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1.
Artigo em Inglês | MEDLINE | ID: mdl-32227978

RESUMO

Perovskite light-emitting diodes (PeLEDs) exhibit high external quantum efficiencies (EQEs), emerging as a next-generation lighting and display technology. Nevertheless, they suffer from severe efficiency roll-off at high luminance, particularly in the case of blue and green emissions, which is one of the major bottlenecks in their industrial applications. Here, we attack this problem using a rare-earth metal, Yb, as cathode interface layer (CIL) for green PeLEDs. By adopting a new device configuration of ITO/TFB/FA-based quasi-2D perovskite/TPBi/Yb/Ag, we achieved a peak current efficiency (CE) of 22.3 cd/A with a corresponding EQE of 5.28% and a high maximum luminance of 19 160 cd/m2. Importantly, the maximum CE of 22.0 cd/A at 2000 cd/m2 slightly decreased to 16.8 cd/A at 5000 cd/m2 and maintained a still-decent value of 12.0 cd/A at a high luminance of 10 000 cd/m2, exhibiting a remarkably low efficiency roll-off. Our Yb-incorporated devices significantly outperformed the PeLEDs containing conventional CILs, including Mg and Liq, in terms of peak efficiency, efficiency roll-off, and operational lifetime. We attribute this encouraging performance to barrier-free, efficient electron injection enabled by the low work function of Yb (2.6 eV), which led to a high electron current, nearly approaching the hole current in hole-dominant PeLEDs, as confirmed by the single-carrier device measurements. In addition, we also present Yb-incorporated PeLEDs containing Cs-based quasi-2D perovskite as the emissive layer, which displayed an impressive CE of 51.3 cd/A with a corresponding EQE of 16.4% and a maximum luminance of 14 240 cd/m2, and still demonstrated a reduced efficiency roll-off comparing to that of the Liq-based equivalent. These results unveil the inspiring prospects of Yb as an efficient CIL for PeLEDs toward high efficiency with curtailed roll-off.

2.
Small ; 15(31): e1901954, 2019 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-31192532

RESUMO

Metal halide perovskite materials have attracted great attention owing to their fascinating optoelectronic characteristics and low cost fabrication via facile solution processing. One of the potential applications of these materials is to employ them as color-conversion layers (CCLs) for visible blue light to achieve full-color displays. However, obtaining thick perovskite films to realize complete color conversion is a key challenge. Here, the fabrication of micrometer-level thick CsPbBr3 perovskite films is presented through a facile vacuum drying approach. An efficient green photoconversion is realized in a 3.8 µm thick film from blue light @ 463 nm. For a back luminance of 1000 cd m-2 , the brightness of the resulting green emission can reach as high as 200 cd m-2 . Furthermore, only ≈2% of decay in brightness is observed when the films are tested after 18 days of exposure to ambient environment. In addition, a potential design is also proposed for full-color displays with perovskite materials incorporated as CCLs.

3.
Materials (Basel) ; 11(2)2018 Jan 24.
Artigo em Inglês | MEDLINE | ID: mdl-29364836

RESUMO

Flexible, stretchable electroluminescent fibers are of significance to meet the escalating requirements of increasing complexity and multifunctionality of smart electronics. We report a stretchable alternating current electroluminescent (ACEL) fiber by a low-cost and all solution-processed scalable process. The ACEL fiber provides high stretchability, decent light-emitting performance, with excellent stability and nearly zero hysteresis. It can be stretched up to 80% strain. Our ACEL fiber device maintained a stable luminance for over 6000 stretch-release cycles at 50% strain. The mechanical stretchability and optical stability of our ACEL fiber device provides new possibilities towards next-generation stretchable displays, electronic textiles, advanced biomedical imaging and lighting, conformable visual readouts in arbitrary shapes, and novel health-monitoring devices.

