Dr. F. J. John Pern Profile

Dr. F. J. John Pern

at Sunshine Sci-Tech LLC

SPIE Involvement:

Author

Area of Expertise:

Chemical Instrumental Analysis , Photovoltaic Module Encapsulation , PV Performance Reliability , Materials Science , Thin film CIGS Solar Cells , Solar Energy

Websites:

Company Website

A senior scientist with NCPV at NREL for over 25 years. Research experience includes photo-/electrochemistry on water splitting, electrodepostion of thin fim CuInSe2 for solar cells and precursors of high Tc superconductor, synthesis of fuel cell proton membranes, Formulation and accelerated tests of PV module encapsulants and module performance relaibility, and thin film CuInGaSe2 solar cell reliability.

Proceedings Article | 16 October 2012 Paper

Investigation of some transparent metal oxides as damp heat protective coating for CIGS solar cells

F. J. Pern, F. Yan, K. Zaunbrecher, B. To, J. Perkins, R. