Improved electroluminescence from oligothiophenes

Low quantum efficiency of electroluminescence (EL) from solid state evaporated thin films of α-sexithiophene (α-6T) was accounted for by quenching due to inter-chain interaction. The substitution of α-6T by voluminous substituants at the end of the chains led to an increase of the fluorescence 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 bilayer device α-6T/DPS6T improved hole blocking in the recombination region between organic layers leading to creation of excitons away from the Al electrode. By dispersing the molecules in a highly conducting hole transporting host matrix of PVK the efficiency was further improved. Transient EL response of devices indicate that poor electron injection and mobility limits output efficiencies.