DUAL PHOTOLUMINESCENCE OF POLYTHIOPHENE THIN-FILMS

Transient photoluminescence of electrochemically prepared thin films o f polybithiophene and polyterthiophene was analyzed. It was observed f or the first time that time-integrated spectra exhibited dual photolum inescence. In the time interval right after the excitation, a short-li fetime emission corresponding to the bandgap energy was observed, whos e lifetime was estimated to be several tens of ps. Moreover, another e mission of smaller energy than the bandgap was observed in the followi ng time interval. This emission had relatively longer lifetime: severa l hundred ps. These results indicated that at least two types of excit ons were formed in the films. Both of these could be the self-trapped excitons generated at the recombination sites with different local env ironments. Polyterthiophene contains many microcrystalline regions in comparison with polybithiophene. Enhancement of the longer-lifetime ph otoluminescence (PL) component in polyterthiophene suggests that the e xciton with longer lifetime is generated in the microcrystalline regio n. (C) 1998 Elsevier Science S.A. All rights reserved.