The main objective of the IEA-PVPS Task 13 Report on “Designing New Materials for Photovoltaics: Opportunities for Lowering Cost and Increasing Performance through Advanced Material Innovations” is to provide a global survey of technical efforts aimed at lowering cost and increasing performance and reliability of PV modules by employing new designs, materials and concepts. Furthermore, the report aims to (1) increase the exchange of information about promising materials and design concepts, (2) provide the means for increasing the value of PV modules, (3) provide recommendations on characterization methods for new technologies and (4) give input regarding new requirements for standardization. This paper focuses on describing the motivation, benefits, and challenges for new photovoltaic material and module developments.

1. IEA PVPS Task 13 Introduction
Ulrike Jahn, VDE Renewables / Boris Farnung, VDE Renewables
2021
IEA PVPS Task 13
Performance, Operation and Reliability of PV Systems

2. 2
Setting the scene: PV markets
Annual installed PV capacity Total installed PV capacity
Source: IEA PVPS Task 1 Trends Report (2020)

3. 3
Setting the scene for IEA PVPS: PV is moving in …
• … fast technology progress
• … installed capacities
• … record prices and LCOE, announced lowest PPAs ≈ 13 - 15 USD/MWh
• … increasing competitiveness
• … business models
• … broadening applications – “PV going everywhere”
• … serving different customers
• … to the energy system
• … to the TW era
• … to become mainstream!

4. 4
IEA PVPS TCP in a nutshell
• 32 members - 27 countries covering 5 continents,
European Commission, 4 associations
• A truly global and unbiased network of PV expertise
• Representing main stakeholders in R&D, industry, implementation and policy
• Covering a large majority of worldwide production, applications and markets
• Mission: “To enhance the international collaborative efforts which facilitate the
role of photovoltaic solar energy as a cornerstone in the transition to sustainable
energy systems”

5. 5
Working along the value chain
Concepts
Technologies
Solutions
Applications
Components Systems Integration
Research Market
PVPS network and testbed

6. 6
International Cooperation: Role and Benefits
• Look into the present and future of PV worldwide
• Identify and understand relevant issues for large scale deployment
• Collect and exchange facts and experience
• Analyse precisely and draw appropriate lessons learned
• Communicate in a clear and targeted way
• Provide sound advice to different stakeholders, including policy makers
• Accelerate the development and learning, prevent errors to be repeated
• Identify successful policy approaches and business models
• Provide long term market, environmental and policy insights
• Expand and accelerate the deployment

7. 7
8 Active PVPS Tasks…
• Task 1 - Strategic PV Analysis and Outreach
• Task 12 - PV Sustainability
• Task 13 - Performance, Operation and Reliability of Photovoltaic Systems
• Task 14 - Solar PV in the 100% RES Power System
• Task 15 - Enabling Framework for the Acceleration of BIPV
• Task 16 - Solar Resource for High Penetration and Large Scale Applications
• Task 17 - PV and Transport (new 2018)
• Task 18 - Off-Grid and Edge-of-Grid Photovoltaic Systems (new 2019)

8. 8
Task 13: New Module Concepts and System Designs
PV Modules
• Encapsulants, backsheets
• Bifacial module designs
• Shingled cells, half-cell, new interconnections
• Glass-glass, frameless, lightweight
PV Systems
• PV with energy storage or other combinations
• High DC/AC ratios and 1500+ Vdc
• Module/string-scale power electronics
• Floating PV, Agriculture PV
• PV tracking technologies and issues

9. 9
Task 13: Performance of Photovoltaic Systems
Impact of
Soiling
Advanced
Diagnostics
Climatic
Rating
Yield
Assessment
Performance
Loss Rate
Shared
Data
Shared
Methodologies

10. 10
Task 13: Monitoring – Operation & Maintenance of PV Power Plants
• Increase the knowledge of methodologies to
assess technical risks and mitigation measures
in terms of economic impact and effectiveness
during operation.
• Provide best practice on methods and devices
to qualify PV power plants in the field.
• Compile guidelines for O&M procedures
in different climates and to evaluate
how effective O&M concepts will affect
the quality of power plants in the field.

