Reliability Concerns Associated with PV Technologies
Nick Bosco National Renewable Energy Laboratory 1617 Cole Blvd. Golden, CO 80401 303.384.6337
[email protected]
This document is a non-comprehensive summary of known reliability concerns for PV technologies. It has 3 parts: 1. List of reliability concerns with corresponding references 2. Reference list 3. Prioritization of failures
If you have comments about changes needed to this document or about the value of this summary, please send these to
[email protected]. If this type of information is found to be useful to the community, we will update it periodically.
1.0 Wafer Silicon 1.1 Cracked cells (bonding processes, strain, etc.) [1-4] 1.2 Solder joint or gridline interface failure (increased series resistance) [5] 1.3 Reduced adhesion leading to corrosion and/ or delamination [6, 7] 1.4 Slow degradation of ISC [8] 1.5 Fatigue of ribbon interconnect 1.6 Junction box failure (poor solder joints, arcing, etc.) [9] 1.7 Busbar adhesion degradation, electrical contact, etc. 1.8 Glass edge damage of frameless modules (though installation, handling, etc.) 1.9 Light-induced cell degradation 1.10 Effect of glass on encapsulant performance [10-13] 1.11 Front surface soiling [14] 1.12 Mechanical failure of glass-glass laminates [14] 1.13 General issues [section 7.0] 2.0 Thin Film Silicon 2.1 Electrochemical corrosion of SnO2:F [15-17] 2.2 Initial light degradation (a-Si) [18-22] 2.3 Annealing instabilities (a-Si) [23, 24] 2.4 General issues [section 7.0] CdTe 3.1 Cell layer integrity- back contact stability [25] 3.2 Cell layer integrity- interlayer adhesion and delamination; electrochemical corrosion of SnO2:F [15-17, 26] 1
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3.0
3.3 Fill-factor loss (increased series resistance and/ or recombination) [27] 3.4 Busbar adhesion degradation, electrical contact, etc. [28] 3.5 Shunt hot spots at scribe lines before and after stress [25] 3.6 Weak diodes, hot spots, nonuniformities before and after stress 3.7 General issues [section 7.0] 4.0 CIS 4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8
Cell layer integrity – contact stability Cell layer integrity – interlayer adhesion Fill-factor loss (increased series resistance and/or recombination) [29-33] Busbar failure – mechanical (adhesion) and electrical Notable sensitivity of TCO to moisture [34] Moisture ingress failure of package [29, 34, 35] Cell–to-cell interconnect (discrete cells) Notable sensitivity of TCO to moisture; need to pass damp heat test (nonshingle specific)[34] 4.8 Shunt hot spots at scribe lines before and after stress [30] 4.9 Weak diodes, hot spots, nonuniformities before and after stress 4.10 Edge shunting 4.11 General issues [section 7.0]
5.0 OPV 5.1 5.2 5.3 5.4 5.5 5.6 5.7 6.0 CPV 6.1 6.2 6.3 6.4 6.5 6.6 6.7 6.8
Delamination of layers [36, 37] Photolytic Instability [38] Moisture induced degradation [39] Moisture ingress failure of package [40, 41] O2 induced degradation [36, 37] Thermal instability of donors and acceptors General issues [section 7.0]
Depolymerization, bubble formation, and yellowing of silicone encapsulants under high flux and high temperature with thermal cycling for long periods of time [42] Soiling and delamination of anti reflective coatings on internal optical components Cell damage from thermal runaway (may be caused by solder voids?) Loss of efficiency of optics [42] Poor solder joints between string ribbons and wires inside junction boxes – arcing Potential issues with highly non-uniform illumination Defect migration, …(especially for lattice mismatched) Corrosion and diffusion of silver gridlines/contacts 2
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6.9 6.10 6.11 6.12 6.13 6.14
