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 techniques, streak camera imaging, electroabsorption and optically detected magnetic resonance spectroscopies. We have determined that intrachain excitons are the primary photoexcitations with a characteristic transient photomodulation spectrum consisting of two photoinduced absorption bands in the near IR spectral range and a broad stimulated emission band in the visible spectral region. The photogenerated excitons are relatively short-lived (150 ps) and can subsequently decay into polaron pairs 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.