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Thin Film CIGS Photovoltaics


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Title: Thin Film CIGS Photovoltaics

Thin Film CIGS Photovoltaics
  • Rommel NoufiSoloPower, Inc.
  • 5981 Optical Court, San Jose, CA email

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
Status of the Technology Laboratory cells
Modules Challenges Ahead
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
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
PVNews Reported US Production thru 2007
Source PVNews
CIS PV Companies
  • Production of CIGS modules has also been
    demonstrated by Würth Solar, Showa Shell,
    Honda, and Global Solar Energy(lt20 MW

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
CIGS Device Structure
Best Research-Cell Efficiencies
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
Champion Modules
Third party confirmed
Optical Band-Gap/Composition/Efficiency
Closing the Gap between Laboratory Cells and
Primary Focus Utilizing Lab Technology base
totranslate results to manufacturing
CIGS Modules are Fabricated On
  • I. Soda lime glass as the substrate cells are
    monolithically integrated using laser/mechanical

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.
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
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.
Long-Term Stability (Durability)
  • Improved module package allowed CIGS to pass damp
    heat test (measured at 85C/85 relative
  • CIGS modules have shown long-term stability.
    However, performance degradation has also been
  • 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.

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

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
  • - One of a kind hardware design and construction
  • - Expensive
  • - Throughput, and material utilization need

Processing Improvements (cont.)
  • IV. Approaches to the thin film CIGS Deposition
  • 2. Reaction of precursors in Se and/or S
    (Selenization)to form thin film CIGS two stage
  • - 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

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

Thin Cells Summary
0.4 µm cell - Optical
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

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

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
  • Thickness and composition control of the
    deposited films are integral part of the process
  • Readily scalable

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
Best Production-LinePV Module Efficiency Values
From Manufacturers Web Sites Compiled by Bolko
von Roedern, September 2008
Best Production-LinePV Module Efficiency Values
From Manufacturers Web Sites Compiled by Bolko
von Roedern, September 2008
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
  • The End


PV Energy Cost
DOE, Solar America Initiative Projections and
  • Costs are constant 2005 dollars
  • Residential and commercial are cost to customer
  • Utility is cost of generation

Solar Electricity cost
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