Electronic energy states of organic interfaces studied by low-energy ultraviolet photoemission spectroscopy

Ionization potentials of conducting polymer/metal interfaces and conducting polymer/poly(p-pyridyl vinylene), PPyV, interfaces were evaluated by a low-energy photoelectron spectroscopic method, and interfacial electronic states were determined. At all the measured interfaces, a shift of the vacuum level was observed, and was attributed to the formation of an interfacial electric dipolar layer. The shifts of the ionization potential at the interface could be expressed as a linear function of the work function of the contact metal. However, for conducting polymers/indium-tin-oxide interfaces, interfacial electronic states could not be determined. This may be related to the novel ionization potential behavior in those systems. The present results clearly demonstrate that characterization of the interfacial electronic states is necessary for a complete understanding of the characteristics of organic electronic devices. (C) 1999 American Institute of Physics. [S0021-8979(99)00916-0].