Quantum Dot White LEDs

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Quantum Dot White LEDs

• Jennifer Asis
• EECS 277A

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Motivation

• Energy
• efficient

• Small size

• Long life

• Design
• flexibility

• Durable

Replacement for incandescent and fluorescent
lighting
Improve White LED performance
Quantum dot white LED
www.reprap.org Science 2008 319 1776
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White LEDS

• Multichip devices (red-,green-,blue-emitting
  chips)
• Single-chip devices (phosphors)

• Electroluminescence (EL)
• Light emitted in response to an electric current
• Result of radiative recombination
• (Charge injection)
• Photon is released

http//www.meisemi.com/image/CIE.gif
http//www.science24.com/resources/paper/15507/ima
ges/OLED_2.JPG
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Quantum Dots

• 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

http//chem.ps.uci.edu/lawm/Barriers20and20well
s.pdf
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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

• Size of semiconductor crystal on the order of
  Exciton Bohr Radius
• Discrete energy levels
• ?Tunable band gap

e-
h
Exciton Bohr Radius
http//www.science24.com/resources/paper/15507/ima
ges/OLED_2.JPG
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InGaN-CdSe-ZnSe Quantum Dot White LEDs

• Single-chip InGaN used as excitation source
• CdSe-ZnSe QDs used as phosphor

InGaN
CdSe-ZnSe

• Efficiency 7.2 lm/W at 20 mA
• Commercial WLEDs (15-30 lm/W)
• CIE (0.33, 0.33)
• CRI 91

IEEE Photonics Technology Letters 2006 18 1 193
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WLED from Ternary Nanocrystal Composites
Charge transfer mechanisms -Charge
trapping -Forster energy transfer
QDs CdSe/ZnS -Red ? 618 nm -Green ? 540
nm -Blue ? 490 nm
At 13 V CIE (0.32, 0.45)
Advanced Materials (2006) 18 2545-2548
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RGB Colloidal Quantum Dot Monolayer
Red CdSe/ZnS (?620 nm) Green ZnSe/CdSe (?540
nm) Blue ZnCdS (?440 nm)
At 9V CIE (0.35, 0.41) CRI 86 Brightness 92
cd/m2
Charge injection into blue QDs more efficient at
higher applied biases
Nano Letters (2007) 7 8 2196-2200
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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