Difference in Doping Effects of C₆₀ and C₇₀ in Poly(3-hexylthiophene)

C 60 (Buckminsterfullerene) can be an acceptor dopant for poly(3-hexylthiophene), inducing marked changes in optical absorption and photoluminescence due to charge transfer from polymer to C 60 upon doping. Electrical conductivity also changes to some extent upon C 60 doping. In contrast, C 70 is not effective as a strong dopant in poly(3-hexylthiophene). That is, the absorption spectrum does not change markedly upon C 70 doping and the change in electrical conductivity is also found to be much smaller than in the case of C 60 doping. However, photo-luminescence is markedly quenched upon C 70 doping, just as in the case of C 60 doping. These results are discussed by accounting for the difference in electronic energy states of both C 60 and C 70 relative to that of poly(3-hexylthiophene). The important role of photoinduced charge transfer for quenching of photoluminescence is discussed and C 70 is proposed to be a good sensitizer for photoconductivity of poly(3-alkylthiophene).

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