Doping effect of buckminsterfullerene in poly(2,5-dialkoxy-p-phenylene vinylene)

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Abstract
Photoluminescence has been markedly quenched and photoconductivity has been enhanced by more than one order of magnitude upon introduction of several mol% of buckminsterfullerene (C60) to poly(2,5‐dialkoxy‐p‐phenylene vinylene) (RO‐PPV), especially at excitations about 2.2 eV, corresponding to the band gap energy of RO‐PPV and also in bands at 1.8 and 3.5 eV, which correspond to optical excitation of C60 molecules, suggesting that photo‐induced charge transfer occurs between RO‐PPV and C60. On the other hand, absorption spectrum and electrical conductivity of RO‐PPV have been scarcely influenced by doping of small amount of C60, suggesting that the ground state charge transfer between C60 and RO‐PPV is not effective, contrary to the case of poly(3‐hexylthiophene). These results are discussed by taking relative electronic energy states of RO‐PPV and C60 into consideration. The photo‐excited exciton‐polaron (Ex‐P) in RO‐PPV is interpreted to migrate along about 100 monomer units along a polymer main chain in its lifetime and dissociates when encountered with C60. These unique doping characteristics of C60 in RO‐PPV are not dependent on the alkyl chain length, contrary to the case of poly(3‐alkylthiophene).