Ultrafast carrier dynamics on conjugated poly(3-hexylthiophene)/[6,6]-phenylC61-butyric acid methyl ester composites

The authors have studied ultrafast carrier dynamics on poly(3-hexylthiophene)/[6,6]-phenylC(61)-butyric acid methyl ester (PCBM) composites up to 50% PCBM concentration. They have resolved the exciton intraband relaxation of composites as well as the subsequent electron/polaron relaxation of dissociated excitons. The observed fast time constant of intraband relaxation is found to be 0.5-1.5 ps, whereas the second long-live relaxation (0.5-1 ns) is strongly fullerene related. A wavelength dependent ultrafast study is performed giving fundamental information on the nonradiative exciton relaxation, exciton dissociation, and electron relaxation of PCBM-related states.