White Light Emission Obtained by Direct Color Mixing in Multi-Layer Organic Light-Emitting Devices

Three different structures of multi-layer organic light-emitting devices, which consisted of two emitting layers separated by a carrier blocking layer, were investigated. Since the emitting layers are constructed to emit different colors, the colors emitted from the structures are mixed. It was found that the colors were directly mixed in the structures of this study due to the carrier blocking layer sandwiched by the two emissive layers. The blocking layer splits the carrier recombination zone, and with the emission color is controlled by balancing the split. For the white light the CIE coordinate of (0.30, 0.33) is obtained at an applied voltage of 14 V. The luminance is measured to be 1,000 cd/m² at 14 V with the power efficiency of 0.4 lm/W. For a luminance of 100 cd/m² at 11 V, the CIE coordinate is found to be (0.31, 0.34) and the power efficiency was as high as 0.53 lm/W.