PICOSECOND PHOTOEXCITATION DYNAMICS IN POLY(3-BUTYL-THIOPHENE) FILMS

We have studied photoexcitation dynamics in thin films of poly(3-butyl -thiophene) [P3BT] using ps transient and cw photomodulation technique s, streak camera imaging, electroabsorption and optically detected mag netic resonance spectroscopies. We have determined that intrachain exc itons are tile primary photoexcitations with a characteristic transien t photomodulation spectrum consisting of two photoinduced absorption b ands in the near IR spectral range and a broad stimulated emission ban d in the visible spectral region. The photogenerated excitons are rela tively short-lived (150 ps) and can subsequently decay into polaron pa irs and triplets, which are longer-lived excitations with lifetimes of order ms. We do not find stimulated emission in very thin P3BT films and this is attributed to high defect concentration close to the film surface. (C) 1998 Published by Elsevier Science B.V.