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Nanotechnology Application for Solar Cells: Using Quantum Dots to Modify Absorption Properties

Nanotechnology Application for Solar Cells: Using Quantum Dots to Modify Absorption Properties. QUANTUM NANOS INC. Introduction. How Classical Solar Cells Operate Absorption Coefficient ( α ) Definition and Relevance of α Physical Techniques for Measuring α

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Nanotechnology Application for Solar Cells: Using Quantum Dots to Modify Absorption Properties

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  1. Nanotechnology Application for Solar Cells: Using Quantum Dots to Modify Absorption Properties QUANTUM NANOS INC.

  2. Introduction • How Classical Solar Cells Operate • Absorption Coefficient (α) • Definition and Relevance of α • Physical Techniques for Measuring α • Light Absorption of Quantum Dot Layers • Reasons for Interest Into Quantum Dot Light Absorption • Definition of a Quantum Dot • Formula for Light Absorption of a Quantum Dot • Comparison of α versus Energy for Bulk Material and Quantum Dot • Researchers working on Light Absorption of Quantum Dots • Dr. Sheila Baily • Dr. Ryne Raffaelle • Problem Statement – Determining the most optically absorbent semiconductor material • Problem Solution • Explanation of Theory • Results

  3. How Classical Solar Cells Operate1,2

  4. How Classical Solar Cells Operate1,2

  5. How Classical Solar Cells Operate1,2

  6. How Classical Solar Cells Operate1,2

  7. How Classical Solar Cells Operate1,2

  8. How Classical Solar Cells Operate1,2

  9. How Classical Solar Cells Operate1,2

  10. How Classical Solar Cells Operate1,2

  11. Absorption Coefficient α –Definition and Relevance of α3 • Definition of Absorption Coefficient α • A measure of the rate in decrease of electromagnetic radiation (as light) as it passes through a given substance; the fraction of incident radiant energy absorbed per unit mass or thickness of an absorber.

  12. Absorption Coefficient α –Definition and Relevance of α3 • Unit of Absorption Coefficient α • The units of α are per length (cm-1)

  13. Absorption Coefficient α –Definition and Relevance of α3 • Unit of Absorption Coefficient α • The units of α are per length (cm-1)

  14. Absorption Coefficient α –Definition and Relevance of α4 • Absorption Versus Transmission • Transmission (t): a measure of conduction of radiant energy through a medium, often expressed as a percentage of energy passing through an element or system relative to the amount that entered.

  15. Absorption Coefficient α –Definition and Relevance of α4 • Absorption Versus Transmission • Transmission (t): a measure of conduction of radiant energy through a medium, often expressed as a percentage of energy passing through an element or system relative to the amount that entered.

  16. Absorption Coefficient α –Definition and Relevance of α4 • Absorption Versus Transmission • Transmission (t): a measure of conduction of radiant energy through a medium, often expressed as a percentage of energy passing through an element or system relative to the amount that entered.

  17. Absorption Coefficient α –Physical Techniques for Measuring α5,6 • Optical Transmission Measurement • t – Measured transmission • l – Sample thickness • R - Reflectance

  18. Light Absorption of Quantum Dots – Why We Are Interested7,8,13 • These structures have great potential for optoelectronic applications, one of which may be solar cells • Standard solar cells have a theoretical upper conversion rate of 33%, the theoretical limit on the conversion of sunlight to electricity is 67%

  19. Light Absorption of Quantum Dots – Definition of a Quantum Dot9 Quantum Dot

  20. Light Absorption of Quantum Dots – Definition of a Quantum Dot9 Quantum Dot Layer

  21. Light Absorption of Quantum Dots – Definition of a Quantum Dot9 Quantum Dot Layer

  22. Light Absorption of Quantum Dots – Formula7 • _ • Vav = Average Dot Volume • pfi = 2d momentum matrix element • a = polarization of light • N(ћω) = density of states

  23. Light Absorption of Quantum Dots – Formula12 • Transmission for Quantum dots. • For transmission through n planes of dots, each having the same dot density N and each dot experiencing the same optical field amplitude, the transmission fraction is: • Tn=(1-σN)n ≈ (1-nσN) ; (σN << 1) • σrepresents a cross section of the layer

