US Patent 7601439 Organic electroluminescent device

An organic electroluminescent device includes an emission layer interposed between a first electrode and a second electrode. The emission layer may be composed of a host material and a phosphorescent dopant material. The host material may be composed of a mixture of a hole transport material and an electron transport material. The hole transport material may be a carbazole compound and the electron transport material may include at least a compound selected from spirofluorenes and organic metal complexes. The use of the mixture facilitates the re-combination of holes and electrons in neighboring organic layers, thus decreasing the driving voltage and increasing the luminous efficiency and lifetime of the organic electroluminescent device.