Abstract
Exciton and charge dynamics of poly(3-hexylthiophene) (P3HT) blended with covalently linked monomeric (MP), dimeric (BP), or trimeric (TP) fullerene derivatives are investigated by using near-infrared time-resolved absorption spectroscopy under low excitation photon fluence. A low blending ratio (10%, w/w) of the fullerene derivative allows us to examine the effect of linked-fullerene number on charge photogeneration. With reference to P3HT:MP, the P3HT:BP blend shows a one-fold higher exciton dissociation rate and significantly alleviated nongeminate charge recombination in spite of a similar P3HT packing order. However, TP with even larger size tends to aggravate the geminate and nongeminate recombination in picosecond-to-nanosecond time scales. The primary exciton and charge dynamics are discussed in correlation with the nanoscopic film morphology. The results suggest that the dumbbelled fullerene derivative BP as an electron-withdrawing material is promising in boosting the free charge photoproduction in polymer solar cells.
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