Extrinsic Photogenerators

Figure 16. Schematic energy diagram for intrinsic photogeneration in an azo pigment and extrinsic photogeneration in the presence of a donor hole transport molecule. (Reprinted with permission from Ref. [34b].)...

Figure 10.26. Definitions of the intrinsic and extrinsic photogeneration processes.

An injection of carriers only occurs if an extrinsic photogenerator is used together with a charge transporting material. Usually dye particles are dispersed in a... 

M. Yokoyama, Y. Endo, A. Matsubara, and H. Mikawa. Mechanism of extrinsic carrier photogeneration in poly-n-vinylcarba-zole. ii. quenching of exciplex fluorescence by electric field. J. Chem. Phys.,... 

The phthalocyanines are still of some interest, and Ayers has interpreted the photoelectrochemistry of copper phthalocyanine in terms of the band-model for semiconductors. Menzel et alf have studied the photoconductivity and electrical field-induced fluorescence quenching in metal-free phthalocyanine films. Doping of the film increases charge-carrier photogeneration, and it seems likely that the mechanism is extrinsic, involving field-assisted exciplex dissociation. These are complicated materials, which are difficult to purify, and the mechanisms of carrier generation in polycrystalline and amorphous films are still obscure. The porphyrins and monolayer assemblies of chlorophyll on SnOj electrodes 2 72,273 ijggjj studied. 

Fig. 6.8a and b. The use of CCD registers for TDI. (a) IR active CCD register (monolithic focal plane array with photogeneration in the register), (b) Direct injection with Si parcel in series out CCD register hybrid with IR photodiodes or monolithic with silicon IR extrinsic photoconductors... 

A variety of azo and methine dyes and pigments have been examined in conjunction with PVK and other polymers, but the patent literature indicates that virtually any dye or pigment can sensitize the photoconductivity of PVK into the visible range. When photogeneration proceeds via electronic transitions involving both the polymer and the dye (such as a charge-transfer complex between PVK and the acceptor part of the dye), the process is also considered intrinsic. When these transitions proceed within the dye molecules or pigment particles, the process is termed extrinsic. 

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