60: CUPC HETEROJUNCTIONS

We report on the interfacial properties of the K-doped C-60: copper phthalocyanine (CuPc) heterojunctions, studied via synchrotron-radiation photoemission. The K-doped heterointerfaces were obtained by means of C-60 on K1.5CuPc and CuPc on K3C60. The valence-band and K 3p core-level spectra show that the K diffuses and transfers negative charge into C-60 overlayer at the C-60/K1.5CuPc interface, while only physisorption could be found at the CuPc/K3C60 interface. A significant shift of the vacuum level is observed in both cases, caused by the charge transfer for the C60/K1.5CuPc, while by the pillow effect for the CuPc/K3C60. The creation of gap states and an increased separation between the lowest unoccupied molecular orbital of C-60 and the highest occupied molecular orbital of CuPc at the C-60/K1.5CuPc interface reveal that the K-doped film could improve the photovoltaic effect. However, the advantage has not been found at the CuPc/K3C60 interface.