Photogeneration, recombination and transport of charge carriers in a quasi-one-dimensional system

Abstract

In a quasi-one-dimensional system the photogeneration rate for excess free carriers is expected to be dependent on the applied electric field. This leads to a number of novel features in the photoconductive behaviour of a 1D material, particularly in the presence of deep trapping centres. The author describes the expected photoconductive response of such a system in detail as a function of light intensity, polarisation, applied electric field and the direction of current flow. These expectations, valid for all 1D systems, are then compared with the experimental data presented for the quasi-1D single-crystal polymer polydiacetylene-toluene sulphonate. The experimental results indicate that, for the 1D case, the quantum efficiency for free-carrier generation has a minimum non-zero value in the low-field limit which may be comparable with that in the 3D case. This necessitates a modification, in the low-field limit, of the presently accepted 1D version of the Onsager theory of geminate recombination.