11. 11
Task 13: Dissemination
Task 13 Reports:
12 Technical
reports
published in the
last year
www.iea-pvps.org

12. Motivation, benefits, and opportunities for new
material & module developments
Gernot Oreski, Polymer Competence Center Leoben, Austria
Graz, 15.06.2021
gernot.oreski@pccl.at

13. 13
IEA Task 13
Report IEA-PVPS T13-13:2021, January 2021
New IEA Task 13 report on DESIGNING
NEW MATERIALS FOR PHOTOVOLTAICS
✓ https://iea-pvps.org/key-
topics/designing-new-materials-for-
photovoltaics/
▪ Global survey of technical efforts aimed at
lowering cost and increasing performance
and reliability of PV modules by employing
new designs, materials and concepts

14. 14
Introduction
G.C. Eder, Y. Voronko, W. Mühleisen, K. Knöbl, P. Kefer,
C. Panhuber, Long-Term Reliability of PV-Modules in Alpine
Environment, 37th European Photovoltaic Solar Energy Conference
and Exhibition, 2020, 6CV.2.9
▪ Loser PV system (Austrian alps)
− Installation: 1988
− 30kWp on 232m²
− Power label: ~ 50W per module
Annual degradation after more than 30 years
Siemens
Power loss: 13.4%
0.45% / year
Kyocera
Power loss: 6.1%
0.20% / year
ARCO
Power loss: 20.4%
0.68% / year

15. 15
Introduction
G.C. Eder, Y. Voronko, W. Mühleisen, K. Knöbl, P. Kefer, C. Panhuber, Long-Term Reliability of PV-Modules in
Alpine Environment, 37th European Photovoltaic Solar Energy Conference and Exhibition, 2020, 6CV.2.9
Degradation modes and rates
depend on material interactions
▪ Different degradation behavior for
different modules under identical micro-
climatic conditions
▪ Bill of materials of PV modules important
for understanding PV module
degradation modes
▪ Remember: Also report PV module
material composition and not just
electrical data of systems
Why aren't PV modules built like this anymore?

16. 16
Introduction
Price learning curve
Average crystalline silicon
PV module efficiency
Source: Photovoltaics Report - Fraunhofer ISE
https://www.ise.fraunhofer.de/content/dam/ise/de/documents/publications/studies/Photovoltaics-Report.pdf

17. 17
©Michael Woodhouse, Launch Webinar of the 2021 ITRPV report, April 29th 2021

18. 18
Motivation for new materials and module designs
▪ Reduction and replacement of expensive
materials
- Solar cell thickness
- Silver content
- Glass thickness
- Replacement of Fluoropolymers
Decrease of LCOE: Cost reduction and performance improvement
Fraunhofer ISE Photovoltaics Report
https://www.ise.fraunhofer.de/de/veroeffentlichungen/studien/photovoltaics-report.html International Technology Roadmap for Photovoltaic (ITRPV) (https://itrpv.vdma.org/en/)
▪ Significant reduction of wafer thickness
and silicon usage
▪ Reduction of front glass thickness from
4mm to values between 2 and 3mm
▪ Significant reduction of silver
- From 400mg in 2007 to ~50-100mg in 2020

19. 19
Motivation for new materials and module designs
▪ Acceleration of manufacturing
process
- Ultra Fast curing EVA
- Thermoplastic encapsulants
▪ Performance increase
- Interconnection: Reduction of
resistive losses and cell
shadowing
- Encapsulants and backsheets with
enhanced optical properties
▪ Production related cost decrease
- Wafer size
Decrease of LCOE: Cost reduction and performance improvement
https://www.rena.com/en/products/large-wafer-wet-processing/
500 1000 1500 2000 2500
0.0
0.2
0.4
0.6
0.8
1.0
Hemispherical
reflectance
[-]
Wavelength [nm]
PPF
PP
https://doi.org/10.1016/j.solmat.2021.110976
Increase in PMPP
+ 2.5% with EVA
+ 2.5% with TPO
+ 1.5% with POE

20. 20
Motivation for new materials and module designs
▪ Sustainability and legal regulations
- Ecodesign
- Recyclability
- Replacement of rare or harmful materials
Ecodesign of PV: JRC Sevilla & JRC Ispra
http://susproc.jrc.ec.europa.eu/solar_photovoltaics/index.html
https://wwg.eu.com/de/news-
blog-de/in-2020-elektrische-und-
radioelektrische-produkte-in-
eacu-should-comply-with-rohs/
Raw
material
Production
Distribution
Use/Re-use
Disposal /
Recycling
„from cradle to grave“

