Enhanced Ultraviolet Emission in Polysilane Light-Emitting Diodes by Inserting a SiOx Thin Layer

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Abstract
Bilayered polysilane light-emitting diodes (LEDs) have been fabricated by inserting a SiO x thin layer between the cathode and a poly(methylphenylsilane) (PMPS) film employed as an emission material. The SiO x layers were prepared by O2 plasma treatment of the PMPS film surfaces. It was found that the external quantum efficiency was significantly enhanced by this treatment. The enhancement may be caused by the increased electron injection due to the tunneling effect and the reduced hole current due to the blocking effect by the thin SiO x layer. Experiments also showed that the weak visible emission invariably observed from single-layer polysilane LEDs was almost completely eliminated. It is concluded that the visible emission is caused by the erosion of the PMPS surfaces occurring due to the collision with hot metal particles during the vacuum deposition of the cathode, and this erosion is avoided by the SiO x layer.