Charge-carrier dynamics in polythiophene films studied by in-situ measurement of flash-photolysis time-resolved microwave conductivity (FP-TRMC) and transient optical spectroscopy (TOS)

Abstract

An in-situ measurement system for flash-photolysis time-resolved microwave conductivity (FP-TRMC) and transient optical spectroscopy (TOS) has been developed to perform simultaneous measurements of photo-induced changes in conductivity and charge-carrier density in an organic thin film. The electric field in the resonant cavity designed for the present system was analysed by electrostatic simulation. Using the present system and the simulated electric field, the photoconductivity and transient absorption in a regioregular poly(3-hexyl thiophene) film were measured using one particular geometry under photon excitation energies of 6.39, 4.98, 3.48, and 2.34 eV. The dynamics of photogenerated charge carriers is discussed in terms of the excitation energy and incident photon intensity. The transient absorption spectrum induced by 3.48 eV light is presented and compared with the TRMC transient.

Acknowledgements

The authors thank Professor L. D. A. Siebbeles and Dr M. P. de Hass at IRI, Delft University of Technology, for their advice on FP-TRMC analysis. We also thank Mr S. Ohtomo at Micro Denshi Co. Ltd. for manufacturing the microwave circuit, Mr K. Abe at Canon Inc. for his assistance in experiments and informative discussions, Mr. K. Tahara at AET Japan Inc. for his help in electrostatic analysis, and Dr A. Acharya and Dr Y. Koizumi at ISIR, Osaka University, for their support with the experiments.