Improved electroluminescence from oligothiophenes

Low quantum efficiency of electroluminescence (EL) from solid state evapora ted thin films of alpha-sexithiophene (alpha-6T) was accounted for by quenc hing due to inter-chain interaction. The substitution of alpha-6T by volumi nous substituants at the end of the chains led to an increase of the fluore scence in the solid state with a concomitant decrease in conductivity down to 10(-11) S cm(-1) due to the increase in spacing between molecules. A bil ayer device alpha-6T/DPS6T improved hole blocking in the recombination regi on between organic layers leading to creation of excitons away from the Al electrode. By dispersing the molecules in a highly conducting hole transpor ting host matrix of PVK the efficiency was further improved. Transient EL r esponse of devices indicate that poor electron injection and mobility limit s output efficiencies.