Enhanced brightness and efficiency in organic electroluminescent devices using SiO2 buffer layers

Deng, Zhenbo; Ding, Xinyi; Lee, S. T.; Gambling, W.A.

doi:10.1063/1.123809

Cited by 239 publications

(111 citation statements)

References 17 publications

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“…High-efficiency OLEDs have also been reported in various HIL/HTL configurations. [4][5][6][7][8] Furthermore, low-voltage and high-efficiency OLEDs can be realized with a p-doped HIL [9][10][11] in which the layer thickness can be readily adjusted for optimal light extraction. It has been suggested that the enhanced performance in HIL/HTL devices is due to a sequence of cascaded hole-injection barriers present in the HIL/HTL/ETL structure, which produces a "balanced" electron-hole recombination at the HTL/ETL interface.…”

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confidence: 99%

Current efficiency in organic light-emitting diodes with a hole-injection layer

Wang

Klubek

Tang

2008

Applied Physics Letters

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We have systematically investigated the effect of layer structures on the current efficiency of prototypical hole-injection layer ͑HIL͒/hole-transport layer ͑HTL͒/electron-transport layer ͑ETL͒ organic light-emitting diodes based on 4 , 4Ј ,4Љ-tris͓N-͑3-methylphenyl͒-N-phenylamino͔-triphenylamine ͑MTDATA͒ as the HIL, 4 , 4Ј-bis͓N-͑1-naphthyl͒-N-phenylamino͔biphenyl ͑NPB͒ as the HTL, and tris͑8-quinolinolato͒aluminum ͑Alq͒ as the ETL. With bilayer devices, the current efficiency is limited by exciplex emissions in the case of MTDATA/Alq and quenching of Alq emissions by NPB + radical cations in NPB/Alq. The improved current efficiency in trilayer MTDATA/NPB/Alq devices can be attributed to a reduction in NPB + radical cations at the NPB/Alq interface and a strong electric field in the NPB layer. © 2008 American Institute of Physics. ͓DOI: 10.1063/1.2978349͔Since they first appeared in the 1980s, 1 organic lightemitting diodes ͑OLEDs͒ have received much attention due to their potential use as a full-color display technology. Although the efficiency and the operational life of OLEDs have vastly improved through intensive research effort, the mechanism underlying these key performance parameters are not well understood. The basic OLED device has a bilayer organic thin-film structure such as indium tin oxide ͑ITO͒/4,4Ј-bis͓N-͑1-naphthyl͒-N-phenylamino͔biphenyl ͑NPB͒/Alq/LiF/Al, where ITO is the anode and LiF/Al is the cathode, and NPB and Alq are the hole-transport layer ͑HTL͒ and the electron-transport layer ͑ETL͒, respectively. During operation, the injected holes and electrons recombine at or near the HTL/ETL interface, producing electroluminescence ͑EL͒. It has been shown that much improved OLED performance can be realized using a HIL/HTL structure, where HIL is the "hole-injection" layer inserted between the anode and the HTL. For example, with CuPc 2 as the HIL as in CuPc/NPB/Alq where Alq also functions as the emissive layer, long-lived OLEDs have been obtained. Another common HIL material is 4 , 4Ј ,4Љ-tris͓N-͑3-methylphenyl͒-N-phenylamino͔triphenylamine ͑MTDATA͒, 3 with which enhanced current efficiency and operational stability have been demonstrated. High-efficiency OLEDs have also been reported in various HIL/HTL configurations. 4-8 Furthermore, low-voltage and high-efficiency OLEDs can be realized with a p-doped HIL 9-11 in which the layer thickness can be readily adjusted for optimal light extraction. It has been suggested that the enhanced performance in HIL/HTL devices is due to a sequence of cascaded hole-injection barriers present in the HIL/HTL/ETL structure, which produces a "balanced" electron-hole recombination at the HTL/ETL interface. 12,13 In this paper, we systematically investigate the effect of the HIL on OLED performance characteristics, specifically the cause for current efficiency enhancement. Figure 1 shows the multilayer OLED structure and the molecular structures for the HIL ͑MTDATA͒, HTL ͑NPB͒, and ETL ͑Alq͒. The Fabrication of OLEDs by physical vapor deposition is described elsewhe...

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confidence: 99%

Current efficiency in organic light-emitting diodes with a hole-injection layer

Wang

Klubek

Tang

2008

Applied Physics Letters

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“…Thus, the improvement of the optical transmission is needed. Recently some inorganic materials, such as SiO 2 were introduced to OELDs to balance the number of holes and electrons injected to the emitter layer to achieve high recombination efficiencies [13]. An attempt to obtain better electric conduction properties has been made by insertion of a SiO 2 buffer layer between the poly (ethylene terephthalate) (PET) and ITO layers (ITO/SiO 2 /PET) [14].…”

Section: Discussionmentioning

confidence: 99%

Polyimide as a Plastic Substrate for the Flexible Organic Electroluminescent Device

et al. 2004

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In this work, transparent flexible substrates based on polyimides(PI) with indium tin oxide (ITO) thin films for organic electroluminescent devices have been prepared. 2,2'-bis-(3,4-dicarboxyphenyl) hexafluoropropanedianhydride (6FDA) and 2,2'-bis-(trifluoromethyl)-4,4'-diaminobiphenyl (TFDB) PI films were used for transparent flexible substrates. ITO thin films were prepared at two substrate deposition temperatures of 25˚C and 150˚C with a typical radiofrequency (r.f.) planar magnetron sputtering system. The sheet resistance and the optical transmission properties of the fluorinated PI substrate were comparable with those for the slide glass substrate. The substrate properties are better when the deposition temperature is higher. SiO 2 coating onto the fluorinated PI substrate by sol-gel reaction was also attempted to improve the optical transmission of the ITO/PI substrate. It was found that the coating of SiO 2 affected on the morphology of the PI substrates.

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“…The introduced buffer layers mainly can be divided in inorganic and organic compounds. Among the reported inorganic anodic buffer layers good inorganic insulators such as transparent metal oxides Pr 2 O 3 , Y 2 O 3 , Tb 4 O 7 , ZnO (Xu et al, 2001), Al 2 O 3 (Li et al, 1997;Xu et al, 2001), SiO 2 (Deng et al, 1999;Xu et al, 2001), silicon nitride Si 3 N 4 (Jiang et al, 2000;Xu et al, 2001), carbon nitride a-C:N , transition metal oxides, also V 2 O 5 , Guo et al, 2005), MoOx (You et al, 2007;Jiang et al, 2007), WO 3 , Meyer et al, 2007), CuOx, (Hu et al, 2002;Xu et al, 2001), NiO, (Chan et al, 2004;Im et al, 2007) and Ta 2 O 5 (Lu & Yokoyama, 2003), have attracted much attention due to their capability to lower the hole-injection barrier and improve the interface morphology.…”

Section: Hole Transporting and Buffer Layersmentioning

confidence: 99%