Carrier photogeneration and mobility in polydiacetylene: Fast transient photoconductivity

Transient photoconductivity experiments have been carried out on single crystals of polydiacetylene-(bis p-toluene sulfonate), PDA-TS. The low-electric-field photocurrent decay consists of a temperature-independent fast (picosecond) initial component and a longer-time (nanosecond) component with magnitude that is strongly temperature dependent. Using very small spacings between electrodes on the sample, we have succeeded in achieving sweepout for the longer-lived carriers; the data yield a mobility of ~=5 cm²/V.s at room temperature in the nanosecond regime. These results demonstrate that the Onsager geminate recombination model, previously used extensively for the polydiacetylenes, is not applicable to PDA-TS.