Electrodeless time-resolved microwave conductivity study of charge-carrier photogeneration in regioregular poly(3-hexylthiophene) thin films

The electrodeless flash-photolysis time-resolved microwave conductivity technique (FP-TRMC) has been used to study the photogeneration of charge carriers in spin-coated films of regioregular poly(3hexylthiophene) sP3HTd, over the photon energy range from 1.9 to 5.2 eV for incident light intensities from 10 13 to 10 16 photons/ cm 2 per s 3n sd pulse. The initial, single-photon quantum yield of photoionization, f, has been estimated from the low-intensity limit to the photoconductivity based on a charge carrier mobility of 0.014 cm 2 /V s(determined in separate pulse-radiolysis TRMC experiments on bulk P3HT). The value of f is constant at s1.7± 0.4 d% within the range 1.9‐ 3.0 eV, which encompasses the first electronic absorption band of P3HT. Above 3.0 eV, f increases, up to a value of s 7±2 d% at 5.2 eV. The activation energy of the photoconductivity was found to be approximately 50 meV at all photon energies. The high-intensity, sublinear dependence of the photoconductivity can be described by the occurrence of either exciton-exciton annihilation or diffusional charge recombination with rate coefficients of 2.33 10 ˛8 cm 3 / s and 1.1 3 10 ˛8 cm 3 /s.