NanoPhotonica

Orlando, FL, United States

NanoPhotonica

Orlando, FL, United States

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Shen H.,Henan University | Bai X.,Henan University | Wang A.,Henan University | Wang H.,Henan University | And 6 more authors.
Advanced Functional Materials | Year: 2014

High-quality violet-blue emitting ZnxCd1-xS/ZnS core/shell quantum dots (QDs) are synthesized by a new method, called "nucleation at low temperature/shell growth at high temperature". The resulting nearly monodisperse ZnxCd1-xS/ZnS core/shell QDs have high PL quantum yield (near to 100%), high color purity (FWHM) <25 nm), good color tunability in the violet-blue optical window from 400 to 470 nm, and good chemical/photochemical stability. More importantly, the new well-established protocols are easy to apply to large-scale synthesis; around 37 g ZnxCd1-xS/ZnS core/shell QDs can be easily synthesized in one batch reaction. Highly efficient deep-blue quantum dot-based light-emitting diodes (QD-LEDs) are demonstrated by employing the Zn xCd1-xS/ZnS core/shell QDs as emitters. The bright and efficient QD-LEDs show a maximum luminance up to 4100 cd m-2, and peak external quantum efficiency (EQE) of 3.8%, corresponding to 1.13 cd A -1 in luminous efficiency. Such high value of the peak EQE can be comparable with OLED technology. These results signify a remarkable progress, not only in the synthesis of high-quality QDs but also in QD-LEDs that offer a practicle platform for the realization of QD-based violet-blue display and lighting. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Shen H.,Henan University | Wang S.,Henan University | Wang H.,Henan University | Niu J.,Henan University | And 6 more authors.
ACS Applied Materials and Interfaces | Year: 2013

High-quality blue-green emitting ZnxCd1-xS 1-ySey/ZnS core/shell quantum dots (QDs) have been synthesized by a phosphine-free method. The quantum yields of as-synthesized ZnxCd1-xS1-ySey/ZnS core/shell QDs can reach 50-75% with emissions between 450 and 550 nm. The emissions of such core/shell QDs are not susceptible to ligand loss through the photostability test. Blue-green light-emitting diodes (LEDs) based on the low-cadmium Zn xCd1-xS1-ySey/ZnS core/shell QDs have been successfully demonstrated. Composite films of poly[9,9- dioctylfluorene-co-N-[4-(3-methylpropyl)]-diphenylamine] (TFB) and ZnO nanoparticle layers were chosen as the hole-transporting and the electron-transporting layers, respectively. Highly bright blue-green QD-based light-emitting devices (QD-LEDs) showing maximum luminance up to 10000 cd/m 2, in particular, the blue QD-LEDs show an unprecedentedly high brightness over 4700 cd/m2 and peak external quantum efficiency (EQE) of 0.8%, which is the highest value ever reported. These results signify a remarkable progress in QD-LEDs and offer a practicable platform for the realization of QD-based blue-green display and lighting. © 2013 American Chemical Society.


Yang Y.,NanoPhotonica | Zheng Y.,NanoPhotonica | Cao W.,University of Florida | Titov A.,NanoPhotonica | And 6 more authors.
Nature Photonics | Year: 2015

We report a full series of blue, green and red quantum-dot-based light-emitting devices (QD-LEDs), all with high external quantum efficiencies over 10%. We show that the fine nanostructure of quantum dots - especially the composition of the graded intermediate shell and the thickness of the outer shell - plays a very important role in determining QD-LED device performance due to its effects on charge injection, transport and recombination. These simple devices have maximum current and external quantum efficiencies of 63 cd A-1 and 14.5% for green QD-LEDs, 15 cd A-1 and 12.0% for red devices, and 4.4 cd A-1 and 10.7% for blue devices, all of which are well maintained over a wide range of luminances from 102 to 104 cd m-2. All the QD-LEDs are solution-processed for ease of mass production, and have low turn-on voltages and saturated pure colours. The green and red devices exhibit lifetimes of more than 90,000 and 300,000 h, respectively. © 2015 Macmillan Publishers Limited. All rights reserved.


A method for synthesizing a quantum dot light emitting diode by providing a glass substrate. A QD-LED stack is formed upon the glass substrate. This QD-LED stack is diffused with an active reagent. The QD-LED stack is encapsulated with a curable resin. The curable resin is cured with UV light.


A quantum dot for emitting light under electrical stimulation has a center of a first composition and a surface of a second composition. The second composition is different than the first composition. An intermediate region extends between the center and surface and has a continuous composition gradient between the center and the surface. The quantum dot is synthesized in a one pot method by controlling the rate and extent of a reaction by controlling the following parameters: (i) type and quantity of reactant, (ii) reaction time, and (iii) reaction temperature.


Grant
Agency: NSF | Branch: Standard Grant | Program: | Phase: | Award Amount: 180.00K | Year: 2013

This Small Business Innovation Research Phase I project seeks to demonstrate ultra high efficiency quantum dot light-emitting diodes (QD-LEDs) using a top-emitting structure and micro-lens array for display applications. Two key challenges will be addressed. First, a novel top-emitting structure will be explored based on the previous efficient bottom-emitting QD-LEDs. Use of top-emitting structure removes light trapped through the wave-guide mode within the glass substrate, which improves light out-coupling. A micro-lens array will be applied on top of the QD-LEDs to further enhance the light extraction. The project will focus on a number of innovative approaches. Micro-lens arrays will be fabricated using a novel stamp printing method. A small size micro-lens along with a top-emitting structure will minimize the pixel blurring effect induced by the conventional out-coupling micro-lens. Secondly, high refractive index material will be used to fabricate a micro-lens to match the refractive index of the transparent electrode, hence improving light extraction efficiency.