21. 21
Motivation for new materials and module designs
▪ New technological requirements
- Wafer technology
- New cell and interconnection technologies
- New module designs
Multiwires
Shingling
- PERC and HJT will become dominant
cell technologies
- Half cells will gain more market share
- Module sizes increase
New cell technologies
© Trina Solar
Interconnection
© Meyer Burger
https://doi.org/10.1016/j.apsusc.2020.145420
Structured foil
https://www.sunportpower.com/

22. 22
Motivation for new materials and module designs
“One module type fits all” approach
Strong dependence of module
degradation rate on location
Ascencio-Vásquez, J.; Kaaya, I.; Brecl, K.; Weiss, K.-A.; Topič, M. Global Climate Data
Processing and Mapping of Degradation Mechanisms and Degradation Rates of PV
Modules. Energies 2019, 12, 4749. https://doi.org/10.3390/en12244749

23. 23
Motivation for new materials and module designs
PV systems designed for specific environmental conditions
© Baywa r.e.
Floating PV
Desert PV Vehicle integrated PV
© Sono Motors
PV in transport infrastructure
© AIT
Building integrated PV
© Ertex Solar
© Fraunhofer ISE
Agri PV

24. 24
Challenges for new materials and components
▪ External and internal stress factors influence performance and long-term reliability of PV modules
▪ The materials in PV modules have to withstand extremely challenging micro-climatic conditions
External factors
▪ Irradiation
▪ Temperature
▪ Humidity
▪ Atmospheric
gases
▪ Mechanical loads
(Wind, snow)
Internal factors
▪ Bill of material
▪ Processing effects

25. 25
Challenges for new materials and components
▪ Check of compatibility of PV module components will get more and more
important in the future, as the variety on materials and components will grow
▪ Emergence of new degradation modes (e.g. LeTid, PID…. )
Corrosion: Broad variety
of new ribbon materials,
interconnection
technologies and
encapsulant films
Backsheet yellowing: Migration
of additives into backsheet -
encapsulant interface are main
cause for backsheet yellowing
Adhesion - delamination:
- Adhesion to glass and solar cell
strongly dependent of lamination
parameters
- Surface treatment of backsheets
usually optimized for adhesion to EVA
but not alternative encapsulants Constant need for adaption of
test methods and standards

26. 26
Failure scenarios of c-Si PV modules
Component selection
Module lamination Material degradation
Mostly avoidable: Extensive R&D,
quality and reliability testing needed
Can be delayed to some extent
with proper stabilization
Köntges et al. (2014) IEA-PVPS Task 13 Report on
“Review of Failures of Photovoltaic Modules”

27. 27
Testing of new materials for PV modules
Material or film
supplier
▪ Different levels
with increasing
effort in sample
preparation and
test procedures
▪ All levels of testing
needed in order to
guarantee high
quality and
reliability
High number of
tested specimen
High cost & effort
of testing

28. 28
2010
2010-2015
2015 -
New failure modes
Major motivation for
backsheet development:
Improved raw material
supply
✓ TPT backsheet dependent
on supply of PVF
✓ Strong demand growth
could not be met with
PVF supply
Market introduction of co-
extruded polyamide based
backsheets (AAA)
Around 12 GW of PV was
sold with AAA backsheets
Unforeseen cracking of
AAA backsheets after
some years in the field
Longitudinal cracks
along the busbars
Square crackes in the
cell interspaces
Chalking &
microcracks
G. Eder, Y. Voronko, G. Oreski, W. Mühleisen, M. Knausz, A. Omazic, A. Rainer, C. Hirschl, H. Sonnleitner (2019) „Error analysis of aged
modules with cracked polyamide backsheets“, Solar Energy Materials and Solar Cells 203, https://doi.org/10.1016/j.solmat.2019.110194
Polyamide backsheet failure