Electromigration due to high current under high concentration (tunnel junction) Inverter reliability (ability to withstand rapid changes in current) Module thermal fatigue (including high frequency and amplitude), materials, interconnects, cell attachment, adhesive failure [43] Operational integrity of the mechanical parts of the trackers (for high concentration systems) High Al content AlInP can be sensitive to oxidation [44] General issues [section 7.0]
7.0 General Issues Across all Technologies 7.1 Corrosion leading to loss of grounding [45, 46] 7.2 Quick connector reliability 7.3 Improper insulation leading to loss of grounding [47-49] 7.4 Delamination [7, 25, 50, 51] 7.5 Glass fracture [52] 7.6 Bypass diode failure [53] 7.7 Inverter reliability 7.8 Moisture ingress [40, 41]
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Reference list
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World Conference on PV Energy Conversion, Waikoloa, Hawaii, USA, 1994, pp. 893-896. R. G. Ross, "Crystalline-silicon reliability lessons for thin-film modules," in Proceedings of the 18th IEEE PV Specialists Conference, Las Vegas, Nevada, USA, 1985, pp. 1014-1020. K. W. Jansen and A. E. Delahoy, "A laboratory technique for the evaluation of electrochemical transparent conductive oxide delamination from glass substrates," Thin Solid Films, vol. 423, pp. 153-160, 2003.http://www.sciencedirect.com/science/article/B6TW0-47F7C5R3/1/652ab45b14688bac1db42d01f4b7d4f9 G. Mon, L. Wen, J. Meyer, R. Ross, Jr., and A. Nelson, "Electrochemical and galvanic corrosion effects in thin-film photovoltaic modules," in Photovoltaic Specialists Conference, 1988., Conference Record of the Twentieth IEEE, 1988, pp. 108-113 vol.1. C. R. Osterwald, T. J. McMahon, and J. A. del Cueto, "Electrochemical corrosion of SnO2:F transparent conducting layers in thin-film photovoltaic modules," Solar Energy Materials & Solar Cells, vol. 79, pp. 21-33, 2003 F. H. Klotz, G. Massano, A. Sarno, and L. Zavarese, "Determination and analysis of the performance and degradation of a-Si modules using outdoor, simulator and open-circuit-voltage-decay (OCVD) measurements," in Proceedings of the 8th European Commission PV Solar Energy Conference, Florence, Italy, 1988, pp. 499-503. P. Ragot, R. Berre, D. Desmettre, P. Paes, and D. Royer, "Laboratory and field testing of amorphous silicon modules and arrays," in Proceedings of the 8th European Commission PV Solar Energy Conference, Florence, Italy, 1988, pp. 79-83. T. Yoshida, K. Maruyama, O. Nabeta, Y. Ichikawa, H. Sakai, and Y. Uchida, "High efficiency a-Si:H two-stacked tandem solar cell," in Proceedings of the 19th IEEE PV Specialists Conference, New Orleans, Louisiana, USA, 1987, pp. 1095-1100. D. Cunningham and J. Morris, "The use of indoor light soak data to project end of life output power of hydrogenated amorphous silicon solar modules," in SERI/DOE Photovoltaic Module Reliability Workshop, SERI/CP-213-3553 DE1002120, Lakewood, Colorado, USA, 1990, pp. 79-94. J. Newton, "Comparison of amorphous silicon degradation under various light sources," in NREL/DOE Photovoltaic Performance and Reliability Workshop, SERI/CP-411-5184 DE93000017, Golden, Colorado, USA, 1992, pp. 123-136. N. Vela, F. Fabero, and F. Chenlo, "Testing of stability and reliability of a-Si PV modules: long term life time prediction," in Proceedings of the 12th European PV Solar Energy Conference, Amsterdam, The Netherlands, 1994, pp. 1210-1213. R. DeBlasio, L. Mrig, and D. Waddington, "Interim qualification tests and procedures for terrestrial photovoltaic thin-film flate-plate modules," in Proceedings of the 22nd IEEE PV Specialists Conference, Las Vegas, Florida, USA, 1991, pp. 796-801.
