Stress Induced Degra

Modes in CIGSS Minim

Mike Kempe

1, Kent Terwilliger

1, and Dale 

1 National Renewable Energy Laboratory (NR

1617 Cole Boulevard, Golden, CO 80401 2 Shell Solar

NREL/PR-520-43310Presented at the 33rd IEEE Photovoltaic Specialist Conference held May 11-16, 20
Experimental Objectiv

 Compare the performance 

exposed to high temperatuhumidity.

 Determine the effects of di

encapsulants on long term CIGSS modules.

 Analyze failure modes to de

areas in need of improvem
Experimental Setup

 Systematically changed:

 (1) Encapsulant (EVA or GE RTV615 silic (2) Front-sheet (Glass or Tefzel)

 Samples exposed to:

 (1) 85C/85% RH in air. (2) 85C/0% RH in air. (Dew point ~ -40

 Used 4 or 5 replicates. 4*2

3+2=34 s

 Initial average cell parameters:

 Voc=0.538 V Jsc=32.8 mA/cm2 FF=65.7%

η=11.59% 
Stress at 85°C and 85% 

Causes Rapid Degradat

300200100

0

-100-200-300

Current (mA)

-4 -2 0 2 4 6 8 10

Voltage (V)

 Shell Solar CIGSS #32  Laminated with GE RTV615  Dow Corning 1200 Primer Tefzel Frontsheet Stressed at 85oC/85% RH

 0 h

 1 h 103 h 199 h 457 h

-300-200-100

0

100200300

Current (mA)

-4 -2 

 Shell Solar CIGS Laminated with E Glass Frontsheet Stressed at 85oC

 0 h

 1 h 103 h 199 h 457 h 935 h

Silicone with Tefzel Front-Sheet EVA with 

Glass Slows down the degradation but does 
Infrared Images Show

Striped Pattern

+81 mA, 9.6 

Forward B

Silicone encapsulant with a Tefzel Front-Sheet

457 h of 85 oC and 85% RH

-0.24 mA, -9.6 V

Reverse Bias

No Signs of Shunts
IR Heat Pattern Indic

Resistance ZnO

Warmer

Area

IR image of module under forward bias of 9.6V and 81 mA.

Schematic representation of Cinterconnection scheme

Heating not symmetric arouand therefore is not due to rinterconnection scribes.

P1 P2 P3 
Heating Caused Princ

Recombination Curre

⎥⎥⎦⎤

⎢⎢⎣⎡

=

−

⎟⎠⎞ ⎜

⎝⎛

1exp nkT

qV

ojj

0

0.10.20.30.40.50.6

0 0.2 0.4 0.6 0.8 1

Distance Across Cell

Absorber Voltage Drop 

0123456789

Current Density Through 

the Absorber

P1 P2 P3 P1 P2 
85°C and 0% RH Expos

Causes Voc and FF Loss

400200

0

-200

Current (mA/cm

2

)

-4 -2 0 

 Shell Solar CIGSS # Laminated with EVA  Glass Frontsheet Stressed at 85oC/0% 

 0 h

 1 h 103 h 199 h 457 h 935 h 1574 h 2287 h 3607 h 4663 h 6463 h 8767 h

600500400300200100

0

-100-200-300

Current (mA)

-4 -2 0 2 4 6 8 10

Voltage (V)

 Shell Solar CIGSS #29  Laminated with GE RTV615  Dow Corning 1200 Primer  Tefzel Frontsheet Stressed at 85oC/0% RH

 0 h

 1 h 103 h 199 h 457 h 935 h 1574 h 2287 h 3607 h 4663 h 6463 h 8767 h

Silcone 

Silicone encapsulated cells performed better. They had better fill fa
An Analysis of Variance 

Statistical Significance

Two factor ANOVA for samples exposed to 8767 h of 85oC and 0% “F ratio” is the ratio of the uncertainty between treatments to the sa“Probability” is the chance of getting this F ratio if the two treatmen

“Encapsulant*Front-sheet” indicates the probability that intera

significantly affect the results. 

Resistances determined from inverse s
Silicone Encapsulated C

Lower FF and “R

s“ Loss

Resistances were inferred from the inverse slope. The horizontal lines for each data set correspond to the 95% confidence intervaThe large horizontal line spanning the plots is the grand mean for the data set. 

Efficiency Change

-6-5-4-3-2-1

0

E/G E/T Si/G Si/T

FF Change

-25-20-15-10

-5

0

E/G E/

Rseries,light Change

05

101520

E/G E/T Si/G Si/T

Rshunt,dark Change

0

50000

100000150000

E/G E/T 

8767 hours of 85oC and 0% RH
At 8767 h 85C and 0% 

ZnO Resistance Has I

Forward Bias Module #159.5 V, 31 mA, 15 s8767 h 85

°C and 0% RH

EVA/Tefzel

Rseries,light Change (ohm)

05

101520

E/G E
IR Images Distinguish 

Diodes from Shunts

5 s forward Bias9.3 V 153 mA

Silicone/Tefzel after 2290 h 85oC and 0% R

5 s Reverse Bias9.3 V 0.53 mA

IR images are made by subtracting image values before and af
Many Weak Diodes A

Located on the P1 sc

Flashlight Illumination

The flashlight illuminated the side of the cell just outside the image to ensure that we were not just seeing a reflection.

P

Silicone/Tefzel after 2290 h 85oC and 0% RH. 
Weak Diodes Principally 

at P1 Scribes or Cell Ed

Weak-diode P1 Weak-diode Cell

Weak-diode Edge
The Number of Weak 

Barely Changed

Module #30, Silicone/Tefzel at 85

°C/0% RH

Reverse Bias Forward Bia

2.3 mA, -9.5V20s8770 h Exposure

Shunts Shunts and Weak 

2 mA, -9.6V20s2290 h Exposure
Diodes are Weaker b

Shunting is Unchange

Voc Change per Cell (V)

-0.045

-0.04

-0.035

-0.03

-0.025

-0.02

-0.015

-0.01

-0.005

0

E/G E/T Si/G Si/T

8770 h exposure to 85

°C and 0% RH

Rshunt,Light Change Module (ohm) -2000 -1500 -1000 -500

0

500

1000

E/G 

Voc

R

Similar change in Voc across all sample sets. No statistically sig
Conclusions

 Exposure to 85°C and 85% RH for 4

 Large increases in ZnO resistance. Some Voc losses.

 Exposure to 85°C and 0% RH for 87

 Small increases in ZnO resistance. Some Voc losses. No shunting change. Silicone encapsulated cells performed  EVA produced greater losses in FF and 
Acknowledgements

 The authors would like to t

McMahon for helping with timaging and David Albin focomputer code. 

 This work was supported b

Department of Energy undNo. DE-AC36-99GO10337 wNational Renewable Energy