The charge trapping rate distribution in polycrystalline films of thionaphthenindole is inferred from transient photocurrent measurements and a multiple trapping model of dispersive transport. The distribution is found to have a high value “flat” part suggesting that the charge transport is governed by homogeneously distributed traps in the range 0.35–0.41 eV. Propagation of a carrier packet in an external electric field is modified to include its diffusion enhanced by the trap-induced charge carrier density gradient during a single transit. The electric field decrease in the measured carrier mobility can be explained by reinterpreting transit time data including the carrier diffusion. Both the mobility data and the trapping characteristics are compatible with the results for the photoelectric quantum yield measured under steady state and transient current conditions.