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T. J. McMahon, "Accelerated testing and failure of thin-film PV modules," Progress in Photovoltaics, vol. 12, pp. 235-248, Mar-May 2004.<Go to ISI>://CCC:000220731200009 J. Ermer, C. Fredric, J. Hummel, C. Jensen, D. Pier, D. Tarrant, and K. Mitchell, "Advances in large area CuInSe2 thin film modules," in Proceedings of the 21st IEEE PV Specialists Conference, Kissimimee, Florida, USA, 1990, pp. 595-599. D. E. Tarrant, A. R. Ramos, S. R. Willett, and R. R. Gay, "CuInSe2 module environmental durability," in Proceedings of the 22nd IEEE PV Specialists Conference, Las Vegas, Florida, USA, 1991, pp. 553-556. T. J. McMahon and G. J. Jorgensen, "Progress toward a CdTe cell life prediction," AIP Conference Proceedings ; VOL. 462 ; ISSUE: 1 ; 15. National Center for Photovoltaics program review conference, Denver, CO (United States), 9-11 Sep 1998 ; PBD: Mar 1999, pp. pp. 54-61 ; PL:, 1999 D. Willett, "Environmental testing of CIS based modules," in NREL/DOE Photovoltaic Performance and Reliability Workshop, NREL/CP-411-20379 DE96000468, Golden, Colorado, USA, 1995, pp. 25-36. J. Wennerberg, J. Kessler, and L. Stolt, "Degradation mechanisms of Cu(In,Ga)Se2-based thin film PV modules," in Proceedings of the 16th European PV Solar Energy Conference, Glasgow, UK, 2000, pp. 309-312. J. Wennerberg, J. Kessler, M. Bodergard, and L. Stolt, "Damp heat testing of high performance CIGS thin film solar cells," in Proceedings of the 2nd World Conference and Exhibition on Photovoltaic Solar Energy Conversion, Vienna, Austria, 1998, pp. 1161-1164. J. Wennerberg, J. Kessler, and L. Stolt, "Cu(In,Ga)Se2-based thin-film photovoltaic modules optimized for long-term performance," Solar Energy Materials & Solar Cells, vol. 75, pp. 47-55, 2003 T. Yanagisawa and T. Kojima, "Behavior of a CuInSe2 solar module under light irradiation in light/dark cycle tests," Solar Energy Materials & Solar Cells, vol. 77, pp. 83-87, 2003 C. Heske, G. Richter, Z. Chen, R. Fink, and E. Umbach, "Influence of humidity on polycrystalline Cu(In,Ga)Se2 thin films for solar cells: a study of Na and H2O coadsorption," in Proceedings of the 25th IEEE PV Specialists Conference, Washington, DC, USA, 1996, pp. 861-864. D. H. Otth and R. G. Ross, "Assessing photovoltaic module degradation and lifetime from long-term environmental tests," in Proceedings of the 29th Institute of Environmental Sciences Technical Meeting, Los Angeles, California, USA, 1983, pp. 121-126. M. O. Reese, A. J. Morfa, M. S. White, N. Kopidakis, S. E. Shaheen, G. Rumbles, and D. S. Ginley, "Pathways for the degradation of organic photovoltaic P3HT : PCBM based devices," Solar Energy Materials and Solar Cells, vol. 92, pp. 746752, Jul 2008.<Go to ISI>://000256121300007 S. E. Shaheen, "Mechanisms of operation and degradation in solution-processable organic photovoltaics," in 2007 IEEE International Reliability Physics Symposium Proceedings, Phoenix, AZ, USA, 2007, pp. 5 pp.-5 pp. M. O. Reese, N. Kopidakis, G. Rumbles, D. S. Ginley, A. J. Morfa, M. S. White, and S. E. Shaheen, "Short-Term Metal/Organic Interface Stability Invesitgations 6
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of Organic Photovoltaic Devices," 33rd IEEE Photovoltaic Specialist Conference Program, 2008 K. Kawano, R. Pacios, D. Poplavskyy, J. Nelson, D. D. C. Bradley, and J. R. Durrant, "Degradation of organic solar cells due to air exposure," Solar Energy Materials and Solar Cells, vol. 90, pp. 3520-3530, 2006.http://www.sciencedirect.com/science/article/B6V51-4KJ0SMX5/2/928503224ed44939997b0ab65dfee090 D. H. Otth and R. G. Ross, "Assessing photovoltaic module degradation and lifetime from long-term environmental tests," in Proceedings of the 30th Institute of Environmental Sciences Technical Meeting, Los Angeles, California, USA, 1984, pp. 121-126. G. Mon, L. Wen, and R. Ross, "Encapsulant free-surfaces and interfaces: critical parameters in controlling cell corrosion," in Proceedings of the 19th IEEE PV Specialists Conference, New Orleans, Louisiana, USA, 1987, pp. 1215-1221. K. Araki, H. Uozumi, T. Egami, M. Hiramatsu, Y. Miyazaki, Y. Kemmoku, A. Akisawa, N. J. Ekins-Daukes, H. S. Lee, and M. Yamaguchi, "Development of concentrator modules with dome-shaped Fresnel lenses and triple-junction concentrator cells," Progress in Photovoltaics: Research and Applications, vol. 13, pp. 513-527, 2005.http://dx.doi.org/10.1002/pip.643 M. Cao, S. Butler, J. T. Benoit, Y. Jiang, R. Radhakrishnan, Y. Chen, S. Bendapudi, and S. Horne, "Thermal stress analysis/life prediction of concentrating photovoltaic module," Journal of Solar Energy EngineeringTransactions of the Asme, vol. 130, p. 9, May 2008.