Photoelectron spectroscopy study of the energy level alignment at polymer/electrode interfaces in light emitting devices

The band alignment at the interface between electroluminescent polymers and the electrodes in polymer-LEDs was studied using photoelectron spectroscopy. Chemical factors like the formation of InCl3 during conversion of precursor-PPV on ITO could be directly monitored with XPS. Films of electroluminescent polymers were studied on a range of ITO and metal electrodes with different work functions, as well as with an intermediate, electrically conducting polymer layer, using UPS. Furthermore, the study of the band alignment at polymer electrode interfaces was extended to three-layer structures: the results confirm the common assumption that the potential drop over the polymer layer in polymer LEDs is equal to the difference between the electrode work functions.