Photoconductivity enhancement of poly(3-hexylthiophene) by increasing inter- and intra-chain order

The transient conductivity of an organic thin film induced by the absorption of a nanosecond laser pulse can be probed by microwaves without the necessity of attaching electrodes to the sample. Poly(3-hexylthiophene), P3HT, samples of varying degrees of regioregularity and molecular weight were investigated. Films were produced by spin-coating or drop-casting in air or in a solvent-saturated atmosphere. We observed higher photoconductivity signals in films of higher regioregularity. Drop-casting as opposed to spin-coating yielded a further increase in the photoconductivity and also increased the lifetime of the mobile charge carriers. We conclude that the enhancement of the photoconductivity is due to a higher charge carrier mobility in films with increased intra- and inter-chain order in accordance with published results obtained from field-effect transistor studies.