Barrier Coatings and Effects of Moisture on SSI CIGSS Cells

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Barrier Coatings and Effects of Moisture on SSI
CIGSS Cells

• Larry Olsen, Sambu Kundu and Mark Gross
• Pacific Northwest National Laboratory (PNNL)

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Outline Of Presentation

• Introduction
• Background
• 3. Approach To Studies With SSI Circuits
• 4. Results For Accelerated Tests
• 5. Key Results / Future Work

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PNNL Program Barrier Coatingsand Stability of
Thin Film Solar Cells

• PROGRAM
• Funded By NREL As Part of the Thin Film
  Partnership
• OBJECTIVE
• Develop Low Cost Barrier Coatings For Thin Film
  Solar Cells
• Investigate Mechanisms Influencing Cell
  Stability
• APPROACH
• Utilize Multilayer Coating Technology Developed
  at PNNL For OLEDs to Coat Thin Film Cells
  Provided By Industry
• Carry Out Current-Voltage and Photoresponse
  Analyses, Physical Characterization In
  Collaboration With NREL and Modeling to
  Investigate Degradation Mechanisms

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Background

• PNNL Has Developed Multilayer Coatings For
  Organic LEDs
• Multilayers Comprised Of Alternating Polymer
  And Oxide Layers
• Have Demonstrated Coatings On Glass Characterized
  By WVTR Values Less Than 2x10-7 g/m2/d

OLED
Multilayer Coating
Glass
OLED Structure
Cure
Ceramic Deposition
Monomer
WVTR (g/m2/d)
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Basis For Multilayer Coating
H2O Through Defect
Oxide Layer

• Diffusion Rate Of Water And Oxygen Through
  Homogeneous Oxide Layers Is Extremely Low
• Penetration Of Moisture Or Oxygen Through Oxide
  Based Coatings Occurs Because Of Defects In
  Oxide Usually Due To Region Of Substrate
  Protruding Through Coating
• PNNL Approach
• - Smoothing First Polymer Layer
• - Multilayer To Provide Tortuous
• Path For Water And Oxygen

Substrate
Multilayer Coating
Substrate
First Polymer Smoothing Layer
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Barrier Coatings For SSI Circuits

• PNNL Is Collaborating With SSI To Develop Barrier
  Coatings For SSI Circuits
• SSI Provides 10 cm x 10 cm Circuits With Depleted
  Edge
• Multilayer Coatings Applied As Illustrated With
  Relatively Thick First Polymer Layer
• Coated Circuits Subjected To 60ºC/90 RH For
  Accelerated Testing

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Process Development

• Clean Circuits To Eliminate Debris
• Nodules In CIGSS Is Key Issue
• First Layer Adjusted To Achieve Effective Barrier
• Initial Polymer Layer Thickness Was 0.5 µm For
  Coating Shown In Micrographs
• Circuits Coated With First Layer Being 0.5 µm
  Began To Degrade After 600 Hours

5 µm Nodule
12 m Nodule
Potential Pathway
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Process Development

• Micrograph Is For Multilayer
• Coating With Initial Polymer
• Layer Of 4 µm
• Note The Planarizing Effect
• Of First Layer
• Coatings With Initial Layer
• Of 4 µm Allow SSI Circuits
• To Survive 1000 Hours In
• 60ºC/90RH Environment

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Results For SSI Circuits

• SSI Circuits With No Barrier Coating Degrade
  Rapidly In a 60ºC/90 RH Environment
• Developed An Approach For Barrier Coating
  Deposition That Provides Significant Protection
  Less Than 5 Decrease In Efficiency After 1000
  Hours Under 60/90 Conditions
• Thickness Of First Polymer Layer For Results
  Shown Is As Follows
• - Circuit A -- No Barrier Coating
• - Circuit B -- 0.5 µm
• - Circuit C -- 4.0 µm
  

C
B
A
Efficiency vs Hours At 60ºC / 90 RH
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Measurements By Shell Solar

• Two Coated Circuits Were Returned To SSI For
  Characterization
• SSI Measured I-V As Received From PNNL, Then
  Subjected To UV For 10 Days And Tested Again

Circuit Isc (Amps) Voc (Volts) FF
Pmax (Watts) Rel Change
Bare Circuit 22 - 4 0.184
5.633 0.508
0.525 Coated Circuit 22 - 4 0.192
5.420 0.561 0.582
1.108 (1000 hr _at_60/90) After UV
Test 22 - 4 0.183 5.275
0.515 0.498
0.856 Bare Circuit 22 - 9
0.180 5.652 0.581
0.592 Coated Circuit 22 - 9
0.189 5.495 0.608
0.631 1.066 (1000 hr _at_ 60/90) After
UV Test 22 - 9 0.183
5.750 0.653 0.688
1.091
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Measurements By Shell (Continued)
Circuit
Efficiency ()
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Bare Circuit
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22 - 9
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Coated Circuit 1000 Hrs _at_ 60/90
After 10 Days Of UV
22 -4
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Effect Of Moisture On Bare SSI Circuit
mA/cm2
Hrs _at_ 60/90
Hrs _at_ 60/90
Hrs _at_ 60/90
Hrs _at_ 60/60
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Effect Of Moisture On Bare SSI Circuit
Photoresponse And I-V Parameters

• External Photoresponse
• Measurements for Small Cell
• Formed On Rectangular
• Region Cut From SSI Module
• Dark I-V Characteristics
• All of Average Cell
• Parameters Degrade

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Modifed Barrier Coating Structure

• Current Approach
• Multilayer Structure Consists Of
• Initial Polymer Layer /Al2O3
• Plus 4 Pairs Of Polymer/Al2O3
• Layers
• Reduced Number Of Pairs
• Will Utilize Initial Layers, But
• Begin To Reduce Number Of Pairs
• Early Results For Efficiency Of
• Circuit With Three-Pair Coating
• Given In Figure

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• Key Results
• PNNL Multilayer Barrier Coating Developed That
  Effectively Protects SSI Circuits From Moisture
  in 60/90 Environment
• Effects Of Moisture On Uncoated SSI Circuits
  Characterized
• Future Work
• Initiate Testing Of SSI Circuits at 85/85
• Investigate Effects Of Multilayer Coatings With
  Reduced
• Number of layers
• Correlate SSI Circuit With Estimated WVTR Values
• Consider Studies of Other Types Of Cells