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Invited Paper: Quantum Dot Light Emitting Devicesfor Pixelated Full Color Displays
特邀报告：全彩色显示器量子点发光器件像素化分析
Abstract摘要
Quantum dot light emitting devices (QD-LEDs) developed over thepast four years demonstrate high external quantum efficiencies,saturated visible color emission, narrow-band infra-red emission,and can be fabricated with a scalable fabrication technique of highresolution. 量子点发光器件（QD-LED）的发展，超过过去四年的成就，从高外部量子效率，饱和彩色排放等方面都可可以看见，其窄带红外线发射，可以制作具有可扩展的制造技术并且可以获得高分辨率。These recent advancements of QD-LED technology aredue to progress in the chemistry of colloidal quantum dot synthesisand the development of new fabrication methods for generating thinfilms of QDs as outlined in this letter.
I. Introduction介绍
Quantum dot light emitting devices (QD-LEDs) have built upon theorganic LED (OLED) technology to demonstrate paper-thin lightsources of highly saturated and tunable spectrum.
建立在量子点发光器件（QD-LED）的有机发光二极管（OLED）技术，可以获得像纸一样薄的光源高度饱和度和可调谐的光谱。
In contrast to all-organic OLEDs, the first generation of QD-LEDs [1,2] utilizescolloidal, inorganic, single crystal QD lumophores embedded in anorganic matrix to generate electroluminescence. The quality of theQD lumophores determines the QD-LED performance. It is,therefore, important to note that photoluminescence efficiency of thebest QDs can reach nearly unity efficiency, which can stayunchanged even when QDs are UV-irradiated under caustic aqueousenvironments (environments that quickly degrade luminescenceefficiency of organic luminescent molecules). Furthermore, theluminescent excited state of a QD has a mixed singlet-tripletcharacter, with a typical luminescent lifetime on the order of 10ns to40ns. The mixed-spin exciton character facilitates capture of bothsinglet and triplet excitons from the neighboring donor sites [3].The short luminescence lifetime reduces the likelihood of exciton-exciton annihilation that is manifested in phosphorescent OLEDs athigher current densities. All this suggests that colloidallysynthesized QDs are highly desirable lumophores in electricallypumped structures, motivating the development of QD-LEDs.所有这一切都表明，合成胶体量子点在电泵浦结构是非常可取的，可以推动QD-LED的发光。http://www.ukassignment.org/lxslw/
With development of the QD-LED technology our goal was togenerate a uniform method for manufacturing red, green, blue (R-G-B) [4], and infra-red [5] emissive devices, where the only differencein the device structure of different color emitters is the luminescencecolor of the utilized QDs. We aimed to demonstrate thatelectroluminescence of R-G-B QD-LED satisfies HDTV colorstandards, with the subtended CIE color triangle that exceedsdemonstrated OLED performance [6]. Finally, we needed toaddress the challenge of patterning individual LEDs, and develop amethod that enables QD-LED pattern definition of 25μm (1000 dpi)or better, utilizing a patterning method scalable beyond Gen2mother glass [7].
All of the above challenges have been addressed over the past year.上述所有的挑战在过去的一年中已经得到解决。This manuscript outlines the developed methods starting with thedescription of colloidal QDs (section II) and a method for forming monolayers of QDs in patterned or unpatterned form (sections IIIand IV). The QD layers are then used to fabricate QD-LEDs(section V).量子点层，然后用于制造量子点发光二极管（第五部分）上。
II. Colloidal Quantum DotsInorganic nanocrystal quantum dots (QDs) are semiconductornanoparticles that are chemically synthesized in organic solventsusing simple benchtop techniques891011[8-11]. Sizes of individualQDs can be precisely controlled in a range from 2 to 12 nanometers.The electronic structure of QDs consists of delocalized electron andhole states that are reminiscent of atomic wavefunctions.量子点的电子结构，由这些游离电子及空穴态原子波函数组成。
Theenergy of these states is strongly size-dependent. For example,emission from CdSe QDs can be tuned across the entire visiblespectrum by changing the size of the nanocrystals (Fig. 1).Nanocrystal QDs can be synthesized with narrow size distributionsso that the bandwidth of the luminescence can be < 30 nm. The QDabsorption band is very broad, requiring only that the excitationlight, or energy tranfered excitations, be above the QD band gap.The energy level structure of QDs also differs substantially frommost organic chromophores. The emission from QDs is from alowest energy transition that for CdSe QDs is thought to be partlyspin forbidden, leading to long (10-100 nsec) emission lifetimes atroom temperature (and microseconds at cryogenic temperatures).The dense of states manifold above this emissive state contributes tothe high absorption constant above the band edge.极管上面的这种发射状态有助于极管伤感的高吸收常数。
In a laboratory setting, QDs are grown using solution phasesynthesis. 在实验室环境中，使用溶液相合成，可以使得量子点获得生长。The technique consists of rapidly introducing precursorsinto a boiling organic solvent, where the initial reaction is theformation of nuclei followed by growth of those nuclei to createQDs. The formed core semiconductor QDs are then passivated andprotected by the growth of an inorganic semiconductor shell, forexample CdSe cores can be coated with ZnS shell. A core-shelltype composite rather than organically passivated QDs (core) aredesirable in a solid state device due to their enhanced photoluminescence and electroluminescence quantum efficienciesand greater tolerance to processing conditions necessary for devicefabrication [2,10 -1213]. QD synthesis in an organic solvent suchas tri-octylphospine or oleylamine results in pasivation of the outerQD surface by these organic molecules. The functional head of theorganic molecules is coordinated with the QD surface, while thelong hydrocarbon-chain tail is associated with the solvent in whichthe QDs are dispersed. This feature of the QDs is what allows themto be dispersed into non-polar solvents, such as hexane, chloroform,or toluene. The organic ligand shell can also be chemicallyexchanged, giving the dots the potential for broad chemical and electronic flexibility (Fig. 2). The combination of broad spectraltunability, chemical flexibility, and solvent processability enable useof nanocrystal QDs as versatile chromophores in organic/inorganichybrid structures such as QD-LEDs.
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