Electron Injection Process in Light-Emitting Diodes Made from Polysilanes as Manifested by Incorporation of Electron Injection Layers

The electron injection process was investigated for poly(methylphenylsilane) (PMPS) in two-layer light-emitting diodes (TL-LEDs) composed of a PMPS film and a vacuum-deposited film of oxadiazole molecules (OXDs). The latter acts as an electron injection layer. The basic characteristics of the TL-LEDs were markedly better than those of single-layer LEDs. The magnitude of the accompanying red-shift in the EL spectrum coincides with the energy difference between the conduction band and/or the one-dimensional exciton level of PMPS, and the conduction band of an OXD layer. This study has revealed that electron injection in PMPS is an energy selective process occurring via surface defect levels which exist below the conduction band of the OXD layer in terms of energy, and that the electron-hole recombination takes place in the PMPS layer near the interface with the OXD layer.