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1.
Yu Wang Yu Teng Po Lu Xinyu Shen Pei Jia Min Lu Zhifeng Shi Bin Dong William W. Yu Yu Zhang 《Advanced functional materials》2020,30(19)
The external quantum efficiencies (EQEs) of perovskite quantum dot light‐emitting diodes (QD‐LEDs) are close to the out‐coupling efficiency limitation. However, these high‐performance QD‐LEDs still suffer from a serious issue of efficiency roll‐off at high current density. More injected carriers produce photons less efficiently, strongly suggesting the variation of ratio between radiative and non‐radiative recombination. An approach is proposed to balance the carrier distribution and achieve high EQE at high current density. The average interdot distance between QDs is reduced and this facilitates carrier transport in QD films and thus electrons and holes have a balanced distribution in QD layers. Such encouraging results augment the proportion of radiative recombination, make devices with peak EQE of 12.7%, and present a great device performance at high current density with an EQE roll‐off of 11% at 500 mA cm?2 (the lowest roll‐off known so far) where the EQE is still over 11%. 相似文献
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Kuo‐Ju Chen Hsin‐Chu Chen Kai‐An Tsai Chien‐Chung Lin Hsin‐Han Tsai Shih‐Hsuan Chien Bo‐Siao Cheng Yung‐Jung Hsu Min‐Hsiung Shih Chih‐Hao Tsai His‐Hsin Shih Hao‐Chung Kuo 《Advanced functional materials》2012,22(24):5138-5143
Colloidal quantum‐dot light‐emitting diodes (QDLEDs) with the HfO2/SiO2‐distributed Bragg reflector (DBR) structure are fabricated using a pulsed spray coating method. Pixelated RGB arrays, 2‐in. wafer‐scale white light emission, and an integrated small footprint white light device are demonstrated. The experimental results show that the intensity of red, green, and blue (RGB) emission exhibited considerable enhancement because of the high reflectivity in the UV region by the DBR structure, which subsequently increases the use in the UV optical pumping of RGB QDs. A pulsed spray coating method is crucial in providing uniform RGB layers, and the polydimethylsiloxane (PDMS) film is used as the interface layer between each RGB color to avoid cross‐contamination and self‐assembly of QDs. Furthermore, the chromaticity coordinates of QDLEDs with the DBR structure remain constant under various pumping powers in the large area sample, whereas a larger shift toward high color temperatures is observed in the integrated device. The resulting color gamut of the proposed QDLEDs covers an area 1.2 times larger than that of the NTSC standard, which is favorable for the next generation of high‐quality display technology. 相似文献
3.
Wei Deng Xiuzhen Xu Xiujuan Zhang Yedong Zhang Xiangcheng Jin Liang Wang Shuit‐Tong Lee Jiansheng Jie 《Advanced functional materials》2016,26(26):4797-4802
Organometal halide perovskites quantum dots (OHP‐QDs) with bright, color‐tunable, and narrow‐band photoluminescence have significant advantages in display, lighting, and laser applications. Due to sparse concentrations and difficulties in the enrichment of OHP‐QDs, production of large‐area uniform films of OHP‐QDs is a challenging task, which largely impedes their use in electroluminescence devices. Here, a simple dip‐coating method has been reported to effectively fabricate large‐area uniform films of OHP‐QDs. Using this technique, multicolor OHP‐QDs light‐emitting diodes (OQ‐LEDs) emitting in blue, blue‐green, green, orange, and red color have been successfully produced by simply tuning the halide composition or size of QDs. The blue, green, and red OQ‐LEDs exhibited, respectively, a maximum luminance of 2673, 2398, and 986 cd m?2 at a current efficiency of 4.01, 3.72, and 1.52 cd A?1, and an external quantum efficiency of 1.38%, 1.06%, and 0.53%, which are much better than most LEDs based on OHP films. The packaged OQ‐LEDs show long‐term stability in air (humidity ≈50%) for at least 7 d. The results demonstrate the great potential of the dip‐coating method to fabricate large‐area uniform films for various QDs. The high‐efficiency OQ‐LEDs also demonstrate the promising potential of OHP‐QDs for low‐cost display, lighting, and optical communication applications. 相似文献
