Photogeneration of confined soliton pairs (bipolarons) in polythiophene

Journal ArticleFrom photoinduced absorption and light-induced electron-spin resonance, we demonstrate that the dominant photocarriers generated in polythiophene with excitation above the energy gap (Eg) are charged bipolarons (spin 0). The observation of bipolarons (B2± ) rather than polarons (Pf ) as the dominant photoexcitations demonstrates that the Coulomb contribution to the bipolaron energy (UB ) is sufficiently small that P± + P± B± 2 . From the analysis of the spectra, we find UB/Eg = 0.12