Emerging High-Efficiency Low-Cost Solar Cell Technologies
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Transcript of Emerging High-Efficiency Low-Cost Solar Cell Technologies
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Emerging High-Efficiency Low-Cost Solar Cell Technologies
Mike McGehee
Materials Science and Engineering Center for Advanced Molecular Photovoltaics
Bay Area Photovoltaic Consortium Precourt Institute for Energy
Stanford University
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Source: US DOE report “$1/W Photovoltaic Systems,” August 2010.
DOE’s Sunshot Goal: $1/W by 2017
A module efficiency of 25 % is wanted to enable the installation cost reductions.
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Last Week’s Lecture by Anshu Sahoo and Stefan Reichelstein
In 2017 the cost of silicon cells will probably be $0.65/W.
Silicon is currently competitive in favorable locations with the current subsidies.
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National Renewable Energy Laboratory Innovation for Our Energy Future
There are many approaches to making PV cells and experts do not agree on which one is the best
20x-100x 500x Cu(In,Ga)Se2 ~ 1-2 um c-Si ~ 180 um
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Efficiency Records Chart available at: h6p://www.nrel.gov/ncpv/images/efficiency_chart.jpg. The chart above was downloaded on 2/27/2014.
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National Renewable Energy Laboratory Innovation for Our Energy Future
Silicon PV
Silicon Feedstock Ingot Growth Slicing Wafers
Cell Fabrication Module Encapsulation Photovoltaic System
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National Renewable Energy Laboratory Innovation for Our Energy Future
19.6% efficient planar cells on silicon
Source: J-H Lai, IEEE PVSC, June 2011
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Cost analysis of Si Modules
8 Tonio Buonassisi et al., Energy and Env. Sci. 5 (2012) p. 5874.
LOS is line of sight
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9 Tonio Buonassisi et al., Energy and Env. Sci. 5 (2012) p. 5874.
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10 Tonio Buonassisi et al., Energy and Env. Sci. 5 (2012) p. 5874.
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Cost analysis of Si Modules
11 Tonio Buonassisi et al., Energy and Env. Sci. 5 (2012) p. 5874.
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Thin Crystalline Silicon Cells
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Using nanocones to enable complete light absorp2on in thin Si
Sangmoo Jeung, Mike McGehee, Yi Cui, Nature Comm. in press.
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Gallium Arsenide • The 1.4 eV band gap is ideal for solar cells. • High quality films are grown on single crystal substrates with MOCVD.
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Photon recycling
Eli Yablonovitch et al., IEEE J. of Photovoltaics, 2 (2012) p. 303.
Si GaAs
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Why thin film GaAs is beGer
• RemiGed photons are weakly absorbed and can easily travel more than a carrier diffusion length away from the junc2on in a wafer-‐based device.
• In a thin cell, a mirror keeps photons near the pn junc2on.
Eli Yablonovitch et al., IEEE J. of Photovoltaics, 2 (2012) p. 303.
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Theore2cal limits
Eli Yablonovitch et al., IEEE J. of Photovoltaics, 2 (2012) p. 303.
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NREL is a na2onal laboratory of the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, operated by the Alliance for Sustainable Energy, LLC.
