Transport states, Gaussian density

Figure 5. The amorphous structure of an organic matrix leads to a Gaussian density of states for the HOMO of the donor transport matrix. Some of the donors will have a relatively small oxidation potential (in the shaded region) and these sites are likely to experience a potential barrier inhibiting charge hopping to adjacent sites of higher oxidation potential. A hole may in this way become an immobilized cation.

Jansson F, Baranovskii SD, Gebhard F, Osterfoacka R (2008) Effective temperature for hopping transport in a Gaussian density of states. Phys Rev B 77 195211... 

Vs//2. The energetic disorder o can be imderstood as the width of the Gaussian distribution of the density of energy states for the transport sites the positional disorder E can be treated as the geometric randomness arising from structural or chemical defects [28,29]. In essence, only two material parameters, viz., a and E, are used to describe the randomness of the amorphous organic charge transporter. The PF slope, Ppp, is now replaced with P in Equation 3.7, and in the context of the GDM, it is related to the disorders of tire material. From Equations 3.6 and 3.7, o can be determined from the slope of the plot of p(0,T) vs l/T, while E can be determined from the x-intercept of a plot of P vs (cs/k Tf. 

An alternative approach [28, 50-54] is based on the assumption that the density of states can be modelled by a Gaussian distribution. Charge carrier transport occurs via direct hopping between the localized sites. In general, the differences between the two models are too small to be detected experimentally. Since our data can be quantitatively explained within the framework of multiple trapping we will restrict the discussion to this model. 

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