Thin Film CIGS Photovoltaics

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Thin Film CIGS Photovoltaics

• Rommel NoufiSoloPower, Inc.
• 5981 Optical Court, San Jose, CA
  95138www.solopower.com email
  rnoufi_at_solopower.com

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Acknowledgements
Bulent Basol SoloPower, Inc., California Robert
Birkmire Institute of Energy Conversion,
Delaware Bolko von Roedern, Michael Kempe,
and Joel Del Cueto National Renewable Energy
Laboratory, Colorado
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Outline
Status of the Technology Laboratory cells
Modules Challenges Ahead
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Status of PV

• 3700 MW produced world wide
• 266 MW produced in the US
• Thin Film Market Share 10 world wide, 65 in
  the US

Source PV News, Photon International, Navigant
Consultants
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Status of Thin Film PV

• Currently, FIRST SOLAR CdTe is the largest
  Thin Film manufacturing company in the US
• 277 MW in 2007
• 910 MW expected in 2009
• Demonstrated the viability of Thin Film PV
• High Throughput
• Large Scale
• Low Cost per Watt

Source First Solar.com
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PVNews Reported US Production thru 2007
Source PVNews
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CIS PV Companies

• Production of CIGS modules has also been
  demonstrated by Würth Solar, Showa Shell,
  Honda, and Global Solar Energy(lt20 MW
  manufactured)

Ascent, CO DayStar Technologies, NY/CA Energy
Photovoltaics, NJ Global Solar Energy,
AZ HelioVolt, TX ISET, CA MiaSole, CA NanoSolar
Inc., CA SoloPower, CA Solyndra, CA Stion, CA
Aleo Solar, Germany AVANCIS, Germany CIS
Solartechnik, Germany CISEL, France Filsom,
Switzerland Honda, Japan Johanna Solar Tech,
Germany Odersun, Germany PVflex,
Germany Scheuten Solar, Holland Showa Shell,
Japan Solarion, Germany Solibro,
Sweden SULFURCELL, Germany Würth Solar, Germany
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CIGS Device Structure
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Best Research-Cell Efficiencies
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Parameters of High Efficiency CIGS Solar Cells
Tolerance to wide range of molecularity Cu/(InGa)
0.95 to 0.82 Ga/(InGa) 0.26 to
0.31 Yields device efficiency of 17.5 to 19.5
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Champion Modules
Third party confirmed
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Optical Band-Gap/Composition/Efficiency
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Closing the Gap between Laboratory Cells and
Modules
Primary Focus Utilizing Lab Technology base
totranslate results to manufacturing
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CIGS Modules are Fabricated On

• I. Soda lime glass as the substrate cells are
  monolithically integrated using laser/mechanical
  scribing.

Courtesy of Dale Tarrant, Shell Solar
Monolithic integration of TF solar cells can lead
to significant manufacturing cost reduction
e.g., fewer processing steps, easier automation,
lower consumption of materials.
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CIGS Modules are Fabricated On (cont.)
The number of steps needed to make thin film
modules are roughly half of that needed for Si
modules. This is a significant advantage.
CIGS Modules Process Sequence
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CIGS Modules are Fabricated On (cont.)

• II. Metallic web using roll-to-roll deposition
  individual cells are cut from the web assembled
  into modules.

III. Plastic web using roll-to-roll deposition
monolithic integration of cells.
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Challenges
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Long-Term Stability (Durability)

• Improved module package allowed CIGS to pass damp
  heat test (measured at 85C/85 relative
  humidity).
• CIGS modules have shown long-term stability.
  However, performance degradation has also been
  observed.
• CIGS devices are sensitive to water vapor e.g.,
  change in properties of ZnO.
• - Thin Film Barrier to Water Vapor
• - New encapsulants and less aggressive
  application process
• Stability of thin film modules are acceptable
  if the right encapsulation process is used.
• Need for better understanding degradation
  mechanisms at the prototype module level.

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Processing Improvements

• I. Uniform Deposition over large area
• (a) significant for monolithic integration
• (b) somewhat relaxed for modules made from
  individual cells
• II. Process speed and yield some fabrication
  approaches have advantage over others
• III. Controls and diagnostics based on material
  properties and film growth benefits throughput
  and yield, reliability and reproducibility of the
  process, and higher performance

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Processing Improvements (cont.)

• IV. Approaches to the thin film CIGS Deposition
• 1. Multi-source evaporation of the elements
• - Produces the highest efficiency
• - Requires high source temperatures, e.g., Cu
  source operates at 1400-1600C
• - Inherent non-uniformity in in-line processing
• - Fast growth rates my become diffusion limited
• - Complexity of the hardware with controls and
  diagnostic
• - One of a kind hardware design and construction
• - Expensive
• - Throughput, and material utilization need
  improvement

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Processing Improvements (cont.)

