Temperature-independent photoconductivity in thin films of semiconducting polymers: Photocarrier sweep-out prior to deep trapping

In thin films, the steady-state photoconductivity is temperature (T) independent in agreement with transient photoconductivity in the subnanosecond regime. As thickness is increased, an activated T dependence emerges. The T independence of the product of the carrier density (n) times the mobility (mu) for thin films results from carrier sweep-out prior to trapping; the crossover from T-independent mu to activated mu occurs when the transit time across the film is comparable to the time required for deep trapping. Thus, steady-state photoconductivity confirms that, in semiconducting polymers, the carrier generation mechanism is T independent, inconsistent with the Onsager model of photocarrier generation.