Articles you may be interested inInfluence of carrier conductivity and injection on efficiency and chromaticity in small-molecule white organic lightemitting diodes based on 4 , 4 ′ -bis ( 2 , 2 ′ -diphenylvinyl ) -1 , 1 ′ -spirobiphenyl and rubrene

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We demonstrated efficient red organic light-emitting diodes based on a host emitting system of 9,10-di(2-naphthyl)anthracene (ADN) co-doped with 4-(dicyano-methylene)-2-t-butyle-6-(1,1,7,7-tetramethyl-julolidyl-9-enyl)-4H-pyran (DCJTB) as a red dopant and 2,3,6,7tetrahydro-1,1,7,7-tetramethyl-1H,5H,1 1H-10(2-benzothiazolyl)-quinolizine-[9,9a,1gh] coumarin (C545T) as an assistant dopant. The typical device structure was glass substrate/ITO/4,4 ,4-tris(N-3-methylphenyl-N-phenylamino) triphenylamine(m-MTDATA)/N,N -bis-(naphthalene-1-yl)-N,N -diphenylbenzidine(NPB)/[ADN: DCJTB: C545T/Alq 3 /LiF/Al]. It was found that C545T dopant did not emit by itself but did assist the energy transfer from the host (ADN) to the red emitting dopant. The red OLEDs realized by this approach not only enhanced the emission color, but also significantly improved the EL efficiency. The EL efficiency reached 3.5 cd A −1 at a current density of 20 mA cm −2 , which is enhanced by three times compared with devices where the emissive layer is composed of the DCJTB doped ADN. The saturated red emission was obtained with CIE coordinates (x = 0.618, y = 0.373) at 621 nm, and the device driving voltage is decreased as much as 38%. We attribute these improvements to the assistant dopant (C545T), which leads to the more efficient energy transfer from ADN to DCJTB. These results indicate that the co-doped system is a promising method for obtaining high-efficiency red OLEDs.

We demonstrate highly efficient Alq 3 -based p-i-n organic light-emitting diodes by using cesium carbonate (Cs 2 CO 3 )-doped 4 7-diphyenyl-1, 10-phenanthroline (Bphen) as an electron transport layer, and by using molybdenum trioxide (MoO 3 )-doped N, N -diphenyl-N, N -bis(1,1 -biphenyl)-4,4 -diamine (NPB) as a hole transport layer, which could significantly enhance the electron injection and transport, resulting in a large increase in luminance and efficiency. The maximum luminance, current efficiency and power efficiency reach 23 420 cd cm −2 , 6.4 cd A −1 and 5.3 lm W −1 , respectively, which are much higher than those of the referenced device (without doping). This improvement is attributed to the improved conductivity of the transport layers and the efficient charge balance in the emission zone.

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