Maximizing Alq/sub 3/ OLED internal and external efficiencies: charge balanced device structure and color conversion outcoupling lenses

In this paper, we report bright, efficient Alq₃-based [tris-(8-hydroxyquinoline) aluminum] organic light-emitting diode (OLED) structures that incorporate hemispherical lenses for increased output power efficiency. The 6-layer hybrid (polymer/small molecule) OLED structure contains two spin-coated polymer layers and four thermally evaporated small molecule layers. This structure results in balanced charge injection, thus leading to a more efficient device. The use of index-matched transparent lenses resulted in luminous and external quantum efficiency of 7.5 lm/W and 8%, respectively. The size and shape of the lens was used to control the angular power distribution. Lenses incorporating color conversion media were used to achieve high OLED efficiency in various colors. Saturated yellow, orange, and red devices with external quantum efficiencies as high ~4% were obtained from this approach