  24. Light Absorption of Quantum Dots – Comparison of α versus Energy for Bulk Material and Quantum Dot9

  25. Light Absorption of Quantum Dots – Comparison of α versus Energy for Bulk Material and Quantum Dot

  26. Light Absorption of Quantum Dots – Comparison of α versus Energy for Bulk Material and Quantum Dot

  27. Light Absorption of Quantum Dots – Comparison of α versus Energy for Bulk Material and Quantum Dot7

  28. Light Absorption of Quantum Dots – Comparison of α versus Energy for Bulk Material and Quantum Dot7

  29. Researchers Working on Light Absorption of Quantum Dot Layers • Dr. S. Bailey • Using quantum dots in a solar cell to create an intermediate band • IEEE Photovoltaic Specialist Conference (PVSC) Executive Committee since 1987

  30. Researchers Working on Light Absorption of Quantum Dot Layers11 • Dr. Ryne R • RIT • NanoPower Laboratories • Organic and Plastic Solar Cells Combined with Quantum Dot Layers

  31. Problem Solution – Explanation of theory Photon Absorption • z = propagation direction • nr = refractive index • omega = frequency • alpha = absorption coefficient • Laws of Conservation • Energy • Momentum Photon Emission Figures based on Singh textbook

  32. Problem Statement – Determining the most optically absorbent semiconductor bulk • Consider InP and GaAs as being the available semiconductors to create a solar cell. This solar cell will be a hybrid, consisting of a traditional solar cell created with either InP or GaAs, and coating layers of quantum dots of either InP or GaAs. If maximizing absorption is the only criteria for designing the solar cell, which material should be used for the bulk? Which should be used for the quantum dot layers? Assume the density of states for quantum dot layers of both materials is equal and occurs at the same point, E = .1eV, and that the polarization-momentum product sum is the same in both cases.

  33. Problem Statement – Determining the most optically absorbent semiconductor bulk • Absorption coefficient of InP and GaAs • Required constants by material14

  34. Problem Solution – Results: GaAs Bulk

  35. Problem Solution – Results: InP Bulk

  36. Problem Solution – Results

  37. Problem Solution – Results: GaAs Quantum Dot Layer

  38. Problem Solution – Results: InP Quantum Dot Layer

  39. References • Seale, Eric. Solar Cells: Shedding a Little Light on Photovoltaics. 28, Feb. 2002. Solarbotics. <http://www.solarbotics.net/starting/200202_solar_cells/200202_solar_cell_physics.html>. Accessed 03/20/2005. • Pierret, Robert F. Semiconductor Device Fundaments. Addison Wesley Longman, 1996. pp 198-205. • Anonymous. Absorption Coefficient. Undated. LaborLawTalk. <http://dictionary.laborlawtalk.com/absorption_coefficient>. Accessed 04/01/2005. • Anonymous. Transmission (T). Undated. Photonics Directory. <http://www.photonics.com/dictionary/lookup/XQ/ASP/url.lookup/entrynum.5189/letter.t/pu./QX/lookup.htm>. Accessed 04/01/2005. • Augustine, G.  Jokerst, N.M.  Rohatgi, A. Absorption measurements of doped thin film InP for solar cell modeling. IEEE:Indium Phosphide and Related Materials, 1992., Fourth International Conference on. 21-24 April 1992. • Gerber, D.S.   Maracas, G.N.  A simple method for extraction of multiple quantum well absorption coefficient from reflectance and transmittance measurements. Quantum Electronics, IEEE Journal of. Volume: 29 , Issue: 10. Oct. 1993. • Kochman, B; Singh, J; et al. Absorption, Carrier Lifetime, and Gain in InAs-GaAs Quantum Dot Infrared Photodetectors. IEEE Journal of Quantum Electronics. Volume 39, Number 3. March 2003. • Anonymous. Photovoltaics. Evident Technologies. Undated. <http://www.evidenttech.com/applications/quantum-dot-solar-cells.php>. Accessed 04/14/2005. • Singh, J. Modern Physics for Engineers. John Wiley & Sons, Inc. 1999. pp 34, 156. • Wu, Y. Singh, J. Polar Heterostructure for Multifunction Devices: Theoretical Studies. IEEE Transaction on Electron Devices. VOL. 52, NO. 2, FEBRUARY 2005 • Raffaelle, R. Profile of Ryne P. Raffaelle. RIT Department of Physics. Undated. <http://www.rit.edu/~physics/facstaff/profiles/raffaeller.shtml>. Accessed 04/10/2005. • Blood, P. On the Dimensionality of Optical Absorption, Gain, and Recombination in Quantum-Confined Structures. IEEE Journal of Quantum Electronics. Vol. 36, No. 3, March 2000. • D. Pan, E. Towne, and S. Kennerly. Strong normal-incident infrared absorption and photo-current spectra from highly uniform (In,Ga)As/GaAs quantum dot structures. IEEE Electronic Letters. 14th May 1998 Vol. 34 No. 10.

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