Future Generation
Solid-State Energy Conversion
Kyle Montgomery
May 12, 2014
kmontgomery.net
kmontgomery@ucdavis.edu
Department of Electrical & Computer Engineering
@KyleMontgomery0
1
About Me
To 2000
In the beginning…
2004
Bachelor’s
2004-2007
Professional
2008
Master’s
2012
PhD
Present
Research & Lecturer
Intern
2
Influences
Jerry Woodall
Distinguished Professor, UC Davis
NAE Member, National Medal of Technology
Compound Semiconductor Materials & Devices
David Wilt
Tech Lead, Air Force Research Lab, Space Vehicles
Former Lead PV Engineer at NASA
Space Photovoltaics, III-V MOVPE
Mark Lundstrom
Distinguished Professor, Purdue
NAE Member
Electron Transport and Device Modeling
3
Overview
Motivation
• The Energy Dilemma
• Opportunities
Research
• Photovoltaics
• Future Directions
Teaching
• Experience: Purdue & UC Davis
• Future Directions
4
Overview
Motivation
• The Energy Dilemma
• Opportunities
Research
• Photovoltaics
• Future Directions
Teaching
• Experience: Purdue & UC Davis
• Future Directions
5
The Energy Dilemma (1/2)
1. We use too much energy
Total Global Energy
Total Energy by Country
OECD: Organization for Economic Cooperation and Development
EIA, International Energy Outlook 2013
6
The Energy Dilemma (2/2)
2. We waste too much energy
Mostly Waste Heat
Coal (41%)
Conversion Loss (62%)
Natural Gas (25%)
Nuclear (21%)
Renewables (12%)
Residential (12%)
Commercial (12%)
Industrial (9%)
US EIA, Monthly Energy Review (January 2014)
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Opportunity: Solar Resource
Covering US
~20M TWh / yr
2011 US
Electricity
Consumption
4100 TWh
Equiv. Land Area
~2000 km2
½ the size of
Rhode Island
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Wide Bandgap Cells for Multijunctions
Eg > 2 eV
K. Montgomery, PhD Thesis, 2012
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Opportunity: Lighting Efficiency
17%
Percentage of total residential & commercial
electricity used for lighting in US (EIA, 2011)
Incandescent
Halogen
Compact Fluorescent
Linear Fluorescent
High Intensity
Discharge (HID)
Light Emitting Diode
(LED)
Efficacy [lm / W]
US DoE, Solid-State Lighting Technology Fact Sheet, PNNL-SA-94206, March 2013.
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Better Ways for Solid State Lighting
Current Technology:
Low Cost, Decent Quality
Ideal Technology:
High Cost, Superior Quality
NEED:
True Green LED
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Overview
Motivation
• The Energy Dilemma
• Opportunities
Research
• Photovoltaics
• Future Directions
Teaching
• Experience: Purdue & UC Davis
• Future Directions
12
Research Contributions
• Reviving Liquid Phase Epitaxy
• GaP Solar Cells
– 2x improvement in spectral response
• AlGaAs Solar Cells
– Enhanced Luminescence Near Crossover
– Towards Dual Junction Integration on Si
• III-V / II-VI Digital Alloys
• Integration to Novel Energy Conversion
Systems
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Semiconductor Menu
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Liquid Phase Epitaxy – Rotating Chamber
Benefits:
• Perfected Crystal Structure
• Better Stoichiometry
• High Growth Rates
• Economical
Challenges:
• Stable Growth Conditions
• Low Supersaturation
K. Montgomery, PhD Thesis, 2012
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Current Density (mA/cm2)
GaP Solar Cells
Internal QE
Voltage (V)
C. R. Allen, et al., Sol. Energ. Mat. Sol. C., 94, 865 (2010).
Wavelength (nm)
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Gettering in GaP
Liquid
O-
Solid
Ga
Al
Mole Fraction P
P
AlGaP
Al-Ga @ 975°C
K. Montgomery, et. al., JEM, 40, 1457-1460 (2011).
GaP
Substrate
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Gettering Yields Higher Response
