Photoconductive polymer

Photoconductive polymers absorb electromagnetic radiation and produce an increase of electrical conductivity.

Photoconductive polymers have been used in a wide variety of technical applications such as Xerography (electrophotography) and laser printing.

Photoconductive polymers can serve as good insulators when the electricity, free electrons and holes are absent.

The photoexcited electron will form a pair of charge carriers, it can be separated by electric field.

One prominent example is hydrogenated amorphous silicon in which a metastable reduction in photoconductivity is observable.

[2] Other materials that were reported to exhibit negative photoconductivity include molybdenum disulfide,[3] graphene,[4] and metal nanoparticles.

The charge-carrier generation can be affected in different aspects: photons absorbed, polymer itself, photoexcitation of photosensitive material.

[7] As Onsager originally developed this theory:[8] The encounter complex will be formed by photoexcitation with migration of the exciton to an acceptor site.

The photogeneration efficiency is determined by the competition between carrier separation and geminate recombination.

The photogeneration efficiency was defined by using the dissociation of ion pairs in weak electrolytes, which can be expressed as a function of electric field, temperature and the separation distance of the bound hole-electron pair.

is the rate of the density of free carriers in the generation layer reduced by recombination,

In this process, electrons or holes or both, involves 'hopping', for example, a sequence of transfers of charges among localized sites.

[11] These localized sites are connected with individual functional groups or segments of the polymer chain.

(2)Photoconductive polymers have an extended π-electron system in the backbone pendant to the chain.

In this process, charged moiety can be illustrated by the scheme:(a) The redox steps to achieve trap-free migration of a hole involving neutral groups M and charged groups M+ (b) The intermittent species Mj+ can undergo two kinds of process: (i) The migration of electron from Mk will result in forming Mj coming from Mj+ (ii) Mj+ undergo a side-reaction leading to a charged species X+ that won't further exchange the charge with the neighboring group M.[13] There are some parameters in photoconductive polymers: quantum efficiency of photogeneration

The charges will be generated in the region, which closed to the electrode the incident photos are absorbed.

In order to avoid the migrating charges as a current pulse, RC have a smaller value than

In the xerographic technique, the corona-deposited charge plays the same role as the semitransparent electrode.

The charge-transport layer is a solid solution compared with other printer that usually use liquid chemicals in printing process.

The main advantages of organic photoconductive polymer are (i) near-IR sensitivity (ii) panchromaticity (iii)flexibility for application (iv) simple fabrication (v) low cost.

Currently, the best organic photoconductive polymer are as sensitive as the inorganic devices based on selenium.

The limit of this application is that photoconductive polymer don't have high conversion efficiency.

Its fundamental principle was invented by Chester Carlson in 1938 and developed and commercialized by the Xerox Corporation, which is used for high-quality printing.

In traditional reproduction techniques, liquid chemicals are involved in printing process.

Xerography use photoconductive polymer as the foundation material, which is solid chemicals.

It was almost 18 years before a fully automated process was developed, the key breakthrough being use of a cylindrical drum coated with selenium instead of a flat plate.

[26] The drum can selectively collect electrically charged powdered ink (toner), and transfers the image to paper.

As digital photocopiers, laser printers employ a xerographic printing process.

Laser printers were introduced for the office and then home markets in subsequent years by IBM, Canon, Xerox, Apple, Hewlett-Packard and others.

[28] Over the decades, quality and speed have increased as the price fall, and the once cutting-edge printing devices are now ubiquitous.