Dual photoluminescence of polythiophene thin films

Transient photoluminescence of electrochemically prepared thin films of polybithiophene and polyterthiophene was analyzed. It was observed for the first time that time-integrated spectra exhibited dual photoluminescence. In the time interval right after the excitation, a short-lifetime emission corresponding to the bandgap energy was observed, whose lifetime was estimated to be several tens of ps. Moreover, another emission of smaller energy than the bandgap was observed in the following time interval. This emission had relatively longer lifetime: several hundred ps. These results indicated that at least two types of excitons were formed in the films. Both of these could be the self-trapped excitons generated at the recombination sites with different local environments. Polyterthiophene contains many microcrystalline regions in comparison with polybithiophene. Enhancement of the longer-lifetime photoluminescence (PL) component in polyterthiophene suggests that the exciton with longer lifetime is generated in the microcrystalline region.