Effect of thermal annealing on the lifetime of polymer light-emitting diodes

Kim, Jinook; Lee, Jaeyoon; Han, Chunxi; Lee, Nae Yoon; Chung, In‐Jae

doi:10.1063/1.1582359

Cited by 62 publications

(32 citation statements)

References 11 publications

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“…The maximum luminous efficiency and the half-life of the device using the PEDOT/PSS layer that are obtained after the emitting polymer film was baked at 130°C for 15 min are reasonable values according to the previous literature for devices using green-light-emitting polyfluorene derivatives. [28,29] Therefore, the remarkable improvement indicates that the compositions including perfluorinated ionomers can be one of the promising hole-injection buffer materials for enhancing the device lifetime. Since the fluorocarbon sulfonic acids in the HIL preferentially reside on the film surface, this type of HIL can effectively block the impurities stemming from PEDOT/PSS and ITO (alkali metal, sulfate, In, Sn, etc.).…”

Section: Full Papermentioning

confidence: 99%

Self‐Organized Gradient Hole Injection to Improve the Performance of Polymer Electroluminescent Devices

Lee

Chung

Kwon

et al. 2007

Adv Funct Materials

205

204

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A new approach to forming a gradient hole‐injection layer in polymer light‐emitting diodes (PLEDs) is demonstrated. Single spin‐coating of hole‐injecting conducting polymer compositions with a perfluorinated ionomer results in a work function gradient through the layer formed by self‐organization, which leads to remarkably efficient single‐layer PLEDs (ca. 21 cd A–1). The device lifetime is significantly improved (ca. 50 times) compared with the conventional hole‐injection layer, poly(3,4‐ethylenedioxythiophene)/poly(styrene sulfonate). These results are a good example for demonstrating that the shorter lifetime of PLEDs compared with small‐molecule‐based organic LEDs (SM‐OLEDs) is not mainly due to the inherent degradation of the polymeric emitter itself. Hence, the results open the way to further improvements of PLEDs for real applications to large‐area, high‐resolution, and full‐color flexible displays.

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Section: Full Papermentioning

confidence: 99%

Self‐Organized Gradient Hole Injection to Improve the Performance of Polymer Electroluminescent Devices

Lee

Chung

Kwon

et al. 2007

Adv Funct Materials

205

204

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“…[44][45][46][47] In our device-fabrication process, a toluene solution of WPF-BT-3 (concentration: 15 mg mL -1 ) was spin-coated on a PEDOT: PSS-modified ITO substrate, after which the device was thermally annealed at 70°C for 1 h in vacuum before cathode deposition. The resulting device emitted white light with CIE coordinates of (0.35,0.34), turn-on voltage of 3.5 V, luminance efficiency of 8.99 cd A -1 , power efficiency of 5.75 lm W -1 , external quantum efficiency of 3.8 %, and a maximum brightness of 12 680 cd m -2 .…”

Section: Full Papermentioning

confidence: 99%

White Electroluminescence from a Single‐Polymer System with Simultaneous Two‐Color Emission: Polyfluorene as the Blue Host and a 2,1,3‐Benzothiadiazole Derivative as the Orange Dopant

Liu

Zhou

Cheng

et al. 2006

Adv Funct Materials

193

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New single‐polymer electroluminescent systems containing two individual emission species—polyfluorenes as a blue host and 2,1,3‐benzothiadiazole derivative units as an orange dopant on the main chain—have been designed and synthesized. The resulting single polymers are found to have highly efficient white electroluminescence with simultaneous blue (λmax = 421 nm/445 nm) and orange emission (λmax = 564 nm) from the corresponding emitting species. The influence of the photoluminescence (PL) efficiencies of both the blue and orange species on the electroluminescence (EL) efficiencies of white polymer light‐emitting diodes (PLEDs) based on the single‐polymer systems has been investigated. The introduction of the highly efficient 4,7‐bis(4‐(N‐phenyl‐N‐(4‐methylphenyl)amino)phenyl)‐2,1,3‐benzothiadiazole unit to the main chain of polyfluorene provides significant improvement in EL efficiency. For a single‐layer device fabricated in air (indium tin oxide/poly(3,4‐ethylenedioxythiophene): poly(styrene sulfonic acid/polymer/Ca/Al), pure‐white electroluminescence with Commission Internationale de l'Eclairage (CIE) coordinates of (0.35,0.32), maximum brightness of 12 300 cd m–2, luminance efficiency of 7.30 cd A–1, and power efficiency of 3.34 lm W–1 can be obtained. This device is approximately two times more efficient than that utilizing a single polyfluorene containing 1,8‐naphthalimide moieties, and shows remarkable improvement over the corresponding blend systems in terms of efficiency and color stability. Thermal treatment of the single‐layer device before cathode deposition leads to the further improvement of the device performance, with CIE coordinates of (0.35,0.34), turn‐on voltage of 3.5 V, luminance efficiency of 8.99 cd A–1, power efficiency of 5.75 lm W–1, external quantum efficiency of 3.8 %, and maximum brightness of 12 680 cd m–2. This performance is roughly comparable to that of white organic light‐emitting diodes (WOLEDs) with multilayer device structures and complicated fabrication processes.