<Go to ISI>://000255839800011 A. W. B. S. van Riesen, "Degradation study of III-V solar cells for concentrator applications," Progress in Photovoltaics: Research and Applications, vol. 13, pp. 369-380, 2005.http://dx.doi.org/10.1002/pip.603 S. N. Labs, "http://photovoltaics.sandia.gov/docs/installation.html#AnchorGround," Photovolatic Systems Research and Development A. Levins and R. S. Sugimura, "Photovoltaic array grounding and electrical safety," United States, 1982, pp. Pages: 1061-1066. R. S. Sugimura, G. R. Mon, L. Wen, and R. G. Ross, "Electrical isolation design and electrochemical corrosion in thin-film photovoltaic modules," in Proceedings of the 20th IEEE PV Specialists Conference, Las Vegas, Nevada, USA, 1988, pp. 1103-1109. R. S. Sugimura, L. C. Wen, G. R. Mon, and R. G. Ross, "Test techniques for voltage/humidity-induced degradation of thin-film photovoltaic modules," in SERI/DOE Photovoltaic Module Reliability Workshop, SERI/CP-213-3553 DE89009459, Lakewood, Colorado, USA, 1989, pp. 29-50. G. R. Mon and R. G. Ross, "Electrochemical degradation of amorphous-silicon photovoltaic modules," in Proceedings of the 18th IEEE PV Specialists Conference, Las Vegas, Nevada, USA, 1985, pp. 1142-1149. D. L. King, M. A. Quintana, J. A. Kratochvil, D. E. Ellibee, and B. R. Hansen, "Photovoltaic module performance and durability following long-term field 7
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exposure," Progress in Photovoltaics: Research Applications, vol. 8, pp. 241-256, 2000 G. J. Jorgensen and T. J. McMahon, "Accelerated and outdoor aging effects on photovoltaic module interfacial adhesion properties," Progress in Photovoltaics: Research Applications, vol. 16, pp. 187-196, 2008 M. A. Quintana, D. L. King, F. M. Hosking, J. A. Kratochvil, R. W. Johnson, and B. R. Hansen, "Diagnostic analysis of silicon photovoltaic modules after 20-year field exposure," in Proceedings of the 28th IEEE PV Specialists Conference, Anchorage, Alaska, USA, 2000, pp. 1420-1423. M. I. Smokler, D. H. Otth, and R. G. Ross, "The Block program approach to photovoltaic module development," in Proceedings of the 18th IEEE PV Specialists Conference, Las Vegas, Nevada, USA, 1985, pp. 1150-1158.
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Reliability Concerns Associated with Application of PV Technologies in Systems
Known and Anticipated Failure Modes & Degradation Mechanisms Priority/Prob. of Success / Role for Labs (High-MediumLow) H/H/H H/H/L H/H/L H/M/M M/H/L M/H/L M/H/M H/H/H H/M/H H/M/M M/M/M M/M/M H/H/L H/M/L M/M/M M/M/L M/M/L M/M/L M/M/L L/M/L L/H/L M/M/L L/L/L Light soaking; Voltage biased damp heat 2 Light soaking Diagnostic Technique / Qual Test (e.g., chamber tests, HVTB) Comment
Corrosion leading to loss of grounding Quick connector reliability Improper installation leading to loss of grounding Delamination Glass breakage Bypass diode failure Inverter reliability Poor solder joints between string ribbons and wires inside junction boxes – arcing Cracked cells (caused by bonding of conductors, strain etc.) Increased series resistance from solder joint or gridline interface failure Reduced adhesion strength that increases corrosion and/or delamination Slow degradation of Isc Fatigue of ribbon due to thermal cycling Junction box failure Busbar adhesion, electrical contact, etc. Glass edge damage of frameless modules (installation, handling, etc.) Light-induced cell degradation Effect of glass on encapsulant durability Effect of glass on module performance Front surface soiling Stress breakage in glass-glass laminates
General
This is especially a problem for flexible packages For products using glass
Electroluminescence can detect cracks. 1
Cracking may become worse for thinner wafers This is not new, but continues to be a quality assurance issue Mechanisms are not fully understood Not new, but continues to be an issue Frameless construction is infrequently used today for Si. Problems may return because of Ce being removed from the glass Glass-glass laminates are almost never used because of added weight.
