Quantum Dot White LEDs Jennifer Asis EECS 277A. Motivation Science 2008 319 1776 Energy efficient...
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![Page 1: Quantum Dot White LEDs Jennifer Asis EECS 277A. Motivation Science 2008 319 1776 Energy efficient Long life Durable Small size Design flexibility.](https://reader034.fdocuments.in/reader034/viewer/2022051401/56649d9d5503460f94a86908/html5/thumbnails/1.jpg)
Quantum Dot White LEDs
Jennifer Asis
EECS 277A
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Motivation
www.reprap.org Science 2008 319 1776
•Energy efficient•Long life
•Durable
•Small size
•Design flexibility
Replacement for incandescent and fluorescent lighting
Improve White LED performance
Quantum dot white LED
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White LEDS• Multichip devices
(red-,green-,blue-emitting chips)
• Single-chip devices (phosphors)
http://www.meisemi.com/image/CIE.gif
• Electroluminescence (EL)– Light emitted in response to
an electric current– Result of radiative
recombination
(Charge injection)– Photon is released
http://www.science24.com/resources/paper/15507/images/OLED_2.JPG
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Quantum Dots
http://chem.ps.uci.edu/~lawm/Barriers%20and%20wells.pdf
• Colloidal inorganic semiconductor nanocrystal– II-VI semiconductor
materials (i.e. CdS, CdSe)
• 2-10 nm in diameter– Exhibit strongly size-
dependent optical and electrical properties
– Quantum confinement effects
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Quantum Confinement
• Light-Emitting Diode (LED) is a PN junction– Recombination of an
electron and hole– Electron-hole pair known
as an exciton
e- h+
• Size of semiconductor crystal on the order of Exciton Bohr Radius– Discrete energy levels
→Tunable band gap
Exciton Bohr Radius
http://www.science24.com/resources/paper/15507/images/OLED_2.JPG
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InGaN-CdSe-ZnSe Quantum Dot White LEDs
InGaN CdSe-ZnSe
IEEE Photonics Technology Letters 2006 18 [1] 193
• Single-chip InGaN used as excitation source
• CdSe-ZnSe QDs used as phosphor
• Efficiency 7.2 lm/W at 20 mA– Commercial WLEDs (15-
30 lm/W)
• CIE (0.33, 0.33)• CRI = 91
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WLED from Ternary Nanocrystal Composites
Advanced Materials (2006) 18 2545-2548
Charge transfer mechanisms:-Charge trapping-Forster energy transfer
QDs: CdSe/ZnS-Red λ =618 nm-Green λ =540 nm-Blue λ =490 nm
At 13 V: CIE (0.32, 0.45)
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RGB Colloidal Quantum Dot Monolayer
Nano Letters (2007) 7 [8] 2196-2200
Electron transport layer
Cathode
Hole blocking layerQuantum dot layer
Hole transport layer
Hole injection layerAnode
Red: CdSe/ZnS (λ=620 nm)Green: ZnSe/CdSe (λ=540 nm)Blue: ZnCdS (λ=440 nm)
Charge injection into blue QDs more efficient at higher applied biases
At 9V:CIE (0.35, 0.41)CRI = 86Brightness: 92 cd/m2
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Summary
Size-dependent properties of Quantum Dots
LEDs – PN Diode
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References• X. Zhao, “Commercialization of Quantum Dot White Light Emitting Diode
Technology,” M.Eng. Thesis (2006).• A.P. Alivisatos, “Semiconductor Clusters, Nanocrystals, and Quantum Dots,” Science,
271 [5251], 933-937 (1996).• Y. Li, A. Rizzo, R. Cingolani, and G.Gigli, “White-light-emitting diodes using
semiconductor nanocrystals,” Microchim Acta, 159, 207-215 (2007).• H.S. Chen, C.K. Hsu, and H.Y. Hong, “InGaN-CdSe-ZnSe Quantum Dots White
LEDs,” IEEE Photonics Technology Letters, 18 [1], 193-195 (2006).• Y.Li, A. Rizzo, R. Cingolani, and G. Gigli, “Bright White-Light-Emitting Device from
Ternary Nanocrystal Composites,” Advanced Materials, 18 2545-2548 (2006).• P.O. Anikeeva, J.E. Halpert, M.G. Bawendi, and V. Bulovi, “Electroluminescence from
a Mixed Red-Green-Blue Colloidal Quantum Dot Monolayer,” Nano Letters, 7 [8] 2196-2200 (2007).
• http://www.evidenttech.com