Photoelectron spectroscopy study of the electronic structures of poly(p-phenylenevinylene) derivatives

Using X-ray and ultraviolet photoelectron spectroscopy (XPS & UPS)I we have investigated the electronic structures of poly(p-phenylenevinylene) (PPV) derivatives with different side chains. The results of the XPS peak-shape a nalyses for the C-C, the C-O, and the C-N bonds were consistent with the va lues deduced from the chemical formula and the tabulated peak-position shif ts. The locations of the energy levels relevant to organic light-emitting d evice (OLED) applications of these materials were obtained from UPS spectra and were compared with the results of the OLED performance parameters. The values of ionization potential correlated well with the field strengths fo r the onset of luminescence. However, the efficiency of the devices did not follow the trends of electron affinity. The implications of these results, as well as other factors governing the efficiencies of OLEDs, are discusse d.