29. 29
New failure modes
Polyamide backsheet failure
So why have the failure mechanisms of
AAA not been observed in the lab?
Formation of cracks is a two-step process
▪ Reduction of fracture toughness due to
long term exposure at high temperatures
or UV irradiation
▪ Continuously occurring mechanical and
thermo-mechanical loads → internal
stresses due to constrained thermal
expansion of the backsheet
What was done?
What should have been done?
Sequential / combined stress testing
Single stress testing
▪ Material degradation was observed after
DH and UV exposure of the film, but no
cracking due to missing thermo-
mechanical loads
▪ Thermal load of TC too low to induce
material degradation of the backsheet
▪ G. Eder, Y. Voronko, G. Oreski, W. Mühleisen, M. Knausz, A. Omazic, A. Rainer, C. Hirschl, H.
Sonnleitner (2019) „Error analysis of aged modules with cracked polyamide backsheets“, Solar
Energy Materials and Solar Cells 203, https://doi.org/10.1016/j.solmat.2019.110194
▪ Owen-Bellini, M., Moffitt, S.L., Sinha, A. et al. Towards validation of combined-accelerated
stress testing through failure analysis of polyamide-based photovoltaic backsheets. Sci Rep
11, 2019 (2021). https://doi.org/10.1038/s41598-021-81381-7
▪ Lyu, Y, Fairbrother, A, Gong, M, et al. Drivers for the cracking of multilayer polyamide‐based
backsheets in field photovoltaic modules: In‐depth degradation mapping analysis. Prog
Photovolt Res Appl. 2020; 28: 704– 716. https://doi.org/10.1002/pip.3260

30. 30
New failure modes
Current situation in lab testing
▪ Currently the industry relies mostly on
extended IEC testing for qualification
of new module materials and module
designs
▪ Material interactions and
incompatibilities are getting in the
focus of material and module
developers
▪ Simultaneous combined or sequential
stresses (UV, humidity, temperature
and thermo-mechanical load) lead to
more realistic degradation of PV
modules in lab testing
Gambogi et al. (2018) doi: 10.1109/PVSC.2018.8547260.
Owen-Bellini et al. (2020) https://doi.org/10.1002/pip.3342
▪ Recently for the first time backsheet
cracks have been reproduced by an
indoor accelerated aging test

31. 31
Conclusion & Outlook
▪ Motivation for new materials and
module designs
- Decrease of LCOE: Cost reduction and
performance improvement
- New technological requirements
- Sustainability and legal regulations
- PV systems designed for specific
environmental conditions
▪ Challenges
- Long term stability is determined by bill of
materials and their material interactions
- Each material combination should be tested
thoroughly before introduction into the market
- Single stress testing often does not reveal
certain degradation modes observed in the
field → combined or sequential stress testing
necessary
▪ Check of compatibility of PV
module components will get more
and more important in the future, as
the variety on materials and
components will grow
- Emergence of new degradation modes
- Constant need for adaption of test
methods and standards
▪ Design matching of components
and materials may reduce
degradation rates or avoid certain
degradation modes
Better understanding of PV module and material
degradation processes is a precondition for a
successful development of new components and
reliable PV module designs

32. iea-pvps.org Thanks to all the contributors!
✓ Chiara Barretta, Luis Castillon (Polymer Competence Center Leoben (PCCL), Austria)
✓ Joshua Stein (Sandia National Labs, USA)
✓ Gabriele Eder (Austrian Research Institute for Chemistry and Technology (OFI), Austria)
✓ Karl Berger (Austrian Institute of Technology (AIT), Austria)
✓ Laura S. Bruckman, Roger H. French, Raymond Wieser, Sameera Nailn Venkant, Menghong Wang (Case
Western Reserve University (CRWU), USA)
✓ Jan Vedde (European Energy, Denmark)
✓ Karl-Anders Weiss (Fraunhofer ISE, Germany)
✓ Tadanori Tanahashi (National Institute of Advanced Industrial Science and Technology (AIST), Japan)
✓ William Gambogi, Kaushik Roy Choudhury (DuPont, USA)
✓ Mauro Caccivio (SUPSI, Switzerland)
✓ Markus Klenk, Hartmut Nussbaumer (ZHAW, Switzerland)
✓ Gianluca Cattaneo (CSEM, Switzerland)
✓ Sang Han (Osazda Energy, USA)
✓ Hoi Ng (Sunpower, USA)
✓ David C. Miller (NREL, USA)
✓ Samuli Ranta (Turku University of Applied Sciences, Finland)
✓ Marc Köntges (ISFH, Germany)

33. Materials Innovations in PV: Challenges for Reliability
Laura S. Bruckman,
Associate Research Professor
Case Western Reserve University, Cleveland, OH, USA

