Models of Charge Generation and Transport

Charge transfer states (CT) are often found in molecular systems side by side with excitonic states. CT states describe polar nonconducting states bound by coulomb interaction of the electron-hole pairs. CT states may be ionized with localization of the charges on definite molecules. 

So the free charge carrier generation depends on the quantum yield of the creation of the thermalized pairs and the probability of their dissociation. 

Usually, one considers isotropic spatial distribution of the pairs and equal separation distance r for all pairs. Then 

The usual analysis of the experimental data consists of the measurement of the quantum efficiency versus electrical field and comparing the results with results theoretically calculated for different values of the parameters r0 e, T. 

The excited n-electron may tunnel through a potential barrier in the free state of the neighbouring molecule preserving the energy. The probability for tunnel transition is as a rule, more than the probability of the returning to the initial state. Apparently the energy of the potential barrier may be considered equal to the molecule ionization potential. The barrier form depends on the coulomb potential between the electron and positive ion and affinity of the neutral molecule. 

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A review is given on generation and transport of charge carriers in crystalline polydiacetylenes. Emphasis is placed on separating experimental facts related to both intrinsic photogeneration and time dependent transport from model considerations. The problem of crystal doping is briefly addressed. 

Possible Combination of Ion-Pumps and of the Active Glucose Transport Model (Combination of Pumps, Charge Generation and Selective Valve-Membranes)... 

In some polymers, the concentration of intrinsic, thermally generated, or photogenerated mobile carriers and their mobility are relatively high and these materials exhibit semiconducting properties. Because properties of polymeric semiconductors cannot be described by classical band theory elaborated for covalent crystalline semiconductors, some specific models used to describe charge carrier generation and transport in polymeric semiconductors will be presented in this section. 

We mentioned the main models for generation, transfer, and recombination of the charge carriers in polymers. Very often, these models are interwoven. For example, the photogeneration can be considered in the frame of the exciton model and transport in the frame of the hopping one. The concrete nature of the impurity centers, deep and shallow traps, intermediate neutral and charged states are specific for different types of polymers. We will try to take into account these perculiarities for different classes of the macro-molecules materials in the next sections. 

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