Photoconductivity in single crystal polydiacetylene-toluene sulphonate

Abstract

The photoconduction spectrum of millimetre size single crystals of the solid state polymerised conjugated polymer bis(p-toluene sulphonate) ester of 2,4-hexadiyne-1,6-diol (PDA-TS) are 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 in 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, as we recently postulated from the temperature dependence of the dark current.Electric field dependence of the photocurrent, examined in the range -15-104Vcm-', 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 of geminate recombination of bound electron-hole pairs respectively.Also reported here are the results of optical transmission measurements on PDA-TS in the photon energy range 062-1+34 eV.