Charge transport percolation models

Charge transport in the accumulation channel is described by the percolation model [24] based on thermally activated tunneling of holes between localized states in an exponential density of states, described in Section 13.2.2. In the accumulation regime this Variable Range Hopping (VRH) model yields a gate-voltage dependent field-effect mobility of the form ... 

A different explanation was proposed by Hsu et al. Dedoping of PEDOT was ruled out as the total number of injected ions from out of the gate into the PEDOTPSS channel was too low to explain the observed current decrease. Instead a model was favored assuming a change of percolation paths caused by rendered ion positions. A small fraction removal of mediated hopping states near the Fermi level on charge transport paths causes carriers to hop over longer distance to conduct current and therefore fp is reduced. 

The high aspect ratio of nanorods can facilitate charge transport, while the handgap can he tuned by vaiying the nanorod radius. This enables the absorption spectmm of the devices to be tailored to overlap with the solar emission spectmm, whereas traditionally polymer absorption has been limited to only a small fraction of the incident solar irradiation. At present, the nanorods in polymer solar cells are typically incorporated into a homopolymer matrix. An alternative to this approach is to incorporate the nanorods into either a polymer blend or diblock copolymer system. The photovoltaic properties of nanorod polymer composites could potentially be improved due to the percolation of nanorods, and the presence of continual electrical pathways, from the DA interfaces to the electrodes. To test this hypothesis, we use the distribution of nanorods from the self-assembled stmcture in Figure 1(b) as the input into a drift-diffusion model of polymer photovoltaics. 

The common disadvantage of both the free volume and configuration entropy models is their quasi-thermodynamic approach. The ion transport is better described on a microscopic level in terms of ion size, charge, and interactions with other ions and the host matrix. This makes a basis of the percolation theory, which describes formally the ion conductor as a random mixture of conductive islands (concentration c) interconnected by an essentially non-conductive matrix. (The mentioned formalism is applicable not only for ion conductors, but also for any insulator/conductor mixtures.)... 

Systems involving granular metal particles and polymers have been modeled in terms of mixtures of random voids and conductive particles. There is also an inverted random void model [15]. For CB in polymers, percolation is the process by which charge is transported through a system of interpenetrating phases. 

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