4.
Adv Sci (Weinh) ; 4(11): 1700335, 2017 11.
Artigo em Inglês | MEDLINE | ID: mdl-29201628

RESUMO

Bright and stable blue emitters with narrow full-width at half-maxima are particularly desirable for applications in television displays and related technologies. Here, this study shows that doping aluminum (Al3+) ion into CsPbBr3 nanocrystals (NCs) using AlBr3 can afford lead-halide perovskites NCs with stable blue photoluminescence. First, theoretical and experimental analyses reveal that the extended band gap and quantum confinement effect of elongated shape give rise to the desirable blueshifted emission. Second, the aluminum ion incorporation path is rationalized qualitatively by invoking fundamental considerations about binding relations in AlBr3 and its dimer. Finally, the absence of anion-exchange effect is corroborated when green CsPbBr3 and blue Al:CsPbBr3 NCs are mixed. Combinations of the above two NCs with red-emitting CdSe@ZnS NCs result in UV-pumped white light-emitting diodes (LED) with an National Television System Committee (NTSC) value of 116% and ITU-R Recommendation B.T. 2020 (Rec. 2020) of 87%. The color coordinates of the white LED are optimized at (0.32, 0.34) in CIE 1931. The results suggest that low-cost, earth-abundant, solution-processable Al-doped perovskite NCs can be promising candidate materials for blue down-conversion layer in backlit displays.

5.
ACS Appl Mater Interfaces ; 9(8): 7362-7367, 2017 Mar 01.
Artigo em Inglês | MEDLINE | ID: mdl-28194942

RESUMO

The use of interfacial modifiers on cathode or anode layers can effectively reduce the recombination loss and thus have potential to enhance the device performance of polymer solar cells. In this work, we demonstrated that hydroxyl-terminated CuInS2-based quantum dots could be potential cathode interfacial modifiers on ZnO layer for inverted polymer solar cells. By casting of a thin film of CuInS2-based quantum dots onto ZnO layer, the controlled devices show obvious enhancements of open-circuit voltage, short-circuit current, and fill factor. With an optimized interfacial layer with ∼7 nm thickness, an improvement of power conversion efficiency up to 16% is obtained and the optimized power conversion efficiency of PTB7-based (PTB7: poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b']dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl) carbonyl] thieno[3,4-b] thiophenediyl]]) polymer solar cells approaches 8.51%. Detailed analysis shows that the performance enhancement can be explained to the improved light absorption, modified work function, reduced surface roughness, and the increased electron transfer of ZnO cathode interlayer.

6.
Adv Mater ; 28(23): 4727-33, 2016 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-27062394

RESUMO

A new category of deep-absorbing small molecules is developed. Optimized devices driven by mixed additives show a remarkable short-circuit current of ≈20 mA cm(-2) and a highest power conversion efficiency of 9.06%. A multi-length-scale morphology is formed, which is fully characterized by resonant soft X-ray scattering, high-angle annular dark film image transmission electron microscopy, etc.

7.
Chem Sci ; 7(8): 5007-5012, 2016 Aug 01.
Artigo em Inglês | MEDLINE | ID: mdl-30155151

RESUMO

Three new spirofluorene-based hole transport materials, Spiro-S, Spiro-N, and Spiro-E, are synthesized by replacing the para-methoxy substituent in 2,2',7,7'-tetrakis(N,N-di-p-methoxyphenylamine)-9,9'-spirobifluorene (Spiro-MeOTAD) with methylsulfanyl, N,N-dimethylamino and ethyl groups. Their properties as hole transport materials in perovskite solar cells are investigated. The impact of replacing the para-methoxy substituent on bulk properties, such as the photophysical properties, HOMO/LUMO energy level, hole extraction properties and morphologies of perovskite thin films are investigated. Their optoelectronic and charge-transport properties and performance in perovskite solar cells are compared with the current benchmarked and structurally-related hole transport material (HTM) Spiro-MeOTAD. Surprisingly, the methylsulfanyl substituted spirofluorene shows the highest power conversion efficiency of 15.92% among the investigated spirofluorenes, which is an over 38% increase in PCE compared with that of Spiro-MeOTAD under similar device fabrication conditions.

