A Blue Organic Light Emitting Diode

Abstract

A blue organic light emitting diode (OLED) which has a structure like an SH-B type diode has been developed. The blue OLED consists of a hole-injection layer (m-MTDATA), a hole-transporting emissive layer, a hole-blocking layer and an electron-injection layer (Alq₃) formed on an ITO anode by vacuum vapor deposition. α-NPD was used for the hole-transporting emissive layer, which has an emission peak at around 455 nm. For the hole-blocking layer, we found that 2,9-Dimethyl-4,7-diphenyl-1,10-phenanthroline (Bathocuproine) is a very effective material. As Bathocuproine has a good hole-blocking ability, the recombination area is in the α-NPD layer. The electroluminescence peak from the new blue OLED is at around 455 nm. The color coordinate in CIE chromaticity is (0.15, 0.16). The blue OLED has a potential of over 10,000 cd/m² at 9.5 V under DC operation with an AlLi cathode. When this OLED is driven under a 1/100 duty ratio, the peak luminance is over 54,000 cd/m². The luminous efficiency was 1.1 lm/W at 150 cd/m². The blue OLED device is also a good green device without the Bathocuproine layer. The green OLED shows electroluminescence from the Alq₃ layer with luminance of 40,000 cd/m² at 10 V under DC operation, and the color coordinate in CIE chromaticity is (0.33, 0.55).