Effect of K Doping on Rubrene: C60 Heterojunctions

Using synchrotron-radiation photoemission spectroscopy, we have studied the effect of K doping on rubrene: C60 heterojunctions. The K-doped heterointerfaces was obtained by means of C60 on a K-rubrene surface. As the heterointerface formed, the K diffuses into the C60 overlayer, and transfers negative charge into the lowest unoccupied molecular orbital (LUMO) of C60, resulting in a significant interfacial dipole potential. With K doping, the creation of gap states, providing complementary absorption channels, may expand photon harvesting. Furthermore, the increase in the separation between the highest occupied molecular orbital (HOMO) of rubrene and the LUMO of C60 could possibly be applied to increase the open circuit voltage of organic photovoltaic devices.