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Quantum Dot White LEDs

Quantum Dot White LEDs. Jennifer Asis EECS 277A. 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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Quantum Dot White LEDs

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  1. Quantum Dot White LEDs Jennifer Asis EECS 277A

  2. 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

  3. 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/images/OLED_2.JPG

  4. 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/Barriers%20and%20wells.pdf

  5. 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/images/OLED_2.JPG

  6. 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

  7. WLED from Ternary Nanocrystal Composites 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) Advanced Materials (2006) 18 2545-2548

  8. Cathode Electron transport layer Hole blocking layer Quantum dot layer Hole transport layer Hole injection layer Anode RGB Colloidal Quantum Dot Monolayer Red: CdSe/ZnS (λ=620 nm) Green: ZnSe/CdSe (λ=540 nm) Blue: ZnCdS (λ=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

  9. Summary Size-dependent properties of Quantum Dots LEDs – PN Diode

  10. 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

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