OPTICAL-EXCITATIONS OF POLY(3-BUTYLTHIOPHENE) AND HIGH ELECTRON-AFFINITY SUBSTITUTED POLY(3-BUTYLTHIOPHENE)

We have characterized the long lived photoexcitations in thin films of poly(3-butylthiophene) [PBT] and co-polymers made of PBT and acceptor substituted PET, using photo-induced absorption (PA) and optically detected magnetic resonance PA (PADMR) spectroscopies. The PA spectra reveal two main absorption bands; one at 1.4-1.7 eV, which is composed of contributions from both S=1 and S=1/2 species, and another at 0.5 eV which is due to S=1/2 charged species. Our results are explained within a picture where the S=1 species are triplet excitons and the S=1/2 species are photogenerated polarons.