HIGH LUMINOUS EFFICIENCY THIN-FILM ELECTROLUMINESCENT DEVICES WITH LOW RESISTIVITY INSULATING MATERIALS

In order to fabricate high brightness and high efficiency thin-film electroluminescent (EL) devices, the emission characteristics of devices employing low resistivity and high dielectric constant materials, such as radio-frequency-sputtered HfO2 films, have been studied. It was found that the EL device with a glass/indium tin oxide/BaTiO3/ZnS:TbF3/HfO2/Ta2O5/HfO2/Al structure exhibited higher brightness and higher efficiency than the other devices. The highest luminous efficiency (eta) and brightness of 0.9 lm/W and 1000 cd/m2, respectively, were obtained at 1-kHz sinusoidal wave voltage excitation. This was mainly due to the insulating layers adjacent to the active layer, which have low resistivity and high dielectric constant. So, it has higher density of interface states and deeper interface states at HfO2-ZnS and BaTiO3-ZnS interfaces.