Quantum Dot Spectrum Converter Coverglass for Enhanced High Efficiency Photovoltaics Theodore G. Stern DR Technologies, Inc. San Diego, CA 92020 Business Area Manager Space Power, Optical and Thermal Products AIAA Associate Fellow 1
Acknowledgments This work was sponsored in part by the NASA Glenn Research Center under SBIRs NNC06CA64C & 69C The author would also like to thank Sheila Bailey, Barry Hillard and Mike Piszczor of the NASA Glenn Research Center, Stephanie Castro of the Ohio Aerospace Institute, and Margaret Hines of Evident Technologies for their technical guidance and support 2
Quantum Dots and Fluorescence Quantum Dots are Nano-Sized Semiconductors Inherent Fluorescence Property QD Sizes Determines Spectral Characteristics Florescence Emission Wavelength Peak (λe @ Eg) Absorbance First Exciton Band as Well As Blue-UV Absorption Arbitrary Units Absorbance 4 3 2 1 0 QD Absorbance and Emission 250 450 650 850 Wavelength (nm) 3
Multiple Exciton Generation (MEG) Phenomenon Observed for Photons Energy > 2*Eg-qd Quantum Yields > 250% Have Been Measured One UV Photon Yields 2-3 Red Photons Can Sidestep Inherent Photovoltaic Limitations of Single Quantum Process Blue Loss 4
QDSC Coverglass QDSC Cover Converts Otherwise Unused UV and Poorly Used Blue Photons MEG Effects Can Allow Higher Electron-Hole Generation Yield Molded Silicone Sheet Provides Integral Cell Cover and Assembly Self-Tooling 5
QDSC PV Subsystem Model Accounts For Photon Chain With Spectral Conversion and MEG Numerical Analysis / Monte Carlo Methodology Spline Curve Matching Tracks to Established Test Data Solar Spectrum Reflection and Absorption Loss Transmission and/or Concentration Q-Dots Parameters: Species Size Coating Medium Extinction Coefficient Transmission to Cell Cell Response Si GaAs DJ, TJ Current Collection Panel Losses Packing Factor Wiring, Harness Loss Diode Loss 6
Solar Spectrum Modeled from 200 4800nm in 10nm Bands Existing Measured AM0 Spectral Data W/cm2/nm 2.5 2 1.5 1 0.5 0 Solar Spectrum 0 1000 2000 3000 Wavelength (nm) 7
Quantum Dot Florescence Spectra Need Both Good Absorption Spectrum and Emission Data First Exciton Wavelength Emission Wavelength (Stokes) Separation and Overlap is Key Quantum Dots Provide Wide Spectral Choice Commercial QD s Selected For Initial Tests 8
Modeled Quantum Dot Spectrum Spline and Gaussian Model of Test Data Absorbance 5.000 4.500 4.000 QDSC Absorbance and Emission 3.500 3.000 2.500 2.000 1.50 0 1.000 0.500-0 100 200 300 400 500 600 700 800 900 1000 Wavelength (nm) 9
Solar Cell Response Fall Off of Blue Response Typical for Long- Wavelength Eg Single Bandgap Cells Result of UV Filtering, AR Coating and Inherent Blue Response 1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 300 400 500 600 700 800 900 1000 1100-0.1 10
Solar Cell Illumination QDSC Cover filters Blue and UV Florescence Adds Significant near-ir Illumination m mw/cm2/nm * 3.00 2.50 2.00 1.50 1.00 0.50 - Spectrum Input To Solar Cell from Direct Solar Transmittance together with QD Fluorescent Emission So 250 350 450 550 650 750 850 950 Wavelength (nm) 11
Parametric Study Input Measured Data From COTS Quantum Dots Measured Data From COTS Photovoltaic Solar Cells Parametric Variables Quantum Efficiency / Quantum Yield QD Characteristic Emission Wavelength QD Absorbance MEG On/Off Solar Cell Type Si GaAs AlGaAsP α-si CIGS Cell Efficiency 0.2 0.198 0.196 0.194 0.192 0.19 0.188 PV Efficiency as a function of Absorbance and Emission Wavelength for SJ GaAs Crystalline Cell and PbS 400.00 500.00 600.00 700.00 800.00 900.00 Emission Wavelength (nm) QE = 95% in all cases Absorbance - 0.050 0.100 0.150 0.200 0.250 0.300 0.350 0.400 0.450 0.500 0.550 0.600 0.650 0.700 0.750 0.800 0.850 12
Results of QDSC-Cover Parametric Analysis Current Enhancements For All Solar Cell Types Most Significant Gains for Single Junction, Low Cost Devices Good Ole Silicon and Thin Film CIGS With MEG Characteristic Wavelengths (nm) Current Solar Cell Bandgap QD Type QD Emission First Absorption Pk Enhancement Silicon 1.12 PbS 800 650 10.0% GaAs 1.42 PbS 800 650 6.0% GaAs 1.42 CdTe-CdS 500 490 6.0% InGaAsP 1.8 CdTe-CdS 500 490 7.5% CIGS 1.08 CdTe-CdS 550 540 8.5% a-si 2.76 CdTe-CdS 440 430 2.3% 13
Low Cost Modular QDSC Solar Array Lamination Approach for Solar Panels Solar Cell Cover/Shield, Interconnect, Stringing, Laydown, Wiring, Insulation, Composite Facesheet/Core/Facesheet All Laminated, Mechanically and Electrically Bonded IN ONE STEP!!! 14
Quantum Dot Luminescent Concentrator Light Trapping by Total Internal Reflection Concentrator Benefits Without Tracking Requirement Efficiency 7.0% 6.0% 5.0% 4.0% 3.0% 2.0% 1.0% Concentrator Efficiency w/meg GaAs Cell - PbS Quantum Dot 0.0% 400 600 800 1000 1200 QD Emission Wavelength (nm) Absorbance (au) 0.2 0.4 0.6 0.8 1 15
Thin Film Photovoltaics Enhancement QDSC Allows Higher Efficiency TFPV Reasonable Array and Structure Sizes Could Enable TFPV as a Low Cost Alternative Courtesy Composite Technology Development, Inc. 16
Conclusions A Quantum Dot Spectrum Converter Can Enhance the Output of Single Bandgap Low-Cost Solar Cells Implementation in an Integral Cover Allows a Low- Cost Single Step Lamination Process for Solar Arrays The Ultimate Goal of Affordable Power In Space Is Achievable With Advanced Technology 17