Electrical Conductivity and ESR Spectrum of Buckminsterfullerene-Doped Poly(3-alkylthiophene)

Buckminsterfullerene (C60) is effectively doped in poly(3-alkylthiophene). However, the characteristics of C60-doped poly(3-alkylthiophene) are different from the typical behavior observed in the case of conventional dopants. Electrical conductivity of poly(3-alkylthiophene) increases upon C60 doping and decreases again at higher concentration of C60. Its temperature dependence is also anomalous. The absorption spectrum changes markedly upon C60 doping. ESR linewidth decreases from 7.1 G to 1.9 G upon C60 doping. Spin density, evaluated by ESR, is enhanced upon C60 doping. These doping characteristics are tentatively explained by taking electronic energy diagrams of both poly(3-alkylthiophene) and C60 into consideration.