Methodological problems of determining the mobility of excess charge carriers in molecularly doped polymers

The room-temperature mobility of holes in a molecularly doped polymer (polycarbonate containing 30 wt% of hydrazone) was studied by methods of nonstationary radiation-induced electric conductivity, time-of-flight measurements, and pulsed monopolar carrier injection. It was established that the hole transport in the polymer system studied during short periods of time (hundreds of microseconds or a few milliseconds) after the pulsed generation of carriers occurs in a dispersion regime (with a dispersion parameter of similar to 0.4). Then the effective mobility attains a plateau, and the transport regime changes from dispersion to Gaussian. The time-of-flight and stationary mobility values are strongly dependent on the strength of applied electric field. All three methods are virtually equally informative in studying the dispersion branch of the time variation of the effective mobility, while the Gaussian transport regime is more conveniently studied by the time-of-flight technique.