Applications, photoconductors processibility

Polymers with saturated bonds, heteroatoms, heterostructures and poly-conjugated ones are available now as photosensitive materials. Really one cannot expect a single mechanism to be reponsible for photoconductivity in so many diverse systems. However, there are a lot of verified factors which permit us to explain the main features of the photoconductive processes in polymers. The status and prospects of the application of polymeric photoconductors as prospective new electronic materials will be also analyzed for various types of photoconductors. 

Nowadays, polymeric photoconductors may be used in electrophotography, microfilms, photothermoplastic recording, spatial light modulators, and nonlinear elements. The combination of photosensitivity with high quality electrical and mechanical properties permits the use of such materials in optoelectronics, holography, laser recording and information processes. The applications of the various types of polymers were reported in the final parts of the relevant items in the earlier sections. Here, we will briefly analyze the common features of photoconductive polymer applications. The separate questions of each type have been dealt with in some books and papers [3, 11, 14, 329]. 

Deep centres are often present in photoconductors and they can trap the photo-generated carriers. The statistical trapping (recombination or capture) and subsequent release (generation or emission) of these carriers leads to an extra source of noise called generation-recombination (g-r) noise. The presence of this noise depends on the purity of the material used as a photoconductor, but in some cases, it is inherent to the deliberate technological process as recombination centres can be added to reduce the time constant of the detector for specific applications. The time constant r of a single trap is related to its capture and emission time constants rc and re by r 1 = r 1 + t"1, and when the g-r noise arises from a trap with a definite value of r, the observed noise spectrum has a Lorentzian dependence on the modulation frequency /, peaking at /o = l/2nr. 

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