DARK-CURRENT MEASUREMENTS IN A CONJUGATED-POLYMER SINGLE-CRYSTAL

Experimental results for the dark current as a function of orientation, potential difference and temperature are reported for millimetre-sized single crystals of the solid-state-polymerised conjugated-polymer bis(p-toluene sulphonate) ester of 2,4-hexadiyne-1, 6-diol (PDA-TS). The results show that the carrier mobility along the polymer chains is 1000 times that perpendicular to the chains. Both ohmic and space-charge-limited conduction are dominated by a localised level 0.80+or-0.02 eV from the band edge and of concentration corresponding to <or=1 centre per metre of chain length. The ohmic conduction is due to impurities donating one excess carrier per 30 metres of chain.