We report here the photoreflectance spectra of the conducting polymer. The interband transition and the transition associated with bipolaron have been observed for the poly (3-mythyl thiophene)-P3MT with different doping densities and under different temperatures, different intensities of modulation light. It was also demonstrated experimentally that the bipolaron may be induced by light with photon energy larger than the band gap Eg of the material, the bipolaron is the intrinsic elementary excitation state which is independent on the way of inducement ( photoinduced or doping-induced); bipolaron may be pinned by ionized impurity and then the confinement parameter will be increased.
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