Exploring the temperature effect on hole transport properties in organic bulk heterojunctions.

The temperature effect on hole transport in representative organic bulk heterojunctions has been explored. Two model systems, namely, copper phthalocyanine (CuPc):fullerene (C), and zinc phthalocyanine (ZnPc):C, are chosen as case studies. The current-voltage (-) characteristics have been measured in hole-only configurations in the temperature range of 100-280 K and the temperature-dependent hole transport process has been revealed. At high voltages and temperatures from 180 to 280 K, charge transport is governed by the trapping model with space charge limited conduction in the presence of an exponential trap distribution. However, at temperatures below 180 K, the mobility model with field-dependent mobility fits the experimental data well, indicating that charge conduction occurs through a hopping mechanism. The extended state and localized state affected by temperature are responsible for hole transport in high and low temperature ranges, respectively.