Picosecond to millisecond photoexcitation dynamics in blends of C60 with poly(p-phenylene vinylene) polymers

We compare photoexcitation dynamics in films of pristine and C-60-mixed 2,5-dioctyloxy poly(p-phenylene vinylene) (DOQ-PPV) using ps transient and cw photoinduced absorption (PA), and PA-detected magnetic resonance (PADMR), We conclude that C-60 doping is relatively inefficient in DOO-PPV. Consequently, the instantaneous exciton photogeneration yield remains high (close to 1) even at high C-60 concentrations. However, as the C-60 concentration increases up to 10 molar percent, the stimulated emission lifetime and cw photoluminescence intensity decrease together by about an order of magnitude due to dissociation of the singlet excitons at C-60 related defect centers into intrachain polaron pairs, which were identified by PADMR. (C) 1998 Elsevier Science B.V.