The broader impact/commercial potential of this project lies is to enable the commercialization of QD-LED displays, solid-state lighting and other applications. QD-LEDs provide intrinsically higher color purity compared to LCD or organic light-emitting diode (OLED) technology and are suitable for display applications. However, current QD-LED solutions suffer from lower efficiency compared to LCD and OLED. The company?s innovative nanomaterials and device architecture has enabled very efficient bottom-emitting QD-LEDs with high external quantum efficiency. Additionally, the multi-layer structure in the company?s QD-LED are deposited through solution processing, which reduces the cost significantly. It is expected that a better performing and substantially less expensive QD-LED will quickly gain considerable market share in a $60B market that ships over 1.5B units a year.


Grant
Agency: NSF | Branch: Standard Grant | Program: | Phase: SMALL BUSINESS PHASE II | Award Amount: 1.27M | Year: 2014

This Small Business Innovation Research (SBIR) Phase II project aims to further enhance the efficiency and lifetime of quantum dot light emitting diodes (QD-LEDs) used for displays. An active matrix QD-LED prototype display will be demonstrated using solution processing. The lifetime of QD-LED will be extended by determining degradation mechanisms, and development of new materials, modified device processing and encapsulation techniques. The effects of charge imbalance and light trapping on the efficiency of QD-LED will be determined and optimized. External quantum efficiencies will exceed 18%. Lifetimes of QD-LEDs exceeding 10,000 hours for all three primary colors will be demonstrated, which meets the requirement for mobile display applications.

The broader impact/commercial potential of this project will be a demonstration that quantum dot light-emitting diodes (QD-LEDs) have the commercial advantages of high efficiencies and long lifetimes. QD-LED will be welcomed by the display industry which is now desperately searching for next generation technologies. The demonstration of an active matrix QD-LED display prototype with a solution printing process will be a critical step towards the commercialization. The systematic investigation of technical details involved in the printing process of active matrix QD-LEDs will enable the construction of a pilot facility and eventual mass production. The simple architecture and solution fabrication process will provide significant cost advantages over conventional processes.


Grant
Agency: National Science Foundation | Branch: | Program: SBIR | Phase: Phase II | Award Amount: 683.35K | Year: 2014

This Small Business Innovation Research (SBIR) Phase II project aims to further enhance the efficiency and lifetime of quantum dot light emitting diodes (QD-LEDs) used for displays. An active matrix QD-LED prototype display will be demonstrated using solution processing. The lifetime of QD-LED will be extended by determining degradation mechanisms, and development of new materials, modified device processing and encapsulation techniques. The effects of charge imbalance and light trapping on the efficiency of QD-LED will be determined and optimized. External quantum efficiencies will exceed 18%. Lifetimes of QD-LEDs exceeding 10,000 hours for all three primary colors will be demonstrated, which meets the requirement for mobile display applications. The broader impact/commercial potential of this project will be a demonstration that quantum dot light-emitting diodes (QD-LEDs) have the commercial advantages of high efficiencies and long lifetimes. QD-LED will be welcomed by the display industry which is now desperately searching for next generation technologies. The demonstration of an active matrix QD-LED display prototype with a solution printing process will be a critical step towards the commercialization. The systematic investigation of technical details involved in the printing process of active matrix QD-LEDs will enable the construction of a pilot facility and eventual mass production. The simple architecture and solution fabrication process will provide significant cost advantages over conventional processes.


Grant
Agency: National Science Foundation | Branch: | Program: SBIR | Phase: Phase I | Award Amount: 150.00K | Year: 2013

This Small Business Innovation Research Phase I project seeks to demonstrate ultra high efficiency quantum dot light-emitting diodes (QD-LEDs) using a top-emitting structure and micro-lens array for display applications. Two key challenges will be addressed. First, a novel top-emitting structure will be explored based on the previous efficient bottom-emitting QD-LEDs. Use of top-emitting structure removes light trapped through the wave-guide mode within the glass substrate, which improves light out-coupling. A micro-lens array will be applied on top of the QD-LEDs to further enhance the light extraction. The project will focus on a number of innovative approaches. Micro-lens arrays will be fabricated using a novel stamp printing method. A small size micro-lens along with a top-emitting structure will minimize the pixel blurring effect induced by the conventional out-coupling micro-lens. Secondly, high refractive index material will be used to fabricate a micro-lens to match the refractive index of the transparent electrode, hence improving light extraction efficiency. The broader impact/commercial potential of this project lies is to enable the commercialization of QD-LED displays, solid-state lighting and other applications. QD-LEDs provide intrinsically higher color purity compared to LCD or organic light-emitting diode (OLED) technology and are suitable for display applications. However, current QD-LED solutions suffer from lower efficiency compared to LCD and OLED. The company?s innovative nanomaterials and device architecture has enabled very efficient bottom-emitting QD-LEDs with high external quantum efficiency. Additionally, the multi-layer structure in the company?s QD-LED are deposited through solution processing, which reduces the cost significantly. It is expected that a better performing and substantially less expensive QD-LED will quickly gain considerable market share in a $60B market that ships over 1.5B units a year.


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