Variable range-hopping model

We note a temperature dependence of the zero field mobility as exp[—( F()/F)2], a behavior which is indeed encountered in real organic semiconductors, and differs from both Millers-Abrahams fixed range and Moll s variable range hopping models. 

Until the fabrication of the first conductive LB film by Ruaudel-Teixier et al. [20], LB films had been considered as insulators or at most as semiconductors with very low conductivities. This is understandable since the typical film-forming molecules are long-chain fatty acids, which can act only as insulators. It is no wonder that the first systematic investigations of the electrical properties of LB films were carried out for insulating LB films [21-30]. Mott s variable-range-hopping model [31] is employed to explain the results [21,24]. 

Table 12.4. Parameters obtained from the least-squares fitting of the Mott variable range hopping model to the data shown in Figure 12.4 (see text for parameter definitions and film designations)...

Epstein et al. [41, 54, 71] suggested that the sulfonated polyanilines have much stronger temperature dependence conductivity than emeraldine hydrochloride due to greater electron localization. The temperature dependence of the conductivity of 50 % [41], 75 % [54] and fully ring sulfonated polyanilines [71] was best fit by the quasi one-dimensional variable range hopping model described by Equation (2.1) ... 

We do not enter into the details of the many models proposed to explain the conduction properties in conjugated materials. These include, for instance, the variable range-hopping model (VRHM), descriptions based on electronic tunneUng effects and on the granular metallic model and other variants, whose features are widely available in the literature. We only mention a couple of examples. In the simplest case, as an effect of disorder, the mobility can follow an Arrhenius law, namely a thermally activated dependence on temperature ... 

Fig. 19 Variable range hopping model for moderately doped polyacetylene (Ref. 9)...

PEDOT PSS can be described as a heterogeneously disordered conjugated polymer. The large disorder in PEDOT PSS is a major difference to other conductive polymers such as polyacetylene or polypyrrole. The temperature dependence of conductivity in PEDOT PSS films is discussed in Chapter 9 with a particular focus on the results obtained using the variable range hopping model. There are different conclusions about the dimensionality of the hopping mode.i The electronic states in PEDOT are also discussed in Chapter 9... 

Temperature Dependence of PEDOT PSS Films, Discussed in Terms of the Variable Range Hopping Model... 

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