Cesium doping at C₆₀/rubrene heterointerfaces for improving the performance of organic light- and current-generating devices

This study examined the effect of adding cesium (Cs) at C₆₀/rubrene heterointerfaces by using synchrotron-radiation photoelectron spectroscopy. A C₆₀/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 C₆₀ 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