The influence of deposition substrate temperature on the performance of organic electroluminescent devices

Organic electroluminescent (EL) devices with a configuration of glass/indium tin oxide (ITO)/α-naphthylphenylbiphenyl amine (NPB)/Tris-(8-hdroxyquinoline) aluminum (Alq₃)/Mg:Ag have been fabricated by vacuum deposition at different substrate temperatures. In some of the devices, the substrate temperature during deposition of the NPB layers is above its glass transition temperature. Raman spectroscopy confirms that the NPB layer so obtained is crystalline. EL performance of the devices have been measured and compared. Contrary to the common believes, substantial increases in luminescent efficiency and brightness have been observed in the devices with a crystalline NPB layer. Storage stability of the devices in air has also been studied