Temperature dependence of photoconductivity in buckminsterfullerene films

We report the temperature dependence from 330 to 230 K of the photoconductivity measured in sublimed films of buckminsterfullerene, specifically, C60/70, up to 3 μm thick. In contrast to the temperature dependence of the dark conductivity, where reversible structure, associated with the onset of a phase transition to orientational ordering below 250 K, is observed, the photoconductivity shows an essentially monotonic decrease to lower temperatures. This provides additional evidence that the thermal generation rate increases as the C60/70 becomes orientationally ordered. It also suggests that the increased order below the transition temperature does not lead to significantly increased carrier mobilities.