Electroluminescence in Thin Films of Organic Dyes

Electroluminescence (EL) in three types of organic thin films, amorphous pyrazoline films prepared by vacuum vapor deposition, cyanine dye multi-layers prepared by the Langmuir-Blodgett method and crystalline perylene films by vacuum vapor deposition, were investigated. The organic thin films were sandwiched between an electron-injection electrode (Al or In) and a hole-injection electrode (Au, Indium-Tin-Oxide, CuI, or poly(3-methylthiophene) film). EL was confirmed to originate from recombination of injected holes and electrons. The poly(3-methylthiophene) electrode was found to be the most excellent for hole infection. By use of this electrode, the threshold voltage for emission markedly lowered. Because the rate of carrier recombination was determined by the efficiency of electron injection, the improvement of an electron-injection electrode brought about a large increase of EL efficiency. In, which possesses low work function, was found to be favorable for an electron-injection electrode