Photoconductivity in single crystal polydiacetylene-toluene sulphonate

Abstract

The photoconduction spectrum of the bis(p-toluene sulphonate) ester of 2,4-hexadiyne-1,6-diol (PDA-TS) is reported in the photon energy range 0.62-3.1 eV for conduction along the polymer chain direction. A dominant feature of the spectrum is a steep photoconductive edge at 0.8 eV. This is an agreement with the existence of a localised impurity or defect electron energy level 0.8 eV below the conduction band, if electrons are the majority carriers. Electric field dependence of the photocurrent, examined in the range approximately 15-104 V cm-1, is interpreted on a model which indicates that for current flow parallel and perpendicular to the carbon backbone of the polymer chain, these crystals are model systems for the one- and three-dimensional versions of Onsager's theory (1934) of geminate recombination of bound electron-hole pairs respectively. Also reported are the results of optical transmission measurements on PDA-TS in the photon energy range 0.62-1.84 eV.