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Jia‐Yi Sun Freddy T. Rabouw Xian‐Feng Yang Xie‐Yi Huang Xi‐Ping Jing Shi Ye Qin‐Yuan Zhang 《Advanced functional materials》2017,27(45)
Recently developed CsPbX3 (X = Cl, Br, and I) perovskite quantum dots (QDs) hold great potential for various applications owing to their superior optical properties, such as tunable emissions, high quantum efficiency, and narrow linewidths. However, poor stability under ambient conditions and spontaneous ion exchange among QDs hinder their application, for example, as phosphors in white‐light‐emitting diodes (WLEDs). Here, a facile two‐step synthesis procedure is reported for luminescent and color‐tunable CsPbX3–zeolite‐Y composite phosphors, where perovskite QDs are encapsulated in the porous zeolite matrix. First zeolite‐Y is infused with Cs+ ions by ion exchange from an aqueous solution and then forms CsPbX3 QDs by diffusion and reaction with an organic solution of PbX2. The zeolite encapsulation reduces degradation and improves the stability of the QDs under strong illumination. A WLED is fabricated using the resulting microscale composites, with Commission Internationale de I'Eclairage (CIE) color coordinates (0.38, 0.37) and achieving 114% of National Television Standards Committee (NTSC) and 85% of the ITU‐R Recommendation BT.2020 (Rec.2020) coverage. 相似文献
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《Advanced functional materials》2018,28(33)
Substrates with high transmittance and high haze are desired for increasing the light outcoupling efficiency of organic light‐emitting diodes (OLEDs). However, most of the polymer films used as substrate have high transmittance and low haze. Herein, a facile route to fabricate a built‐in haze glass‐fabric reinforced siloxane hybrid (GFRH) film having high total transmittance (≈89%) and high haze (≈89%) is reported using the scattering effect induced by refractive index contrast between the glass fabric and the siloxane hybrid (hybrimer). The hybrimer exhibiting large refractive index contrast with the glass fabric is synthesized by removing the phenyl substituents. Besides its optical properties, the hazy GFRH films exhibit smooth surface (Rsq = 0.2 nm), low thermal expansion (13 ppm °C−1), high chemical stability, and dimensional stability. Owing to the outstanding properties of the GFRH film, OLED is successfully fabricated onto the film exhibiting 74% external quantum efficiency enhancement. The hazy GFRH's unique optical properties, excellent thermal stability, outstanding dimensional stability, and the ability to perform as a transparent electrode enable them as a wide ranging substrate for the flexible optoelectronic devices. 相似文献
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Santanu Pradhan Mariona Dalmases Ayse‐Bilgehan Baspinar Gerasimos Konstantatos 《Advanced functional materials》2020,30(39)
Unbalanced charge injection is deleterious for the performance of colloidal quantum dot (CQD) light‐emitting diodes (LEDs) as it deteriorates the quantum efficiency, brightness, and operational lifetime. CQD LEDs emitting in the infrared have previously achieved high quantum efficiencies but only when driven to emit in the low‐radiance regime. At higher radiance levels, required for practical applications, the efficiency decreased dramatically in view of the notorious efficiency droop. Here, a novel methodology is reported to regulate charge supply in multinary bandgap CQD composites that facilitates improved charge balance. The current approach is based on engineering the energetic potential landscape at the supra‐nanocrystalline level that has allowed to report short‐wave infrared PbS CQD LEDs with record‐high external quantum efficiency in excess of 8%, most importantly, at a radiance level of ≈5 W sr?1 m2, an order of magnitude higher than prior reports. Furthermore, the balanced charge injection and Auger recombination reduction has led to unprecedentedly high operational stability with radiance half‐life of 26 068 h at a radiance of 1 W sr?1 m?2. 相似文献
8.
