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The charge transport in a polyspirobifluorene derivative with copolymerized N,N,N′,N′-tetraaryldiamino biphenyl (TAD) hole transport units is investigated as a function of the TAD content. For TAD concentrations larger than 5%, guest-to-guest transport is observed. It is demonstrated that in this regime the charge carrier density dependent mobility can be described consistently with the extended Gaussian disorder model, with a density of hopping sites which is proportional to the TAD concentration and comparable to the molecular density.
Nicolai et al. (2011) studied this question.