Bipolar carrier transport in a conjugated polymer by complex admittance spectroscopy

We report the bipolar transport properties of the LUMATION (TM) (Sumitomo Chemical) 1300 Series green-emitting polymer investigated by means of admittance spectroscopy. Analysis of the inductive response in single-carrier polymer diodes yields electron and hole mobilities which are in excellent agreement with the results of independent measurements. Admittance measurements in dual injection diodes, in combination with the analysis of current-voltage characteristics, provide evidence that the dual injection diodes operate in space-charge-limited regime, indicative of strong recombination within the material. Our results provide strong evidence that the space-charge-related admittance response of dual-carrier diodes is dominated by combined electron-hole response, which corresponds to the sum of electron and hole mobilities. This implies that electron and hole mobilities cannot be obtained separately from admittance measurements in space-charge-limited dual-carrier devices. (c) 2006 American Institute of Physics.