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

摘要

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(3-hexylthiophene) (P3HT), 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 (3 ns) pulse. The initial, single-photon quantum yield of photoionization, φ, has been estimated from the low-intensity limit to the photoconductivity based on a charge carrier mobility of 0.014 cm~2/Vs (determined in separate pulse-radiolysis TRMC experiments on bulk P3HT). The value of φ is constant at (1.7 ± 0.4)% within the range 1.9-3.0 eV, which encompasses the first electronic absorption band of P3HT. Above 3.0 eV, φ increases, up to a value of (7 ± 2)% 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 2.3 X 10~(-8) cm~3/s and 1.1 X 10~(-8) cm~3/s.