An efficient and bright organic white-light-emitting device

A white-light-emitting device based on molecular organic thin films has been fabricated. The structure of this device is simple, which consists of indium–tin oxide (ITO) anode, a hole transporting layer of N,N′-bis-(1-naphthyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine (NPB) partly doped with 5,6,11,12-tetraphenylnaphthacene (rubrene), as well as light-emitting layer, a hole blocking layer of 2,9-dimethyl,4,7-diphenyl,1,10-phenanthroline (BCP) and an electron transporting layer of tris(8-quinolinolato) aluminum (Alq) and LiF/Al cathode. The partly doped NPB layer and the hole blocking layer (BCP) result in a mixture of lights from NPB molecules (blue-light) and rubrene molecules (orange-light), thereby producing white-light emission. In the device, a thin undoped NPB layer leads to the increase of the device efficiency as a result of the increase of the efficiency of the blue-light-emitting. The chromaticity can be readily adjusted by only varying the thickness of the NPB layer. The CIE coordinates of the device are very close to the equi-energy point and are largely insensitive to the driving voltages. The device has a maximum brightness of 17,000 cd/m2 (at a driving voltage of 22 V), and the maximum electroluminescent (EL) and power efficiency are 3.05 cd/A and 1.92 lm/W (at a drive voltage of 5 V, the current density of 0.5 mA/cm2), respectively.