A Manufacturing Cost Analysis Relevant to Photovoltaic Cells Fabricated with III-‐Vs
The Na5onal Center for Photovoltaics Aaron Ptak David Young ScoG Ward Myles Steiner Pauls Stradins John Geisz Daniel Friedman Sarah Kurtz
Graphics and Communica5ons Alfred Hicks Kendra Palmer Nicole Harrison
Strategic Energy Analysis Center Ted L. James David Feldman Robert Margolis
Hydrogen Technologies Center (Photoelectrolysis Interest) Todd Deutsch Henning Doscher John Turner
September 30, 2013 Publica2on Number: NREL/PR-‐6A20-‐60126 Contract Number: NREL: DE-‐AC36-‐08GO28308
Michael Woodhouse Alan Goodrich AddiVonal NREL Contributors:
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An Example Process Flow for Making Single-Junction III-V Devices by ELO
Ongoing NREL Analysis 9/13/2013
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Reference Case Repolishing Cost
(Assuming a Repolish is Needed for Each Growth Cycle)
NREL Cost Analysis 9/13/2013
Step 1: Unpack and Clean GaAs Parent Epi-Substrate—3 (The Reference Case Scenario in the Bar Chart Assumes 50 Reuses and 70% Yields)
$0.0
$1.0
$2.0
$3.0
$4.0
$5.0
$6.0
$7.0
Cur
rent
US
$/ W
p (D
C)
Cost Estimates for Unpacking Parent EpiSubstrate 500 MWp(DC) U. S. Facility, 25% Cell Efficiency and 70% Yield
Depreciation (Equipment and Building)
Utilities
Labor & Maintenance
Chemical Surface Treatment Materials
Epi-Wafer (50 reuses)
Chemical Mechanical Polishing (CMP)
NREL DRAFT Cost Analysis 9/13/2013
Please see the annotated notes below this slide for more details.
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Cost Summary, by Step, for the Reference Case. (20 substrate reusages, precursor uVlizaVons of 30% for the III-‐ source and 20% for the V-‐ source, 15 µm/hr GaAs, 70% effecVve cell yield )
$0.00
$1.00
$2.00
$3.00
$4.00
$5.00
$6.00
$7.00
Unpack and Clean
Epiwafer
MOVPE of AlAs Release
Layer
MOVPE of GaAs Front
Contact Layer
MOVPE of AlInGaP Window
Layer
MOVPE of GaAs Emitter
MOVPE of GaAs Base
MOVPE of InGaP Back
Surface Field
MOVPE of AlGaAs
Buffer/ Back Contact Layer
Bottom Metallization
Dissolve AlAs Release
Layer & Epitaxial Lift-
Off
Etching of GaAs
Contact Layer and
ARC
Top Metallization
Edge Isolation,
Test and Sort
Cur
rent
US
$/ W
p(D
C)
Calculated Device Processing Costs for Single-Junction III-V's 500 MWP(DC) U.S. Facility, 25% Cell Efficiency, 70% Yield, 5 yrs Equipment Depreciation
Depreciation Costs (Equipment and Building)
Utility Costs
Labor & Maintenance Costs
Material Costs
NREL Cost Analysis. 9/13/2013
TACT time in base layer step
20 Reuses Includes CMP
2.5 µm, 15 µm/hr 8 substrates per reactor
25 nm Au
50 nm, 4 µm/hr
100 nm 3 µm/hr
Please see the annotated notes below this slide for more details.
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Technology Roadmap SimulaVons for Single-‐JuncVon III-‐V’s (GaAs Base)
$0.00
$1.00
$2.00
$3.00
$4.00
$5.00
$6.00
$7.00
$8.00
$9.00
$10.00
$11.00
$12.00
$13.00
Cur
rent
US
$/ W
p(D
C)
Reference Case (!=25%) Mid-Term (!=27%) Long-Term MOVPE (!=29%) Long-Term SJ GaAs (!=29%)
Cost Model Results for Single-Junction (SJ) GaAs Solar Cells by ELO $150 for 133 cm2 Substrates, 0.25 Laborers per Reactor, U.S. Manufacturing
All stated efficiencies are AM 1.5G and 1000 W/m2 Required margin to meet minimum sustainable cell price Depreciation (Capital Equipment and Building) Electricity
Labor & Maintenance
Materials Costs for Device Layers
Parent epi-substrate and Chemical-Mechanical Polishing
$4.60/ W
Improvements in Epi-Substrate Utilization Increase Parent Epi-Substrate Reuses: From 20 reuses to 500 reuses Replace Chemical-Mechanical Repolishing with Wet Bench Surface Preparation Lower WACC: From 9% to 7%
$13.60/ W
!!$0.50/ W (SunShot Adjusted Cell Price Goal)
Novel Manufacturing Process* *Publicly Available Demonstrations Currently Unknown Reduce Device Materials Costs by 80% from the Long-Term Case for MOVPE (e.g., different precursors and higher utilizations) Reduce Cell Labor & Depreciation Expenses by 80% from the Long-Term Case for MOVPE (e.g.,, higher dep. rates and larger batch sizes)
NREL Cost Analysis 9/23/2013
Improvements in Cell Processing Increase Material Utilization: From 30% to 50% for TMG, TMI, and TMA From 20% to 30% for AsH3 and PH3 Reduce GaAs Base Thickness: From 2.5 µm to 1.5 µm Increase GaAs Deposition Rate: From 15 µm/hr to 20 µm/hr Secure Lower TMG Costs: From $2.50/g to $2.00/g Eliminate Au, Pt and/ or Pd from metallizations! Improve the Effective Cell Yield: From 70% to 95% Lower WACC: From 7% to 6%
$2.40/ W
Epi-S
ubst
rate
C
MP
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What can be done to bring the costs down?
