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(3-hexylthiophene) (P3HT), over the photon energy range from 1.9 to 5.20.3em0exeV for incident light intensities from 10¹³ to 10¹⁶ photons∕cm² per (30.3em0exns) 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 0.0140.3em0excm²∕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--3.00.3em0exeV, which encompasses the first electronic absorption band of P3HT. Above 3.00.3em0exeV, φ increases, up to a value of (7±2)% at 5.20.3em0exeV. The activation energy of the photoconductivity was found to be approximately 500.3em0exmeV 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 2.3×10^-80.3em0excm³∕s and 1.1×10^-80.3em0excm³∕s.