Zn-S
Zn-O
Exciton
K. Montgomery, et. al., JEM, 40, 1457-1460 (2011).
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AlGaAs Solar Cells by LPE
X. Zhao et.al, PVSC 40 (2014), K. Montgomery, et. al., EMC (2012)
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Non-Isovalent Alloys
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ZnSe-GaAs Digital Alloy
• Superlattice  Miniband formation
• Potential problem: intermediary
compounds at interfaces
Effective
Band Gap
S. Agarwal, K. H. Montgomery, et. al., Electrochemical and Solid-State Letters, 13, H5 (2010).
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Wide Bandgap Cells for Hybrid PV-PT
• Goal: Maximize solar energy conversion using
PV + Heat
• Benefit: Direct heat absorption allows for storage
Temperature (°C)
System Efficiency (@100x)
K. Montgomery, et. al., PVSC 39 (2013) & Manuscript in Preparation
PV Bandgap (eV)
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Future Directions
Wide Bandgap Solar Cells
• Gettered Devices
• Integrated Nanostructures
• Tandem Integration
Engineered Superstrates
• Hybrid Epitaxy
• III-V on Si
• Polycrystalline III-V
• ZnSe-GaAs Epitaxy
• Growth & Doping
• Heterojunction Devices
Non-Isovalent Semiconductors
23
Overview
Motivation
• The Energy Dilemma
• Opportunities
Research
• Photovoltaics
• Future Directions
Teaching
• Experience: Purdue & UC Davis
• Future Directions
24
Teaching Experience: Purdue
• Teaching Assistant
– 2 semesters: Grad Level Microfabrication
• Lessons Learned
– Textbook Knowledge ≠ Fab Skills
– Laboratory Safety
25
Teaching Experience: UC Davis
• Lecturer
– Undergrad Circuits Analysis
– ~200 students
“…not only does he go on to teach us what we need
to know to get by in circuits, he is a compelling
lecturer, caring person, and above all he is able to
deal with classroom issues with grace.”
• Lessons Learned (& still learning!)
– Minimize loss in translation
– Emphasize fundamentals, Expose details
kmontgomery.net/eng17
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Mentorship: UC Davis
PhD Students
Undergraduates
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Teaching Plans: Graduate
• Materials Science for Microsystems
Engineering
• Microelectronics I
• Proposed Course
Solid-State Energy Conversion Materials & Devices
REVIEW: Solid-State Physics,
Material Properties,
Thermodynamics
Photovoltaics
Light Emitting
Thermoelectrics Piezoelectrics
Diodes
“Direct Energy Conversion”
by Angrist (w/supplements)
Emphasis on
Recent
Research
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Teaching Plans: Undergraduate
•
•
•
•
Circuits I-II
(Adv.) Semiconductor Devices
MATLAB Programming
Clean and Renewable Energy Systems
and Sources
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Overview
Motivation
• The Energy Dilemma
• Opportunities
Research
• Photovoltaics
• Future Directions
Teaching
• Experience: Purdue & UC Davis
• Future Directions
30
Acknowledgements
Purdue University
Prof. Mark Lundstrom, ECE
Prof. David Janes, ECE
Prof. Peide Ye, ECE
Prof. Eric Kvam, MSE
Prof. Peter Bermel, ECE
Prof. Gerhard Klimeck, ECE
Prof. Anant Ramdas, Physics
Dionisis Berdebes, ECE
Dr. Jayprakash Bhosale, Physics
Yale University
Prof. Minjoo Larry Lee, EE
UC Davis
Prof. Jerry Woodall, ECE
Prof. Saif Islam, ECE
Prof. Subhash Mahajan, CHMS
Xin Zhao, ECE
UCLA
Dr. Paul Simmonds
Air Force Research Laboratory
David Wilt
Dr. Alex Howard
John Merrill
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Thank you!
Any questions?
kmontgomery.net
kmontgomery@ucdavis.edu
Department of Electrical & Computer Engineering
@KyleMontgomery0
32
Supplemental
kmontgomery.net
kmontgomery@ucdavis.edu
Department of Electrical & Computer Engineering
@KyleMontgomery0
33
ZnSe-GaAs Physical Alloy
• Miscibility previously
demonstrated
• N-type conductivity
generally found
• Lack of prior work due
to difficulty in suitable
deposition technique
W. M. Yim, JAP, 40, 2617–2623, 1969.
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SiC Solar Cells
150 suns
R. P. Raffaelle et. al., 28th PVSC, 2000, pp. 1257–1260.
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AlGaAs Growth by LPE
K. Montgomery, et. al., EMC (2012)
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InGaN Solar Cells
Full Spectrum Coverage
Phase separation
InGaN (37% In)
Defects
InGaN (16.8% In,
2.67 eV)
Jampana, et al., Electron Devic. Lett., 31, 32 (2010).
R. Singh and D. Doppalapudi, Appl. Phys. Lett., 70, 1089 (1997).
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2.19 eV GaInP w/GaAsP
Buffers on GaP
In0.26Ga0.74P
S. Tomasulo, et. al., PVSC 39, 2013.
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Wide Bandgap Cells for High-T
AM0 (FF = 0.80, Pin = 1366.1 W/cm2)
27°C
Efficiency
20
10
900°C
Temperatures up to 450°C
1.0
2.0
3.0
Bandgap
G. A. Landis, et. al., “High-Temperature Solar Cell Development,” NASA, 2004.
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Engineered Superstrates
• Superstrate: Substrate templated with a
heterogeneous material
• III-V on Si
– Needs thick buffer layers
– Problem: Dislocation densities
• LPE may help (w/MOCVD)
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Current Density [mA/cm2]
14
12
10
Al0.23Ga0.77As
(Eg ~ 1.75 eV)
8
Voc = 771 mV
Jsc = 13.8 mA/cm2
FF = 63.4%
Efficiency = 6.8%
6
4
2
0
0
0.2
0.4
0.6
0.8
Voltage [V]
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Primary Photovoltaic Technologies
Low Cost, Low Efficiency
η ~ 6-22%
First Solar
High Cost, High Efficiency
η ~ 28-39% (at xx suns)
SolFocus
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