Highly efficient yellow organic light emitting diode based on a layer-cross faded emission layer allowing easy color tuning

An easy way to adjust the color of yellow organic light emitting diodes (OLED) is realized by basing the emission layer on a cross-fading zone of two unipolar-conducting host materials doping parts of it either with a red or green phosphorescent emitter at varying thickness ratios. At color coordinates of 0.47/0.50, a current efficacy of 42.2 cd/A (16.2% external quantum efficiency) and a power efficacy of 32.9 lm/W (1000 cd/m2) are measured without light extraction enhancement. Mixed-host emission layer OLED without cross-fading are processed for comparison. Exciton distributions are studied. The concept is suggested to be useful for white OLED.