Electroluminescence from low-dimensionally confined crystals of thiophene/p-phenylene co-oligomers

Organic electroluminescence from epitaxially oriented needle crystals of a thiophene/p-phenylene co-oligomer was studied. The crystals grown by vapor deposition on a KCl (100) surface were confined in a p-sexiphenyl (p-6P) layer. After deposition of an Al cathode the film was wet transferred onto an indium tin oxide (ITO) coated glass. At a low bias voltage, this cell exhibited homogeneous blue light emission from the p-sexiphenyl layer due to carrier recombination in the ITO/p-6P/Al region. With an increase of the voltage, the electroluminescence band shifted to the longer wavelengths corresponding to the green spectrum of the co-oligomer. This emission was concentrated on the needle crystals and suggested that the injected holes were confined inside this low-dimensional structure and recombined with electrons injected from the p-6P layer.