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Plasmonic Applications for Thin Film PV




                 A Superior Broadband Light Trapping Technology

Matter, Inc. ...
Commercial Considerations



         Our technology provides substantial efficiency enhancements and performance improvem...
Commercial Considerations


         Commercial grade sputtering equipment was used to deposit controlled structures and c...
An Obvious Need for Photon Management in Thin Film PV



            A large mismatch exists between electronic and photon...
Plasmonics Enables Unparalleled Light Concentrating



          Light focusing by a 20nm Aluminum particle




          ...
Plasmonic Structures are Robust and Scalable




                                             
 Plasmonic structures and ...
Plasmonics Offers Simultaneous Electrical & Optical Functions


        •    Metal dielectric interfaces support
         ...
Conventional Light Trapping Schemes
                         Utilizing Wavelength Scale Texturing to Boost Absorption
    ...
Nanoscale particles are highly effective for light
                      scattering and trapping “without” absorption




...
Utilizing Sub-Wavelength Metallic Nanostructures
                                Example from Halas Group (Rice University...
Utilizing Sub-Wavelength Metallic Nanostructures
                                 Example from Yu Group (UC San Diego)



...
Rational Design of a Plasmon Enhanced AR Coating
                  Simulations to optimize absorption in Si and Jsc




  ...
Example of a Plasmon Enhanced Thin Film Solar Cell
                 Goal: Quantify and Optimize Absorption Enhancement in ...
Full-field Simulations Showing Different Coupling Regimes
                        Periodic array of Ag nano-stripes on top ...
Absorption Enhancements in an E- βPlot
                             Absorption due to waveguide and particle resonances
  ...
Optimization of TE and TM Absorption Enhancements
            Optimizing absorption for randomly polarized sunlight w/equa...
Spectral Contributions to Total Short Circuit Current


                                       I(λ) is the solar spectral ...
Total Short Circuit Current Enhancement
                                Calculated from Spectral Contributions




       ...
Spectral Contributions to Plasmon Enhanced Photocurrent
                      Strong enhancements from light trapping and ...
Design, Fabrication and Optimization Strategy




          •    Initial Computational Design

          •    Deposition o...
Computational Design & Optimization




            •    State of the art full-field simulations (FDTD and FDFD)

         ...
Coating of Solar Cells




      •    Coatings perform excellent passivation

      •    Coatings enable light concentrati...
Structural and Optical Studies




            •    Structure: SEM, RBS, and AFM

            •    Optical: Reflection and ...
Simulation Optical Data Using Structural Information