Bin Xie Haochen Liu Run Hu Chaofan Wang Junjie Hao Kai Wang Xiaobing Luo 《Advanced functional materials》2018,28(30)
Although quantum dots (QDs) show excellent advantages in flexible wavelength‐tuning and high color rendering capability in white light‐emitting diodes (WLEDs) lighting and display applications, the less‐than‐one quantum efficiency inevitably gives rise to a non‐negligible heat generation problem, which induces high‐temperature quenching issues of QDs and severely hinders their potential applications. Efficient heat dissipation for these nanoscale QDs is challenging since these nanoparticle “heat sources” are usually embedded in a low‐thermal conductivity polymer matrix. In this work, this problem is attempted by targeting cooling of the QDs in the silicone matrix by electrostatically bonding the hexagonal boron nitride (hBN) platelets onto QDs without sacrificing the optical performance of WLEDs. The red‐emissive QDs/hBN composites are mixed with yellow‐emissive phosphor to fabricate QDs/hBN‐WLEDs. Due to the effective heat transfer channels established by the QDs/hBN in the silicone, the heat could be dissipated efficiently to ambient air, and the working temperature of WLEDs is reduced by 22.7 °C at 300 mA. The QDs/hBN‐WLEDs still maintain a high luminous efficiency of 108.5 lm W?1 and a high color rendering index of Ra > 95, R9 > 90, showing that the present strategy can improve heat dissipation without sacrificing the optical performance. 相似文献
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White‐Light‐Emitting Diodes: Targeting Cooling for Quantum Dots in White QDs‐LEDs by Hexagonal Boron Nitride Platelets with Electrostatic Bonding (Adv. Funct. Mater. 30/2018) 
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下载免费PDF全文 Bin Xie Haochen Liu Run Hu Chaofan Wang Junjie Hao Kai Wang Xiaobing Luo 《Advanced functional materials》2018,28(30)
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Paul‐Anton Will Maximilian Schmidt Kai Eckhardt Florian Wisser Simone Lenk Julia Grothe Stefan Kaskel Sebastian Reineke 《Advanced functional materials》2019,29(20)
Organic light‐emitting diodes (OLEDs) are widely used in research and are established in the industry. The building block nature of organic compounds enables a vast variety of materials. On top of that, there exist many strategies to improve the light outcoupling of OLEDs making a direct comparison of outcoupling technologies difficult. Here, a novel approach is introduced for the evaluation of light outcoupling structures. The new defined “efficiency of light outcoupling structures” (ELOS) clearly determines the effectiveness of the light outcoupling structure by weighting the experimental efficiency enhancement over the theoretical outcoupling gain. It neither depends on cavity design nor on the chosen organic material. The methodology is illustrated for red phosphorescent OLEDs comprising internal and external light outcoupling structures. Assumptions and further uses are discussed with respect to experimental and theoretical handling. In addition, the ELOS is calculated for various outcoupling techniques from literature to demonstrate the universality. Finally, most suitable reference OLEDs are discussed for application of light outcoupling structures. The presented approach enables new possibilities for studying light outcoupling structures and improves their comparability in a highly material‐driven research field. 相似文献
11.
《Advanced functional materials》2017,27(4)
Highly efficient bright green‐emitting Zn? Ag? In? S (ZAIS)/Zn? In? S (ZIS)/ZnS alloy core/inner‐shell/shell quantum dots (QDs) are synthesized using a multistep hot injection method with a highly concentrated zinc acetate dihydrate precursor. ZAIS/ZIS/ZnS QD growth is realized via five sequential steps: a core growth process, a two‐step alloying–shelling process, and a two‐step shelling process. To enhance the photoluminescence quantum yield (PLQY), a ZIS inner‐shell is synthesized and added with a band gap located between the ZAIS alloy‐core and ZnS shell using a strong exothermic reaction. The synthesized ZAIS/ZIS/ZnS QDs shows a high PLQY of 87% with peak wavelength of 501 nm. Tripackage white down‐converted light‐emitting diodes (DC‐LEDs) are realized using an InGaN blue (B) LED, a green (G) ZAIS/ZIS/ZS QD‐based DC‐LED, and a red (R) Zn? Cu? In? S/ZnS QD‐based DC‐LED with correlated color temperature from 2700 to 10 000 K. The red, green, and blue tripackage white DC‐LEDs exhibit high luminous efficacy of 72 lm W?1 and excellent color qualities (color rendering index (CRI, R a) = 95 and the special CRI for red (R 9) = 93) at 2700 K. 相似文献
12.
