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 (10nm) perylene-diimide charge-carrier generation layer into a relatively thick (d>1μm) 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 10−6cm2∕Vs, whereas the copolymer showed a considerably lower hole mobility of 6×10−8cm2∕Vs. The width of the density of states σ was determined to be 86meV for the homopolymer and 107meV for the copolymer. The latter polymer also showed an increased positional disorder due to the statistically incorporated triarylamine units.