34. PVPS
2
What is IEA PVPS?
• The International Energy Agency (IEA), founded in 1974, is an autonomous body within the
framework of the Organization for Economic Cooperation and Development (OECD).
• The Technology Collaboration Programme was created with a belief that the future of energy
security and sustainability starts with global collaboration. The programme is made up of
thousands of experts across government, academia, and industry dedicated to advancing
common research and the application of specific energy technologies.
• The IEA Photovoltaic Power Systems Programme (PVPS) is one of
the Technology Collaboration Programme established within the
International Energy Agency in 1993
• 32 members - 27 countries, European Commission, 4 associations
• “To enhance the international collaborative efforts which facilitate the role of photovoltaic solar
energy as a cornerstone in the transition to sustainable energy systems”

35. PVPS
3
New PV Materials and the Challenge for Reliability
PV Modules are growing at an amazing rate
● New Cell types, manufacturing, sizes
● New applications (floating, building integrated, etc)
Require New Materials
● for increased performance
● lifetime and durability
● for the new applications
Prevent large scale degradation or failure in these new materials
● requires a good understanding of degradation
● multiple design choices
● multiple stress conditions

36. PVPS
4
Flexible Frontsheets
Many applications need lightweight PV modules
▪Like Building Integrated Solar
Looking for alternatives to ETFE and FEP (reduce cost)
Reliability in these materials are difficult
▪Current lightweight polymers are not suitable for lifetime of PV modules
▪ to issues in long term stability,
▪ thermo-mechanical behavior and compatibility with the encapsulant
▪Need to be stabilized due to photothermal degradation
Solar Quantum
Efficiency
Weighted
Transmission
(SQEWT)
UV Durability is a concern
Still need to incorporate
• materials in PV modules for exposures
• combined stressors

37. PVPS
5
Encapsulants
Reduction of LCOE is the main driving factor for new developments
● Replacement of expensive materials with more economic ones-
● Increase of quality and reliability (compatibility of new cell types)
● Addition of new features (e.g. enhanced optical properties, selective permeability etc.)
●
Dominant materials: EVA encapsulants and PET/PVDF or PET/PVF backsheets
● more than 90% market share [Taiyang News]
http://taiyangnews.info/reports/market-survey-backsheets-encapsulation-2020/

38. PVPS
6
Encapsulants: Polyethylene copolymers
New Encapsulants: Polyethylene copolymers
• No vinyl acetate group (different from EVA)
• No formation of acetic acid
• Cross-linking polyolefin elastomers (POE)
• And non-cross-linking TPO
■ Thermoplastic polyolefin
• Less co-monomer content than EVA
• Higher volume resistivity than EVA
• Lower water vapor transport rates than EVA
• Similar transmission profile

39. PVPS
7
Encapsulants: Polyethylene copolymers
•
Multiple degradation
studies show stability
after accelerated
exposures
Mini-modules damp heat exposures
IEC TS
62788-7-2 A3
UV weathering
of films

40. PVPS
8
Encapsulants: Silicone
Polydimethylsiloxane (PDMS) and derivatives
● historically used in the 1980s
● due to its stability and durability (reported in literature in PV)
● however, cost was the driving factor behind it’s limited use in PV (viscous liquid application)
● provides corrosion protection, no discoloration, PID inhibitive properties
● high optical transmission in the UV
New silicone encapsulant-sheet
● laminate under conventional
○ vacuum-heat lamination process
● similar properties of
○ the previous liquid form
● need reliability data
No corrosion in EL images
● after 6000 hrs of damp heat
● need multi-stress and real-world data

41. PVPS
9
Metalization: Metal Matrix Composites
Advanced Composite Metallization
● multiwalled carbon nanotubes
● bridging cracks in metalization
Fractional change in resistance along parallel gridlines
● measure of gridline failure in TC
● lower median

42. PVPS
10
Multi-wire Interconnection
Busbar-less interconnection
● with multi wires (18 wires)
● front metalization fingers
Reduce the amount of silver
● driven just like the increase in busbars
Increase cell area available for light capturing
Low temperature contact processing
● Beneficial for SHJ cells
Max Power for Damp Heat and Thermal Cycling
(72 Cell module)
SmartWire Connection
Technology (SWCT™)

43. PVPS
11
Electrically conductive adhesives (ECA)
Adhesive filled with conductive particles
● polyimides typically used
● Silver most common conductor (gold, nickel, copper, tin)
Advantage
● No busbars necessary
● Compatible with all types of ribbons (Cu, SnPb, AG, SnPb…)
● Enables interconnection techniques
○ such as shingling or conductive backsheets
● Low temperature processing, higher resolution printing, easier handling
○ less thermomechanical stress on cells