Zhimin Luo Guangqin Qi Keyu Chen Min Zou Lihui Yuwen Xinwen Zhang Wei Huang Lianhui Wang 《Advanced functional materials》2016,26(16):2739-2744
Graphene quantum dots (GQDs) with white fluorescence are synthesized by a microwave‐assisted hydrothermal method using graphite as the precursor. A solution‐processed white‐light‐emitting diode (WLED) is fabricated using the as‐prepared white fluorescent GQDs (white‐light‐emitting graphene quantum dots, WGQDs) doped 4,4‐bis(carbazol‐9‐yl)biphenyl as the emissive layer. White‐light emission is obtained from the WLED with 10 wt% doping concentration of WGQDs, which shows a luminance of 200 cd m?2 at the applied voltage of 11–14 V. Importantly, an external quantum efficiency of 0.2% is achieved, which is the highest among all the reported WLED based on GQDs or carbon dots. The results demonstrate that WGQDs as a novel phosphor may open up a new avenue to develop the environmentally friendly WLEDs for practical application in solid‐state lighting. 相似文献
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Highly Efficient Green ZnAgInS/ZnInS/ZnS QDs by a Strong Exothermic Reaction for Down‐Converted Green and Tripackage White LEDs 下载免费PDF全文
下载免费PDF全文 Minji Ko Hee Chang Yoon Heeyeon Yoo Ji Hye Oh Heesun Yang Young Rag Do 《Advanced functional materials》2017,27(4)
Highly efficient bright green‐emitting Zn?Ag?In?S (ZAIS)/Zn?In?S (ZIS)/ZnS alloy core/inner‐shell/shell quantum dots (QDs) are synthesized using a multistep hot injection method with a highly concentrated zinc acetate dihydrate precursor. ZAIS/ZIS/ZnS QD growth is realized via five sequential steps: a core growth process, a two‐step alloying–shelling process, and a two‐step shelling process. To enhance the photoluminescence quantum yield (PLQY), a ZIS inner‐shell is synthesized and added with a band gap located between the ZAIS alloy‐core and ZnS shell using a strong exothermic reaction. The synthesized ZAIS/ZIS/ZnS QDs shows a high PLQY of 87% with peak wavelength of 501 nm. Tripackage white down‐converted light‐emitting diodes (DC‐LEDs) are realized using an InGaN blue (B) LED, a green (G) ZAIS/ZIS/ZS QD‐based DC‐LED, and a red (R) Zn?Cu?In?S/ZnS QD‐based DC‐LED with correlated color temperature from 2700 to 10 000 K. The red, green, and blue tripackage white DC‐LEDs exhibit high luminous efficacy of 72 lm W?1 and excellent color qualities (color rendering index (CRI, Ra) = 95 and the special CRI for red (R9) = 93) at 2700 K. 相似文献
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Organic light‐emitting diodes (OLEDs) have become a mainstream display technology in consumer electronics. Self‐emitting ability, transparency, true dark tone, and capability of being made flexible are some of the features of OLED displays, leading to a superior performance compared with liquid crystal displays. In addition to displays, OLEDs are also a strong candidate for lighting applications. Despite great advances in improving the internal quantum efficiency of an OLED to nearly 100%, the external quantum efficiency is still lacking behind due to optical losses. This review reports the latest advances in the optical design of OLEDs that address the external coupling efficiency of OLEDs. Discussed at first are the fundamentals of OLED optics and how the refractive indices of different layers in an OLED stack affect the extraction efficiency. Then, this paper reviews how microlens arrays, scattering layers, and corrugated structures can be used to recover the optical losses and improve the external efficiency, and the general optical designs for different optical structures for light extraction are presented. 相似文献
17.