     •    Experimental data can be understood with simulations


   ...
Performance Verification




      •    Verify that enhancement meets required performance criteria

      •    Continue to...
Cell Fabrication and Testing




                                 Flexible Solar Collector Courtesy of Global Solar




Ma...
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  1. 1. Plasmonic Applications for Thin Film PV A Superior Broadband Light Trapping Technology Matter, Inc. © 2008 Confidential
  2. 2. Commercial Considerations Our technology provides substantial efficiency enhancements and performance improvements in thin film solar cells. First order optimization results demonstrate close to 50% increase in short circuit current based on an ideal thin cell operating at 100% electrical efficiency. Optimization and development can substantially improve performance. Results were derived from testing actual depositions and generating simulations based on experimental data. First order metallic nanostructures were deposited on an independent substrate interface using a sample silicon wafer characterized as 100 mm P<100> 381±15µm, 5-8.5 Ω-cm SSP with 20 nm thermal oxide. Matter, Inc. © 2008 Confidential
  3. 3. Commercial Considerations Commercial grade sputtering equipment was used to deposit controlled structures and coatings. Full- field electromagnetic simulations accurately predict the performance of metallic nano particle coatings. We have an ongoing development cycle for optimization and fabrication of operating prototype thin film cells. These will be expressed in a-Si-ITO with optimized designed thickness of 2-500 nm. They may be significantly thinner than commercial models allowing substantial material cost savings. Integration in the fabrication process could incorporate our coatings in a modified ITO deposition stage. Since our technology is essentially substrate independent it can be designed and optimized for Cigs / CdTe or any other thin film cell. Matter, Inc. © 2008 Confidential
  4. 4. An Obvious Need for Photon Management in Thin Film PV A large mismatch exists between electronic and photonic lengthscales  Thick cells are desirable from a photonics standpoint to enable efficient light absorption  Thin cells are desirable from an electronics standpoint to enable efficient charge extraction A radical new technology is required to match both length scales… …and to break open the barriers towards substantially higher efficiencies The rapidly developing field of Plasmonics offers the right ingredients for this task Matter, Inc. © 2008 Confidential
  5. 5. Plasmonics Enables Unparalleled Light Concentrating Light focusing by a 20nm Aluminum particle  Plasmonics enables unparalleled light concentration and light trapping capabilities C.F. Bohren, D.R. Huffman, Absorption and Scattering of Light by Small Particles, Wiley, New York. 1983. Explanation: Electron oscillations/plasmonics  Plasmonics allows for simultaneous electrical and optical functions (light and charge management) Matter, Inc. © 2008 Confidential
  6. 6. Plasmonic Structures are Robust and Scalable  Plasmonic structures and coatings are robust in harsh environments  Plasmonic structures can be generated using inexpensive, scalable deposition techniques Matter, Inc. © 2008 Confidential
  7. 7. Plasmonics Offers Simultaneous Electrical & Optical Functions • Metal dielectric interfaces support surface plasmons (“light”) • Metals exhibit high electrical conductivities Metals enable simultaneous charge extraction and light concentration / trapping Rashid Zia, Jon A. Schuller and Mark L. Brongersma, Materials Today 9, 20-27 (2006). Matter, Inc. © 2008 Confidential
  8. 8. Conventional Light Trapping Schemes Utilizing Wavelength Scale Texturing to Boost Absorption Examples from Martin Green Group (UNSW, Australia) • Efficiencies > 20% have been realized • Careful surface passivation is required • Increased optical absorption • Not ideal for thin film cells Matter, Inc. © 2008 Confidential
  9. 9. Nanoscale particles are highly effective for light scattering and trapping “without” absorption Efficiencies, Q, are normalized cross sections: Matter, Inc. © 2008 Confidential
  10. 10. Utilizing Sub-Wavelength Metallic Nanostructures Example from Halas Group (Rice University) Measurement of local photocurrent change due to particles: • Bright spots indicate current enhancement and dark spots indicate a reduction • Photocurrent is increased at some wavelengths and reduced at others • It is possible to attain a boost in the overall energy conversion efficiency Matter, Inc. © 2008 Confidential
  11. 11. Utilizing Sub-Wavelength Metallic Nanostructures Example from Yu Group (UC San Diego) • Results are very encouraging • Simulations do not include entire structure (just particle response) • Measurement not with a Solar Simulator (halogen bulb) • We can further optimize and scale this technology to large areas Matter, Inc. © 2008 Confidential