44. PVPS
12
Electrically conductive adhesives (ECA)
Chemical composition and cure
conditions have a large influence on
visco-elastic material properties and
fracture behavior
No harmful interactions between
ECA types and encapsulant
during lamination and aging tests
Migration of hardener into the surrounding
encapsulation material (no silver migration)

45. PVPS
13
Backsheets
Reduction of LCOE is the main driving factor for new developments
● Replacement of expensive materials with more economic ones-
● Increase of quality and reliability (compatibility of new cell types)
● Addition of new features (e.g. enhanced optical properties, selective permeability etc.)
Dominant materials: EVA encapsulants and PET/PVDF or PET/PVF backsheets
● more than 90% market share [Taiyang News]
http://taiyangnews.info/reports/market-survey-backsheets-encapsulation-2020/

46. PVPS
14
Transparent Backsheets
Bifacial Modules (already deployed commercially)
● UV stability and high light transmission
● which is critical to the output power of the bifacial module
Polymer backsheet (compared to glass-glass module design)
● Easier transport and installation due to lower weight
● Design open for diffusion (H2
O, O2
, acetic acid)
Challenge:
● be transparent in the cell range
● remove TiO2
● still protecting PET core and
inner layers
● white grid layer to protect
between cells
PVF

47. PVPS
15
Co-extruded Backsheets
Co-extruded backsheets in 2010
● cost reduction
○ move away from PVF and PVDF
○ to PET, PA, PP, PE
● thickness optimization
● processing steps reduced
● Selective permeability: Vapor transport rates
○ high acetic acid (AATR)
○ low water (WVTR)
Cracking in AAA backsheets
>90% failure rate, ~11GW of modules
First coextruded backsheet 2009-2010
Longitudinal Cracks, Square Cracks
MicroCracks (not pictured)
Caused by different degradation mechanisms

48. PVPS
16
Non-uniform Degradation of Backsheets
Environmental stresses are not uniformly applied to PV packaging materials:
Accelerated degradation in certain locations, unique failure modes:
● In between solar cells
● Areas in proximity to ribbon wire interconnects
● Interactions with encapsulant and backsheet
16
Backsheets: Correlation of Long-Term Field Reliability with Accelerated Laboratory Testing https://www.osti.gov/biblio/1529111

49. PVPS
17
Micro-climates of PV Modules depend on mounting
Similar rear-side irradiance distribution with YI pattern
● Measurement: rear-side irradiance measured
● Simulation: physical model for ordinary PV rack[1]
Inhomogeneous rear-side irradiance
● May cause non-uniform backsheet degradation
● Within one rack in the PV site
[1] Yusufoglu, U. A., et al., (2014). Simulation of energy production by bifacial modules with revision of ground reflection. Energy Procedia, 55, 389-395.
[2] Elwood, T., & Simmons-Potter, K. (2017, August). Comparison of modeled and experimental PV array temperature profiles for accurate interpretation of module performance and
degradation. In Reliability of Photovoltaic Cells, Modules, Components, and Systems X (Vol. 10370, p. 1037006). SPIE.
17
Rear-side
irradiance
Measurement
17
Backsheets: Correlation of Long-Term Field Reliability
with Accelerated Laboratory Testing
https://www.osti.gov/biblio/1529111

50. PVPS
18
Pollution Effect on Backsheet
18
Air pollutants
● NO2
causes yellowing of polyamide[1]
● More prominent effect of NO2
:
○ Roof mounted modules
○ Potentially higher irradiance & temperature
● Lower yellowness index value
○ With grass ground cover
Ground cover changes
● Albedo
● Temperature
[1] Pokholok, T. V., Gaponova, I. S., Davydov, E. Y., & Pariiskii, G. B. (2006). Mechanism of
stable radical generation in aromatic polyamides on exposure to nitrogen dioxide. Polymer
degradation and stability, 91(10), 2423-2428.
Changshu, China,
roof mounted
Changshu, China, grass
ground cover
Backsheets: Correlation of Long-Term Field Reliability with Accelerated Laboratory Testing. https://www.osti.gov/biblio/1529111

