Cesium doping at C{sub 60}/rubrene heterointerfaces for improving the performance of organic light- and current-generating devices
This study examined the effect of adding cesium (Cs) at C{sub 60}/rubrene heterointerfaces by using synchrotron-radiation photoelectron spectroscopy. A C{sub 60}/rubrene heterostructure is the basis of a novel organic dual device found to facilitate efficient integration of both electroluminescent and photovoltaic functions. With Cs doping, the interfacial dipole potential was considerably enlarged, as was the separation between the lowest unoccupied molecular orbital of C{sub 60} and the highest occupied molecular orbital of rubrene. However, the energy-level diagram indicated that a high Cs concentration prevents the formation of photoexcitons. By contrast, adding a small amount of Cs can effectively improve the efficiency of light- and current-generating devices. In particular, the deficiency of the dopants at the heterointerface may benefit the survival of photoexcitons.