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“…[25,26] Therefore, the stability of multilayer whitelight-emitting PLEDs is expected to be better than that of previously reported white-light-emitting PLEDs. [27] Figures 3a,b show the emission spectra obtained from type I and II devices at different applied voltages.…”

mentioning

confidence: 97%

Multilayer Polymer Light‐Emitting Diodes: White‐Light Emission with High Efficiency

Gong¹,

Wang²,

Moses³

et al. 2005

Advanced Materials

469

306

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Organic and polymer light-emitting diodes (OLEDs/ PLEDs) that emit white light are of interest and potential importance for use in active-matrix displays (with color filters) and because they might eventually be used for solid-state lighting. [1,2] In such applications, the fabrication of large-area devices and the use of low-cost manufacturing technology will be the major issues.[2] The fabrication of PLEDs by processing the active materials from solution (e.g., by using printing technology) promises to be less expensive than that of OLEDs, where deposition of the active layers requires the use of vacuum technology. [2,3] Several approaches have been used to generate white light from OLEDs and PLEDs. [2,4±9] In each case, however, the efficiency was modest and the lifetime was limited by that of the blue emitters. [3,7±12] White light is characterized by three quantities: The CIE (Commission Internationale d'Eclairage) coordinates, the color temperature (CT), and the color rendering index (CRI). [13] ªPureº white light has CIE coordinates of (0.333, 0.333), and is obtained by balancing the emission of the colors employed. For illumination applications, the CT needs to be equivalent to that of a blackbody source at temperatures between 3000 and 7500 K. The CRI is a numerical measure of how ªtrueº colors look when viewed with the light source. CRI values range from 0 to 100, with 100 representing true color reproduction.We show that high-performance, multilayer, white-lightemitting PLEDs can be fabricated by using a blend of luminescent semiconducting polymers and organometallic complexes as the emission layer, and water-soluble (or ethanol-soluble) polymers and/or small molecules as the holeinjection/transport layer (HIL/HTL) and the electron injection/transport layer (EIL/ETL). Each layer is spin-cast sequentially from solution. These multilayer PLEDs emit illumination-quality white light with high brightness, high luminous efficiency, suitable CT, stable CIE coordinates, and high CRI.The device fabrication is described in the Experimental section. The device architecture and the molecular structure of the polymers and small molecules used for fabrication of the devices are shown in Scheme 1. The energy levels of the top of the p-band (highest occupied molecular orbital, HOMO) and the bottom of the p*-band (lowest occupied molecular orbital, LUMO) of PFO-ETM, PVK-SO 3 Li, and t-Bu-PBD-SO 3 Na, and the work functions of Ba and PEDOT:PSS are given in Scheme 2a. The corresponding energy levels of PFO-ETM, Ir(HFP) 3 , and fluorenone are shown in Scheme 2b.The selection of materials for the HIL/HTL and EIL/ETL is critical for achieving the band alignment that favors charge injection from the electrodes, for achieving good transport of the respective carriers through the HTL and ETL to the active emission layer, and for hole-blocking (electron-blocking) at the ETL (HTL). PVK-SO 3 Li was selected for the HIL/HTL because its HOMO energy level at ±5.75 eV is well-aligned with the HOMO energy level of PFO-ETM at ±5.80...

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Effect of thermal annealing on the lifetime of polymer light-emitting diodes

Cited by 62 publications

References 11 publications

Self‐Organized Gradient Hole Injection to Improve the Performance of Polymer Electroluminescent Devices

Self‐Organized Gradient Hole Injection to Improve the Performance of Polymer Electroluminescent Devices

White Electroluminescence from a Single‐Polymer System with Simultaneous Two‐Color Emission: Polyfluorene as the Blue Host and a 2,1,3‐Benzothiadiazole Derivative as the Orange Dopant

Multilayer Polymer Light‐Emitting Diodes: White‐Light Emission with High Efficiency

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