Fundamentals of Charge Transport Mechanism

Organic Electronics Materials, Processing, Devices and Applications 

Hopping transport mechanism— if the lattice is irregular, or if the carrier becomes localized on a defect site, then lattice vibrations are essential if the carrier is to move from one site to another. This is an activated process and the mobility increases with increasing temperature. 

The second approach deals with charge transport macroscopically. An amorphous organic semiconductor can be treated as an ensemble of disordered hopping sites through which injected carriers drift xmder the influence of an external applied field. Historically, the Poole-Frenkel (PF) model was one of the first models to explain the electric field dependence of charge carrier drift mobilities [21,22], The field-dependent mobility can be written as 

Po is the zero-field mobility F is the electric field cj is the unit of electronic charge e is the dielectric constant Ppp is the PF slope 

It may be obtained experimentally from a plot of log p vs at a constant temperature. In many organic disordered systems, the hole and electron mobilities were reported and clearly follow the PF relation shown in Equation 3.4 [23-26]. The PF model, however, has a serious deficiency. According to Equation 3.5, it makes a definitive prediction on the value of Ppp. Yet, it turns out that most experimental results deviate significantly from the theoretical value of Ppp. 

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After a brief discussion of fundamentals of charge transport mechanisms, this chapter summarizes and discusses the most significant results obtained by using different junctions and in particular LAJs. In order to facilitate a systematic discussion, we make a functional distinction between non-active and active junctions we will refer to active junctions as those aimed at changing the electrical response by means of an external stimulus acting in situ to modify the molecular electronic structure non-active junctions are those used to measure and compare the electrical properties inherent to the different electronic structure of incorporated molecules, without any modification induced by an external signal. 

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