Photocarrier generation

Recently, Itaya, Okamoto and Kusabayashi (14) made an estimation that the concentration of the electron-accepting photo-oxidation product of about 10 mol/mol monomer unit is necessary to interpret the high yield of the photocarrier generation of ca. 

From photoinduced absorption, luminescence and electron spin resonance observations, the dominant photocarriers generated in the polymer were shown to be polarons and bipolarons [189-191]. It was found that the magnitude of photoinduced absorption is rather independent of the condition of sample preparation whereas the photoluminescence intensity is strongly influenced. The results suggest that the luminescent exciton does not play a primary role in the photogeneration of polaronic species. 

Sensitivity is improved in GB-A-2094548. The length of the detector element or the magnitudes of the bias and scan velocity are selected so that the time taken to scan the detector element from one end to a read-out region is greater than the lifetime of the photocarriers generated in the element. 

Ikeda et a/.121 122 who studied sensitization of PVK by benzopyrylium and pyrylium salts provided evidence that the sensitization of the photocurrent in PVK and fluorescence quenching involve an electron transfer from PVK to an excited dye. The lower than expected quantum yield of photocarrier generation (<0.1)122 is explained by the need for the thermal dissociation of the photogenerated charge transfer complex into free holes and electrons. 

Figure 14 A model for photocarrier generation from the first excited singlet state.

Figure 10 The energy scheme of photocarrier generation of a dual-layer photoreceptor.

Kepler RG, Zeigler JM, Harrah LA, Kurtz SR (1987) Photocarrier generation and transport in s-bonded polysilanes. Phys Rev B 35(6) 2818-2822... 

Seiferfeld, Q., Ries, B. and Bassler, H., Field dependant photocarrier generation in crystalline polydiacetylenes,... 

Among a variety of titanyl phthalocyanines, the Y-form, developed by Konica, is said to be the most sensitive [12]. The quantum efficiency of the Y-form titanyl phthalocyanine for photocarrier generation is reported to be almost 1. The Y-form titanyl phthalocyanine is also reported to incorporate one water molecule to one titanyl phthalocyanine molecule in the crystal. The location of these water molecules in the crystal is as yet not dear, but they are considered to play an important role in the high sensitivity of the Y-form [13]. On the other hand, the incorporated water molecules are reversibly desorbed, and the sensitivity changes according to the quantity of water in the crystals. Because of such instabUity in sensitivity, photoreceptors with the Y-form of titanyl phthalocyanine have not yet been commercialized. 

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