Comparative study of hole transport in polyspirobifluorene polymers measured by the charge-generation layer time-of-flight technique

Hole transport in a polyspirobifluorene homopolymer and a statistical polyspirobifluorene-triarylamine copolymer has been studied in detail employing the charge-generation layer time-of-flight (TOF) technique over a wide range of electric fields and temperatures. Both materials exhibit nondispersive TOF signals after injection of a sheet of charge carriers from a thin $\left(10\mathrm{nm}\right)$ perylene-diimide charge-carrier generation layer into a relatively thick $(d>1\mathrm{\mu }\mathrm{m})$ polymer film. Results were analyzed within the framework of the Gaussian disorder model and the charge transport parameters were extracted for both polymers. The zero-field hole mobility of the spirohomopolymer was found to be on the order of ${10}^{-6}{\mathrm{cm}}^2∕\mathrm{V}\mathrm{s}$ , whereas the copolymer showed a considerably lower hole mobility of $6\times {10}^{-8}{\mathrm{cm}}^2∕\mathrm{V}\mathrm{s}$ . The width of the density of states $\sigma$ was determined to be $86\mathrm{meV}$ for the homopolymer and $107\mathrm{meV}$ for the copolymer. The latter polymer also showed an increased positional disorder due to the statistically incorporated triarylamine units.