8.
ACS Appl Mater Interfaces ; 7(48): 26405-13, 2015 Dec 09.
Artigo em Inglês | MEDLINE | ID: mdl-26422296

RESUMO

We present an investigation of deep-blue fluorescent polymer light-emitting diodes (PLEDs) with a novel functional 1,3,5-triazine core material (HQTZ) sandwiched between poly(3,4-ethylene dioxythiophene):poly(styrene sulfonic acid) layer and poly(vinylcarbazole) layer as a hole injection layer (HIL) without interface intermixing. Ultraviolet photoemission spectroscopy and Kelvin probe measurements were carried out to determine the change of anode work function influenced by the HQTZ modifier. The thin HQTZ layer can efficiently maximize the charge injection from anode to blue emitter and simultaneously enhance the hole mobility of HILs. The deep-blue device performance is remarkably improved with the maximum luminous efficiency of 4.50 cd/A enhanced by 80% and the maximum quantum efficiency of 4.93%, which is 1.8-fold higher than that of the conventional device without HQTZ layer, including a lower turn-on voltage of 3.7 V and comparable Commission Internationale de L'Eclairage coordinates of (0.16, 0.09). It is the highest efficiency ever reported to date for solution-processed deep-blue PLEDs based on the device structure of ITO/HILs/poly(9,9-dialkoxyphenyl-2,7-silafluorene)/CsF/AL. The results indicate that HQTZ based on 1,3,5-triazine core can be a promising candidate of interfacial materials for deep-blue fluorescent PLEDs.

9.
Macromol Rapid Commun ; 36(18): 1658-63, 2015 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-26175078

RESUMO

Three new star-shaped macromolecules with hexakis(fluoren-2-yl)benzene as the core and pyridine as the periphery (2Py-HFB, 3Py-HFB, and 4Py-HFB) are synthesized and characterized. The synthetic conditions of octacarbonyldicobat-catalyzed cycloaddition reaction for different alkyne precursors are investigated. The coordination interaction between the pyridine ring of alkyne precursor and the cobalt catalyst may result in very low yield of the cyclotrimerization product. However, with the increase of the catalyst loading, the yields of the intermediates of cyclopentadienone are enhanced. Then, the desired cyclotrimerization products can be obtained by the Diels-Alder reactions of cyclopentadienone with acetylene in good yield. These new compounds exhibit good thermal stability and favorable electron affinity. By using the new compounds as electron-transporting materials, all-solution-processed phosphorescent organic light-emitting devices (OLEDs) show good performance with a maximum current efficiency of 5.6 cd A(-1) and maximum external quantum efficiency of 4.68%.


Assuntos
Benzeno/química , Piridinas/química , Transporte de Elétrons
10.
Luminescence ; 30(4): 393-6, 2015 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-25088063

RESUMO

A new europium complex EuL3 (Phen) was used as guest dopant, and a blend of Polyvinylcarbazole and 2-(biphenyl-4-yl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (PVK and PBD) as host matrix. Efficient red organic light-emitting devices (OLEDs) with double-layer structures were manufactured via a solution-processed technique. The guest-doped levels were 1, 3 and 5 wt% relative to the blend mass, respectively. For the 1 wt% doping-level device, the luminous efficiency and luminance were up to 2.96 cd/A and 635.78 cd/m(2) with emissions from both EuL3 (Phen) and from the host; for the 3 wt% doping-level device, the maximum luminous efficiency and luminance were 1.01 cd/A and 370.91 cd/m(2) for the single emission from EuL3 (Phen) only.


Assuntos
Európio/química , Iluminação/instrumentação , Compostos de Bifenilo/química , Carbazóis/química , Luminescência , Oxidiazóis/química , Polivinil/química , Soluções/química
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