Simple color tuning of phosphorescent dendrimer light emitting diodes

A simple way of tuning the emission color in solution processed phosphorescent organic light emitting diodes is demonstrated. For each color a single emissive spin-coated layer consisting of a blend of three materials, a fac-tris(2-phenylpyridyl)iridium (III) cored dendrimer (Ir-G1) as the green emitter, a heteroleptic [bis (2-phenylpyridyl) -2- (2′ -benzo [4,5-α] thienyl) pyridyl] iridium (III) cored dendrimer [Ir (ppy)2 btp] as the red emitter, and 4, 4′ -bis(N-carbazolyl) biphenyl (CBP) as the host was employed. By adjusting the relative amount of green and red dendrimers in the blends, the color of the light emission was tuned from green to red. High efficiency two layer devices were achieved by evaporating a layer of electron transporting 1,3,5-tris(2-N-phenylbenzimidazolyl)benzene (TPBI) on top of the spin-coated emissive layer. A brightness of 100 cd m2 was achieved at drive voltages in the range 5.3-7.3 V. The peak external efficiencies at this brightness ranged from 31 cdA (18 lmW) to 7 cdA (4 lmW).