High performance hybrid tandem white organic light-emitting diodes by using a novel intermediate connector

We propose a novel intermediate connector for fluorescence/phosphorescence hybrid tandem white organic light emitting diodes (WOLEDs). The core of our concept is to insert a thin layer of calcium (Ca) between lithium 8-hydroxyquinolinolate (Liq) and 1,4,5,8,9,11-hexaazatriphenylene hexacarbonitrile (HAT-CN) to construct the intermediate connector. The resultant hybrid tandem WOLEDs exhibit very high device performance. For the color-complementary devices, the maximum current efficiency (CE), power efficiency (PE) and external quantum efficiency (EQE) reach 106.3 cd A^-1, 51.4 lm W^-1 and 39.6%, respectively, without any out-coupling techniques. At the luminance intensity of 1000 cd m^-2, the efficiencies can still be maintained at 102.8 cd A^-1, 46.9 lm W^-1 and 38.8%. We also obtain a color rendering index (CRI) as high as 93 in a three-primary-color device. Moreover, both the complementary and three-primary-color devices possess excellent stability for the luminance increased from 1000 cd m^-2 to 10000 cd m^-2.