Percolative aspects in photoconductivity

We present transient photocurrent measurements on samples containing a benztriazole derivative embedded in polycarbonate matrices and we obtain the effective carrier mobilities and their dependence on concentration. This dependence can be viewed in terms of a critical concentration $p_c$ and a critical exponent $\overline{t}$. Our values of $p_c=0.1\mathrm{}$ and $\overline{t}=2.5\mathrm{}$ are similar to recent findings on continuum percolation. In contrast to simple percolation, the mobility is also field and temperature dependent, obeying a Poole-Frenkel behavior.