• IV. Approaches to the thin film CIGS Deposition
  (cont.)
• 2. Reaction of precursors in Se and/or S
  (Selenization)to form thin film CIGS two stage
  process
• - Variety of materials delivery approaches
• (a) sputtering of the elements
• (b) electroplating of metals or binaries
• (c) Printing of metal (or binaries)
  particles on substrate
• - Reaction time to form high quality CIGS films
  is limited by reaction/diffusion
• - Modules on glass are processed in batch mode
  in order to deal with long reaction time
• - Flexible roll-to-roll requires good control of
  Se vapor and reaction speed
• - Ga concentration thru the film is
  inhomogeneous limiting performance

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Processing Improvements (cont.)

• V. Reduction of the thickness of the CIGS film
• Reduces manufacturing costs higher throughput
  and less materials usage
• More sensitive to yield, e.g. threshold
  thickness non-uniformity, pin-holes
• Challenge is to reduce thickness and maintain
  performance

Thin Cells Summary
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0.4 µm cell - Optical
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Toward Low Cost

• Module performance is a significant determining
  factor of cost
• Cell processing affects performance
• The benefits of each process and how it is
  handled in manufacturing need to be assessed
• To date, relatively high cost methods adapted for
  manufacturing

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SoloPower Advances

• SoloPower has developed a low cost
  electro-deposition process to manufacture CIGS
  solar cells and modules
• A conversion efficiency approaching 14 has been
  confirmed at NREL
• Modules have been manufactured demonstrating
  process flow

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The Electrodeposition Process

• Hardware is low cost
• Can be high throughput once the hardware is tuned
  to the specifics of the process
• Near 100 material utilization
• Pre-formed expensive materials are not required,
  e.g. sputtering targets, nano-particles
• Crystallographically oriented CIGS films with
  good morphology and density have been
  demonstrated
• Thickness and composition control of the
  deposited films are integral part of the process
• Readily scalable

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C2318
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Future Commercial Module Performance

• Based on todays champion cell results and a
  module/cell-ratio of 80

Source Bolko Von Roedern, PVSC 2008, IEEE May
12,2008, San Diego
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Best Production-LinePV Module Efficiency Values
From Manufacturers Web Sites Compiled by Bolko
von Roedern, September 2008
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Best Production-LinePV Module Efficiency Values
(cont.)
From Manufacturers Web Sites Compiled by Bolko
von Roedern, September 2008
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Further Reading Sources
Accelerated UV Test Methods for Encapsulants of
Photovoltaic Modules Stress Induced
Degradation Modes in CIGS Mini-Modules Michael
D. Kempe et al, Proceedings of the 33rd
IEEE,PVSC, May 11, 2008, San Diego Modeling of
Rates of Moisture Ingress into Photovoltaic
Modules Michael D. Kempe, Solar Energy
Materials Solar Cells, 90 (2006)
27202738 Stability of CIS/CIGS Modules at the
Outdoor Test Facility Over Two DecadesJ.A. del
Cueto, S. Rummel, B. Kroposki, C. Osterwald, A.
Anderberg,Proceedings of the 33rd IEEE,PVSC ,
May 11, 2008, San Diego Pathways to Improved
Performance and Processing of CdTe CuInSe2
Based Modules Robert W. Birkmire, Proceedings
of the 33rd IEEE,PVSC, May 11, 2008, San
Diego The Role of Polycrystalline Thin-Film PV
Technologies in Competitive PV Module Markets
Bolko von Roedern and Harin S. Ullal,
Proceedings of the 33rd IEEE,PVSC , May 11,
2008, San Diego High Efficiency CdTe and CIGS
Thin Film Solar Cells Highlights and Challenges
Rommel Noufi and Ken ZweibelProceedings of the
4th WCPEC, May 7, 2006, Hawaii
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• The End

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PV Energy Cost
DOE, Solar America Initiative Projections and
Goals

• Costs are constant 2005 dollars
• Residential and commercial are cost to customer
• Utility is cost of generation

Solar Electricity cost
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CIGS Manufacturing
Requirements for a CIGS absorber film growth
technique for high efficiency devices include

• For high quality
• Stoichiometric control Cu/(GaIn),
  Ga/(GaIn), S/(SSe)
• Good microstructure
• Bandgap control
• For low cost
• Low cost equipment
• High materials utilization