Wafer Si Film Si
See items listed in “General” section Electrochemical corrosion of SnO2:F Initial light degradation (a-Si)
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Annealing instabilities (a-Si) Cell layer integrity – backcontact stability Cell layer integrity – interlayer adhesion and delamination; Electrochemical corrosion of SnO2:F Fill-factor loss (increased series resistance and/or recombination) Busbar failure - mechanical (adhesion) and electrical Shunt hot spots at scribe lines before and after stress Weak diodes, hot spots, nonuniformities before and after stress Cell layer integrity – contact stability Cell layer integrity – interlayer adhesion Fill-factor loss (increased series resistance and/or recombination) Busbar failure – mechanical (adhesion) and electrical Notable sensitivity of TCO to moisture Moisture ingress failure of package Cell–to-cell interconnect (discrete cells) Notable sensitivity of TCO to moisture; need to pass damp heat test (non-shingle specific) Shunt hot spots at scribe lines before and after stress Weak diodes, hot spots, nonuniformities before and after stress Edge shunting Delamination of layers
L/L/L H/H/H L/L/M H/M/H H/H/M H/M/M H/M/H H/H/H M/H/M H/M/H M/H/M H/M/H H/M/H H/M/H H/M/M H/M/M H/M/H M/H/M H/M/H H/M/H H/L/H H/L/H
Light soaking Voltage biased damp heat2 Cell + Module Light soaking; Damp Heat IR Camera; Hot/humid vs. damp heat IR Camera; Hot/humid vs. damp heat IR Camera; Hot/humid vs. damp heat Screen at cell initially; then module Thermal stress 3
CdTe
Mo backcontact (all), the front contact is only a problem when the module is assembled from discrete cells Cell + Module Light soaking; Damp Heat IR Camera; Hot/humid vs. damp heat Damp heat exposure Hot/humid vs. damp heat IR Camera; Hot/humid vs. damp heat Damp heat exposure IR Camera; Hot/humid vs. damp heat IR Camera; Hot/humid vs. damp heat Screen at cell initially; then module
Flexible roofing products Flexible roofing products; this is a problem when discrete devices are interconnected into modules
CIS
Discrete Cell – Flexible roofing products
OPV
Photolytic Instability Moisture induced degradation Moisture ingress failure of package
We note that OPV technology is not yet well understood and this section may change substantially. Currently, samples are usually handled within a glove box because of sensitivity to air.
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O2 induced degradation Thermal instability of donors and acceptors Depolymerization, bubble formation, and yellowing of silicone encapsulants under high flux and high temperature with thermal cycling for long periods of time. Soiling and delamination of anti reflective coatings on internal optical components. Cell damage from thermal runaway (may be caused by solder voids?) Loss of efficiency of optics. Poor solder joints between string ribbons and wires inside junction boxes – arcing Potential issues with highly non-uniform illumination. Defect migration, …(especially for lattice mismatched) Corrosion and diffusion of silver gridlines/contacts Electromigration due to high current under high concentration (tunnel junction) Inverter reliability (ability to withstand rapid changes in current) Module thermal fatigue (including high frequency and amplitude), materials, interconnects, cell attachment, adhesive failure Operational integrity of the mechanical parts of the trackers (for high concentration systems) High Al content AlInP can be sensitive to oxidation
H/L/H H/L/H H/H/H UV exposure with T control? A new technique is needed. Bubble formation has been observed in the field.
M/H/M H/H/H H/H/H M/M/L H/H/M M/M/M M/H/M M/H/H M/M/M H/H/L Ultrasonic test after thermal cycling. Test is controversial Has been known for some time, but is still a problem Collaboration with CSP
This issue has not yet been adequately assessed. Relevance of 1000 hours in damp heat has not been established in the field Severity of problem has not been assessed The special challenges of designing an inverter for CPV have not been assessed Adhesives need to be tested from multiple perspectives. The issues with handling inverted cells off of their original substrates is not yet well understood Use Pb-containing solders, or confirm that Pb-free solders have needed longevity in tracker controllers.
CPV
H/H/M M/M/M
1
“The Effect of Cell Thickness on Module Reliability”, J. H. Wohlgemuth, D. W. Cunnigham, N. V. Placer, G. J. Kelly, A. M. Nguyen, 33rd IEEE, San Diego, CA 2008. 2 “A Laboratory Technique for the Evaluation of Electrochemical Transparent Conductive Oxide Delamination from Glass Substrates”, Jansen and Delahoy, 2003. 3 “Progress Toward a CdTe Cell Life Prediction”, McMahon and Jorgensen, 1999.
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