Bleaching probe spectroscopy performed for regioregular poly(3-hexylthiophene) diodes reveals that coexistent morphological phases determine the conducting and optical properties of conjugated polymer films. Photoinduced absorption measurements demonstrate that exciton migration occurs from lamella aggregates to morphological sites consisting of quasiuncoupled chains and that the latter sites determine steady-state photophysical properties. Spectroscopy synchronized with diode operation reveals that the morphological locations of injected carriers in polymer diodes vary with the applied bias.

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Excitons, photocarriers, and bias-induced carriers in regioregular poly(3-alkylthiophene) (P3AT) films were investigated using a variety of spectroscopic techniques, such as continuous-wave-(cw-) and femtosecond (fs-) transient photoinduced absorption (PIA) and device modulation (DM) spectroscopies. Comparison between the cw PIA and DM spectra of the poly(3-hexylthiophene) (P3HT) film reveals that photocarriers generated by cw photoexcitation are dominated by localized polarons, whereas charge injection primarily creates delocalized polarons. The photoexcitation intensity dependence of the cw PIA signals demonstrates that both localized and delocalized photogenerated polarons obey a bimolecular recombination process under cw photoexcitation. The proportion of polarons generated by cw photoexcitation in the P3HT film is estimated to be 1/(1+0.137 I 1/2) for I (mW/cm 2) by comparison of the spectral intensities between the DM and cw PIA spectra. DM spectroscopy reveals that both localized and delocalized polarons rapidly increase at a rise point of the bias current. The cw PIA bleaching spectra of P3AT films are shown to vary with the length of the alkyl sidechains of P3AT and be almost reproduced using a single Huang-Rhys factor. The Huang-Rhys factors obtained reveal a trend that the electron-phonon couplings of final exciton migration sites become strong with the increase in the interlamella distance in the P3AT film, which indicates that interlamella couplings affect the electron-phonon couplings of the migration sites located at two-dimensional lamellas.

The photophysics of the regioregular (RR) poly(3‐alkylthiophene) (P3AT) films is investigated by cw‐photoinduced absorption (PIA) measurements based on bleaching signals. The photoexcitation intensity dependence of the cw‐PIA signals demonstrates that both photogenerated localized and delocalized polarons obey a bimolecular recombination process under cw photoexcitation. It is demonstrated that the lineshape of cw‐PIA bleaching spectra for the P3AT films varies with the length of the alkyl substituents of P3AT. The bleaching spectra reveal a trend that the electron‐phonon couplings of final exciton migration sites become strong with increasing the interlamella distance in the P3AT film. This indicates that interlamella couplings affect the electron‐phonon couplings of the migration sites locating at two‐dimensional lamellas. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)