Abstract
In this study, fabrications of highly color-stable and color-temperature tunable organic light-emitting diodes (OLEDs) are investigated from the viewpoint of device architecture. A highly electroluminescent blue fluorescent emitter 2-(N,N-diphenyl-amino)-6-[4-N,N-diphenyl-amino)styryl]naphthalene (DPASN) is employed as the host and doped with other emitters to fabricate highly color-stable fluorescent white OLED or color-temperature tunable OLED in single-emissive-layer or multi-emissive-layers device architecture. In the first part, the high-efficiency fluorescent blue OLED using DPASN exhibits a power efficiency of 6 lm/W at 100 cd/m2, with CIE coordinates of (0.16, 0.17). Using DPASN as the host and doping an orange emitter of 5,6,11,12-tetra-phenylnaphthacene, a highly efficient and highly color-stable white OLED is fabricated with an efficiency of 9.5 lm/W at 100 cd/m2. The CIE coordinates of which deviate from (0.321, 0.357) to (0.315, 0.344) as the luminance increasing from 100 to 10,000 cd/m2, showing a slight chromaticity deviation of (0.006, 0.013). The device architecture in this white OLED confines electrons and holes effectively within the single emissive layer, preventing recombination zone shift caused by voltage variation and consequently having the emission to be highly color-stable. In addition, the emissive-layer architecture design may prevent excessive exciton quenching on guest, reducing exciton-quench-causing blue shift phenomenon at high voltages. In the second part, DPASN is employed as the host, doped with green emitter of bis[(p-isopropylphenyl)(p-tolyl)amino]-10-10’-phenanthracene and red emitter of 4-(dicyanomethylene)-2-tertbutyl-6-(1,1,7,7-tetramethyljulolidin-4-yl-vinyl-4H-pyran to fabricate color-temperature tunable OLED. The device is capable of yielding an illumination with color-temperature ranging between 2300 and 8200 K, fully covering those of the entire daylight at different times and regions. Opposite to the emissive architecture design of the color-stable device, the color-temperature tunable device employs multi-emissive layers and a thin carrier-modulation layer architecture to have the recombination zone shift along the blue, green and red emissive layers with voltage variation. The recombination core is capable to shift from the cathode side at low voltage to the anode side at high voltage, consequently to have the device yield a relatively wide color-temperature span.