• Huge breakthrough in reducing materials deposi2on cost.
• Light trapping to reduce film thickness. See Jim Harris’s 2013 GCEP talk at hGp://gcep.stanford.edu/symposium.
• Use concentrators. With epitaxial lifoff, 500 X concentrators might not be necessary. Trackers for 10 X concentrators are rela2vely cheap.
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Cadmium Telluride Solar Cells
CdS/CdTe
glass • Direct bandgap, Eg=1.45eV • High module production speed • Very inexpensive • 20.4 % efficiency
Image from Rommel Noufi Schematic from Bulent Basol
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CdTe: Industrial Status First Solar is the leader. It takes them 2.5 hours to make a 13.4 % module.
www.firstsolar.com; greentech media
Average Manufacturing Cost 2006: $1.40/watt 2007: $1.23/watt 2008: $1.08/watt 2009: $0.87/watt 2010: $0.77/watt 2011: $0.74/watt 2012: $0.64/watt 2013: $0.53/watt
The energy payback time is 0.8 years.
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Efficiency limits Below band gap photons not absorbed
Thermalization of excess energy
Sources of energy loss
CB
VB
Increasing VOC and decreasing JSC
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There are lots of 3rd Genera2on ideas to beat the Shockley-‐
Quiesser limit, but only one that works.
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ISC2009—Tokyo University, March 3, 2009 JSH 31
Multijunctions: The Road to Higher Efficiencies
Higher-efficiency MJ cells require new materials that divide the solar spectrum equally to provide current match
Ge provides lattice match but the bandgap is too small
GaAs1.4 eV
GaAs1.4 eV
GaInP1.8 eV
GaInP1.8 eV
0.7 eV
future generationexample structures
inproduction
1.0 eV
4 5 6 7 8 91
2 3 4
Energy (eV)
Ge0.7 eV
GaInP1.8 eV
1.25 eV
0.7 eV
GaAs1.4 eV
GaAs1.4 eV
GaInP1.8 eV
GaInP1.8 eV
0.7 eV
future generationexample structures
inproduction
1.0 eV
4 5 6 7 8 91
2 3 4
Energy (eV)
Ge0.7 eV
GaInP1.8 eV
1.25 eV
0.7 eV
Ge 0.7 eV
GaAs1.4 eV
GaAs1.4 eV
GaInP1.8 eV
GaInP1.8 eV
0.7 eV
future generationexample structures
inproduction
1.0 eV
4 5 6 7 8 91
2 3 4
Energy (eV)
Ge0.7 eV
GaInP1.8 eV
1.25 eV
0.7 eV
GaInNAs 1.0 eV
New Solar Junc2on MJ Cell
Conven2onalMJ Cell
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4-junction cell with 44.7 % efficiency at 297 suns
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Multijunction Cells are Very Expensive
Ge substrate: Bottom Cell
Ga0.99In0.01As: Middle Cell
Ga0.50In0.50P: Top Cell
R.R. King; Spectrolab Inc., AVS 54th International Symposium, Seattle 2007
• These complex structures are grown very slowly under high vacuum.
• 37 % cells can be purchased for $50,000/m2
• Concentrating the light is essential.