51. PVPS
19
Backsheet Film Study
23 different backsheets, 12 suppliers, 9 layering combinations
• 1.5 x 2” samples cut to align with machine and transverse directions
• Freestanding configuration (no mounting to glass or other substrate)
• Layers listed outer / core / inner (thickness from optical microscopy data)
• 10 measurements for each layer (largest standard error 3.25 μm)
4 different exposures
• Indoor accelerated: 8 steps of 500 hours each = 4,000 hours total exposure
■ Hot QUV: continuous irradiance from UVA-340 lamps at an intensity of
1.55 W/m2
/nm at 340 nm and a chamber temperature of 70°C
■ Cyclic QUV: cyclic exposure of 8 hours of Hot QUV followed by 4
hours of darkness and condensing humidity at 50°C
• Outdoors in Cleveland, OH: 6 steps of 2 months = 12 months total exposure
■ Real-world 1x: natural, full-spectrum solar irradiance and exposure to
all weather conditions
■ Real-world 5x: identical to Real-World 1x with the addition of
concentrating aluminum mirrors to increase the irradiance
approximately five times
Klinke, A. G., Gok, A., Ifeanyi, S. I., & Bruckman, L. S. (2018). A
non-destructive method for crack quantification in photovoltaic
backsheets under accelerated and real-world exposures. Polymer
Degradation and Stability, 153, 244-254.

52. PVPS
20
Crack Propagation Over Time
Density, depth, and number of cracks increases with exposure
Can visualize propagation of cracks through backsheet layers
Inner (EVA)
Core (PET)
Outer (PVF)
Klinke, A. G., Gok, A., Ifeanyi, S. I., & Bruckman, L. S.
(2018). A non-destructive method for crack
quantification in photovoltaic backsheets under
accelerated and real-world exposures. Polymer
Degradation and Stability, 153, 244-254.

53. PVPS
21
Sam
ple
Layers Thickness (μm) Accelerated
QUV
Real-World
Layers Total Cyclic Hot 5x 1x
FPE1 PVF/PET/
EVA
18 / 140 /
70
229 P-L-D
-Bl
P-L-Bl n n
FPE2 46 / 118 /
114
278 P-Br P-Br-D
-Bl
P-Br P
FPE3 44 / 118 /
120
282 P-L P-Br n n
FPP1 PVF/PET/
PE
11 / 64 /
203
278 P-Br P-Br-D n n
FPP2 23 / 261 /
49
332 P P-Br P n
PPE1 PET/PET/
E
33 / 104 /
99
236 P-Bl P-L n n
PPE2 24 / 74 /
166
264 P-Br-
Bl
P-Br P n
Types of cracks:
none (n) parallel cracks (P)
mudflat cracks (M) branching cracks (Br)
localized cracks (L) delamination (D)
blistering (Bl)
Types of Cracking Observed - Sample/Exposure Combinations
Layering combinations with no cracking:
• AAA (polyamide), DPD (PVDF x2), DPE
(PVDF, EVA), and FPF (PVF X2)
Polyamide (AAA) cracks are common in the literature
Performance of materials that cracked and were
measured (least to most)
• By Dn, avg
: FPP (1.56), FPE (1.84), and PPE (2.23)
• By Cn, avg
: FPP (3.94), FPE (5.49), and PPE (7.00)
• Ranking remains the same regardless of metric
used
Accelerated exposures far exceed the Cn
values observed
in the real-world
Cyclic exposure caused the most cracks
1X exposure only caused 1 backsheet type of 23 to crack
Klinke, A. G., Gok, A., Ifeanyi, S. I., & Bruckman, L. S. (2018). A non-destructive method for crack
quantification in photovoltaic backsheets under accelerated and real-world exposures. Polymer Degradation
and Stability, 153, 244-254.

54. PVPS
22
New Materials and Reliability
New materials show great promise to
● reduce cost
● increase lifetime
Need to be aware of the interactions between materials
● ex. Encapsulant and Backsheet degradation are inter related
● temperature ranges needed for lamination
● grades of materials (different crystallinity, quality of additives)
Need to obtain real-world data on
● materials, components, and system (PV module)
● accelerated stresses need to be able to mimic real degradation
New materials need to first consider
● reliability, durability, and lifetime
● may not always be the most cost effective option

55. PVPS
23
Thanks to all IEA PVPS Task 13 ST 1.1 Contributors