Electron-transfer process in layered photoreceptors containing azo compounds

Photoinduced electron transfer (ET) is the most essential process for carrier photogeneration in organic optoelectronic devices, In azo compound-based layered photoreceptors, carrier photogeneration is sensitized by hole transport material (HTM) incorporation. We investigated this process to elucidate the highly sensitizing mechanism. First, the photoinduced ET efficiency and overall quantum efficiency were measured and compared for the layered photoreceptor and the carrier generation layer. The result that the HTM enhances the photoinduced ET implies that the HTM works catalytically to diminish the activation energy. Although such extrinsic ET takes place independently of an electric field, the subsequent geminate pair dissociation depends on the electric field. Next, the energy-gap dependence of the ET was investigated by employing more than 50 photoreceptors to vary the energy gap over a wide range. The measured efficiency was plotted against the energy gap, in which an inverted region was not observed.