Chengxi Zhang Sheng Wang Xiaomin Li Mingjian Yuan Lyudmila Turyanska Xuyong Yang 《Advanced functional materials》2020,30(31)
Lead halide perovskite nanocrystals (PeNCs) are promising materials for applications in optoelectronics. However, their environmental instability remains to be addressed to enable their advancement into industry. Here the development of a novel synthesis method is reported for monodispersed PeNCs coated with all inorganic shell of cesium lead bromide (CsPbBr3) grown epitaxially on the surface of formamidinium lead bromide (FAPbBr3) NCs. The formed FAPbBr3/CsPbBr3 NCs have photoluminescence in the visible range 460–560 nm with narrow emission linewidth (20 nm) and high optical quantum yield, photoluminescence quantum yield (PLQY) up to 93%. The core/shell perovskites have enhanced optical stability under ambient conditions (70 d) and under ultraviolet radiation (50 h). The enhanced properties are attributed to overgrowth of FAPbBr3 with all‐inorganic CsPbBr3 shell, which acts as a protective layer and enables effective passivation of the surface defects. The use of these green‐emitting core/shell FAPbBr3/CsPbBr3 NCs is demonstrated in light‐emitting diodes (LEDs) and significant enhancement of their performance is achieved compared to core only FAPbBr3‐LEDs. The maximum current efficiency observed in core/shell NC LED is 19.75 cd A‐1 and the external quantum efficiency of 8.1%, which are approximately four times and approximately eight times higher, respectively, compared to core‐only devices. 相似文献
18.
Jian Lin Xingliang Dai Xiaoyong Liang Desui Chen Xuerong Zheng Yifei Li Yunzhou Deng Hui Du Yuxun Ye Dong Chen Chen Lin Luying Ma Qinye Bao Haibing Zhang Linjun Wang Xiaogang Peng Yizheng Jin 《Advanced functional materials》2020,30(5)
Solution‐processed oxide thin films are actively pursued as hole‐injection layers (HILs) in quantum‐dot light‐emitting diodes (QLEDs), aiming to improve operational stability. However, device performance is largely limited by inefficient hole injection at the interfaces of the oxide HILs and high‐ionization‐potential organic hole‐transporting layers. Solution‐processed NiOx films with a high and stable work function of ≈5.7 eV achieved by a simple and facile surface‐modification strategy are presented. QLEDs based on the surface‐modified NiOx HILs show driving voltages of 2.1 and 3.3 V to reach 1000 and 10 000 cd m?2, respectively, both of which are the lowest among all solution‐processed LEDs and vacuum‐deposited OLEDs. The device exhibits a T95 operational lifetime of ≈2500 h at an initial brightness of 1000 cd m?2, meeting the commercialization requirements for display applications. The results highlight the potential of solution‐processed oxide HILs for achieving efficient‐driven and long‐lifetime QLEDs. 相似文献
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Jiaojiao Song Ouyang Wang Huaibin Shen Qingli Lin Zhaohan Li Lei Wang Xintong Zhang Lin Song Li 《Advanced functional materials》2019,29(33)
In the study of hybrid quantum dot light‐emitting diodes (QLEDs), even for state‐of‐the‐art achievement, there still exists a long‐standing charge balance problem, i.e., sufficient electron injection versus inefficient hole injection due to the large valence band offset of quantum dots (QDs) with respect to the adjacent carrier transport layer. Here the dedicated design and synthesis of high luminescence Zn1?x CdxSe/ZnSe/ZnS QDs is reported by precisely controlled shell growth, which have matched energy level with the adjacent hole transport layer in QLEDs. As emitters, such Zn1?xCdxSe‐ based QLEDs exhibit peak external quantum efficiencies (EQE) of up to 30.9%, maximum brightness of over 334 000 cd m?2, very low efficiency roll‐off at high current density (EQE ≈25% @ current density of 150 mA cm?2), and operational lifetime extended to ≈1 800 000 h at 100 cd m?2. These extraordinary performances make this work the best among all solution‐processed QLEDs reported in literature so far by achieving simultaneously high luminescence and balanced charge injection. These major advances are attributed to the combination of an intermediate ZnSe layer with an ultrathin ZnS outer layer as the shell materials and surface modification with 2‐ethylhexane‐1‐thiol, which can dramatically improve hole injection efficiency and thus lead to more balanced charge injection. 相似文献