Hole mobilities in films of a pyrazoline:polycarbonate molecularly doped polymer.

The hole mobilities \ensuremath{\mu} of solution cast 1-phenyl-3-p-diethylaminostyryl-5-p-diethylphenyl-pyrazoline:polycarbonate (DEASP:PC) thin films have been characterized by the time-of-flight technique. The mobilities were measured for DEASP doping concentrations in the range 10\char21{}90 % over a wide range of temperatures and electric fields, including measurements above the glass transition temperature ${\mathit{T}}_{\mathit{g}}$, and analyzed with use of recently suggested deconvolution procedures. The independence of the activation energy on the calculated distance between DEASP molecules \ensuremath{\rho} and the exponential dependence of \ensuremath{\mu} on \ensuremath{\rho} suggest nonadiabatic small-polaron hopping is occurring, as was concluded for the molecularly doped polymer hydrazone:PC. The decrease in activation energy above the glass transition temperature is clear evidence of the role of the polymer matrix in determining the activation energy. The electric-field dependence of \ensuremath{\mu}, while similar to previous measurements, i.e., ln\ensuremath{\mu}\ensuremath{\propto} \ensuremath{\surd}E , provides significant new information. We report the first characterization of the field dependence of \ensuremath{\mu} above the glass transition temperature: It appears to be unaffected by ${\mathit{T}}_{\mathit{g}}$, in contrast to the behavior of the activation energy. We also report the first observation of a mobility that decreases as the electric field increases at 10% DEASP concentration above 370 K. This result is contrary to the predictions of several investigators, but consistent with empirical equations suggested earlier.