  12. 12. Rational Design of a Plasmon Enhanced AR Coating Simulations to optimize absorption in Si and Jsc Jsc = Generated short circuit current density I(λ) = Spectral irradiance Where: IQE(λ) = Internal quantum efficiency T(λ) = Transmission coefficient • Often the product of IQE(λ) and T(λ) is stated as spectral response: SR(λ) Where: SR(λ) = JPh(λ) / I(λ) = photocurrent generated at λ/spectral irradiance • In initial simulations we have assumed perfect electrical quality (IQE = 100%) Matter, Inc. © 2008 Confidential
  13. 13. Example of a Plasmon Enhanced Thin Film Solar Cell Goal: Quantify and Optimize Absorption Enhancement in a thin Si layer • Incident light is assumed to be randomly polarized (equal TM and TE contributions) • Metal stripes enhance absorption by a) Coupling to waveguide modes of Si slab; b) Exploiting plasmonic resonances of metal stripes • Both effects can operate in unison • Metal stripes can assist in the current extraction as well • Metals are separated from the Si layer, enabling good passivation Matter, Inc. © 2008 Confidential
  14. 14. Full-field Simulations Showing Different Coupling Regimes Periodic array of Ag nano-stripes on top of a 50 nm Si slab • Illustration of both types of couplings for TM polarization • Plots show normalized absorption enhancement (80 nm wide x 60 nm thick particles) • Resonances can be engineered for maximum enhancement Matter, Inc. © 2008 Confidential
  15. 15. Absorption Enhancements in an E- βPlot Absorption due to waveguide and particle resonances Plot of absorption enhancement with and without 60 x 80 nm particles on 10 nm oxide • Enhancement is on a 10 Log scale: Red and Yellow areas provide strong enhancement Blue area corresponds to absorption reduction • Highest absorption enhancement occurs for relatively small β (periods around 315 nm) Matter, Inc. © 2008 Confidential
  16. 16. Optimization of TE and TM Absorption Enhancements Optimizing absorption for randomly polarized sunlight w/equal TM & TE contributions Plots of absorption enhancement with and without 60 x 80 nm particles on 10 nm oxide TM Enhancement Map TE Enhancement Map • Enhancement is on a 10 Log scale: Red and Yellow areas provide strong enhancement Blue area corresponds to absorption reduction • Highest absorption enhancement occurs for relatively small β (periods around 315 nm) Matter, Inc. © 2008 Confidential
  17. 17. Spectral Contributions to Total Short Circuit Current I(λ) is the solar spectral irradiance SRBare(λ) is the spectral response of the bare Si slab without metallic nanoparticles Π(λ) is the absorption enhancement provided by the metal as calculated in the previous slide Matter, Inc. © 2008 Confidential
  18. 18. Total Short Circuit Current Enhancement Calculated from Spectral Contributions • Enhancements of approximately 45% are obtainable in a first optimization round • Higher enhancements can be obtained with an optimized development Matter, Inc. © 2008 Confidential
  19. 19. Spectral Contributions to Plasmon Enhanced Photocurrent Strong enhancements from light trapping and particle resonances • Short circuit current vs. wavelength for bare Si slab with and without metallic structures Matter, Inc. © 2008 Confidential
  20. 20. Design, Fabrication and Optimization Strategy • Initial Computational Design • Deposition on Cells • Structural and Optical Studies Optimization Loop • Revised Optical Simulations • Performance Verification • Cell Fabrication and Test Matter, Inc. © 2008 Confidential
  21. 21. Computational Design & Optimization • State of the art full-field simulations (FDTD and FDFD) • Coatings designed for specific thin film cells • Any semiconductor material/PV cell can be modeled Matter, Inc. © 2008 Confidential
  22. 22. Coating of Solar Cells • Coatings perform excellent passivation • Coatings enable light concentration and trapping • Scalable deposition technology Matter, Inc. © 2008 Confidential
  23. 23. Structural and Optical Studies • Structure: SEM, RBS, and AFM • Optical: Reflection and elipsometry • Parameters are extracted: particle size, spacing, shape, metal volume Matter, Inc. © 2008 Confidential
  24. 24. Simulation Optical Data Using Structural Information • Experimental data can be understood with simulations Example: Coating with 32 nm average diameter particles • Simulations provide: reflection, transmission, and absorption data • Simulations provide suggestions for optimizing particle size, shape, spacing,etc. Matter, Inc. © 2008 Confidential
  25. 25. Performance Verification • Verify that enhancement meets required performance criteria • Continue to refine design process with new data Matter, Inc. © 2008 Confidential
  26. 26. Cell Fabrication and Testing Flexible Solar Collector Courtesy of Global Solar Matter, Inc. © 2008 Confidential

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