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Concentrating Light
Dish Shape
It is possible to track the sun and concentrate the light by 500X
Sol Focus
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Hybrid Tandems Are Intended to be a High-‐Performance Low-‐Cost Op2on
Efficiency Cost Organic 12% efficient
$30/m2
Epitaxial Crystalline
45 % efficient $40,000/m2
Hybrid 30% efficient
$100/m2
Established Technology:
Silicon or CIGS Eg ~ 1.1 eV
Low Cost Defect-Tolerant Technology: Perovskite, Organic,
Nanowires or II-VI Eg ~ 1.9 eV
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Science 339 (2013) p. 1057. Surface recombination velocity = 170 cm/s
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Stion, Khosla-Funded PV Startup, Hits 23.2% Efficiency With Tandem CIGS
Greentech Media February 24, 2014
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‘Perovskite’ Describes a Crystal Structure Class
Generic formula: ABX3
Methylammonium-lead-iodide
CH3NH3PbI3
CH3NH3+ Pb2+ I-
A B X
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2
4
6
8
10
12
14
16
2009 2010 2011 2012 2013 2014
Efficien
cy (%
)
Perovskite Solar Cells are Soaring
15.9% 15%
Snaith et al., En. Env Sci. Jan 2014 Snaith et al., Nature Sep 2013 Grätzel et al., Nature Jul 2013
Year
15.4% evaporated thin film PIN
MSSC, Al2O3 solution-processed
mesop. TiO2 2-step solution deposition
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Perovskite Solar Cells Evolved From the Dye-‐Sensi2zed Solar Cell
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Perovskites Are Compa2ble With A Planar P-‐I-‐N Architecture
Jsc = 21.5 mA/cm2 Voc = 1.07 V FF = 0.68 η = 15.4%
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Low Bandgap – q·∙Voc Loss in Perovskite Solar Cells
Material Bandgap (eV) q·∙Voc (eV) Energy loss (eV) GaAs 1.43 1.12 0.31 Silicon 1.12 0.75 0.37 CIGS ~1.15 0.74 0.41
Perovskite (CH3NH3PbI3)
1.55 1.07 0.48
CdTe 1.49 0.90 0.59 a-‐Silicon 1.55 0.89 0.66
M. Green et al. Solar cell efficiency tables (version 42) July 2013
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The traps are shallow
43 Yanfa Yan et al., Appl. Phys. Lett. 104 (2014) 63903.
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The Perovskite is a Strongly-‐Absorbing Direct Band Gap Semiconductor
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The Perovskite Bandgap can be tuned by Chemical Subs2tu2on
The band gap can be tuned from 1.57 eV to 2.23 eV by substituting bromine for iodine in CH3NH3Pb(BrxI1-x)3
data by McGehee group and Noh et al., Nano Lett. 2013
For hybrid tandem with CIGS
eV
Eva Unger
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Hybrid Tandem Architectures
2 Terminal • Fewer layers that parasitically
absorb • Module fabrication easier
4 Terminal • Easier prototyping • No current matching required • No tunnel junction or
recombination layer required
Bottom Cell
Rear Contact
Transparent Electrode
Top Cell
Transparent Electrode
Transparent Electrode Glass
Bottom Cell
Rear Contact
Top Cell
Tunnel Junction/ Recomb Layer
Transparent Electrode
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Our Semitransparent Perovskite Cells
Colin Bailie, Grey Christoforo
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Preliminary Cost Es2mates 48
Today’s Silicon Silicon-‐Perovskite
Efficiency 19.4 % 25 %
Cost/Area $153/m2 $167/m2
Cost/WaG $0.79/W $0.67/W
Expected improvements in silicon technology will take the cost below $0.5/W!
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Conclusions • Conventional silicon leads the solar cell race, but
will not take us where we need to go.
• Several technologies could take over in the next 10 years.
• We are still discovering new materials with substantially better properties.
• I think multijunction solar cells will be thin, light, cheap and > 30 % efficient.
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Final thoughts
• We have to solve the energy problem. • Any technology that has good potential to cut carbon
emissions by > 10 % needs to be explored aggressively.
• Researchers should not be deterred by the struggles
some companies are having.
• Someone needs to invest in scaling up promising solar cell technologies.