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Highly efficient red phosphorescent organic polymer light-emitting diodes (PhOLEDs) were fabricated based on a solution-processed small-molecule host 4,4'-bis(N-carbazolyl)-1,1'-biphenyl (CBP) by doping an iridium complex, tris(1-(2,6-dimethylphenoxy)-4-(4-chlorophenyl)phthalazine)iridium (III) (Ir(MPCPPZ)(3)). A hole blocking layer 1,3,5-tri(1-phenyl-1H-benzo[d]imidazol-2-yl)phenyl (TPBI) with a function of electron transport was thermally deposited onto the top of CBP layer. The diode with the structure of ITO/PEDOT:PSS (50 nm)/CBP:Ir(MPCPPZ)(3) (55 nm)/TPBI (30 nm)/Ba (4 nm)/Al (120 nm) showed an external quantum efficiency (QE(ext)) of 19.3% and luminous efficiency (LE) of 18.3 cd/A at a current density of 0.16 mA/cm(2), and Commission International de l'Eclairage (CIE) coordinates of (0.607, 0.375). It was suggested that the diodes using TPBI layer exhibited nearly 100% internal quantum efficiency and one order magnitude enhanced LE or QE(ext) efficiencies. (c) 2013 Elsevier B.V. All rights reserved.

A high-performance hybrid white organic light-emitting diode (WOLED) based on a simple structure has been developed. The resulting device exhibits a maximum total current efficiency and power efficiency of 35.7 cd/A and 30.6 lm/W, respectively. Even at a high luminance of 1000 cd/m(2), a current efficiency of 32.0 cd/A and a power efficiency of 19.4 lm/W are obtained, suggesting that the device exhibits a low efficiency roll-off. Besides, the device shows excellent color-stability during a wide range of luminance and a high color rendering index (CRI) of 83 is obtained. Moreover, the origin of the superior properties is explored comprehensively. Such achieved results demonstrate that high efficiency, low efficiency roll-off, stable color and high CRI can be simultaneously realized in a simplified hybrid WOLEDs. (C) 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Single-emitting-layer (single-EML) hybrid white organic light-emitting diodes (WOLEDs) have attracted a great deal of attention due to their simplified structures. However, the guest concentration is usually too low, which is quite difficult to control and reproduce in the coevaporation process. Herein, for the first time, N,N′-di(naphthalene-1-yl)-N,N′-diphenyl-benzidine has been used as both the host and the blue emitter in single-EML WOLEDs. By dint of this multifunctional material, the concentration is found to be as high as 1.5%. This device exhibits a maximum total efficiency of 65.3 lm W−1, indicating a significant step towards the real commercialization. Besides, low voltages (i.e., the turn-on voltage is 2.4 V and 3.45 V at 1000 cd m−2) and a color rendering index (CRI) of 77 are obtained for this two-color WOLED. Unlike the working mechanisms in previous single-EML hybrid WOLEDs with low guest concentrations, devices comprising high concentrations exhibit more sophisticated engineering, in which the device smartly allows the utilization of both the fluorescence from the host itself, and the complementary phosphorescence from the guest by incomplete Förster energy transfer, Dexter energy transfer as well as direct exciton formation on the guest. Moreover, we have incorporated this unique host–guest system into a dual-EML hybrid WOLED. Maximum efficiencies of 17.2 lm W−1 and 10.2 lm W−1 at 1000 cd m−2 (3.85 V) with an ultrahigh CRI of 93 are achieved, providing a new opportunity to accomplish the simplified structure/low voltage/high efficiency/ultrahigh CRI trade-off.