Efficient top-emitting white organic light emitting device with an extremely stable chromaticity and viewing-angle

In this paper, we report on the fabrication of a top-emitting electrophosphorescent p - i - n white organic light-emitting diode on the basis of a low-reflectivity Sm/Ag semi-transparent cathode together with a thickness-optimized ZnS out-coupling layer. With a 24-nm out-coupling layer, the reflectivity of the cathode is reduced to 8% at 492 nm and the mean reflectivity is 24% in the visible area. By introducing an efficient electron blocking layer tris(1-phenylpyrazolato,N,C2′)iridium(III) (Ir(ppz) ₃) to confine the exciton recombination area, the current efficiency and the colour stability of the device are effectively improved. A white emission with the Ir(ppz) ₃ layer exhibits a maximum current efficiency of 9.8 cd/A at 8 V, and the Commission Internationale de L'Eclairage (CIE) chromaticity coordinates are almost constant during a large voltage change of 6 V - 11 V. There is almost no viewing angular dependence in the spectrum when the viewing angle is no more than 45°, with a CIE _x,y coordinate variation of only (±0.0025, ±0.0008). Even at a large viewing angle (75°), the CIE _x,y coordinate change is as small as (±0.0087, ±0.0013).