OBSERVATION OF INTERFACE EXCITONS AND ENERGY-TRANSFER PROCESSES IN AN OLIGO-THIOPHENE MULTILAYER STRUCTURE

The optical properties of a three-layer organic heterostructure consisting of tetrathiophene(T4)/hexathiophene(T6)/tetrathiophene(T4) are investigated by a variety of optical techniques. The optical spectra give strong evidence for the formation of interface exciton states at the interface between adjacent T4 and T6 layers. To our knowledge this is the first time that interface excitons have been experimentally observed in an oligothiophene multilayer structure. Furthermore, evidence of energy transfer from T4 excited states to interface excitons and T6 states is found. Electroluminescence experiments indicate charge confinement and efficient electron-hole recombination in the central T6 layer.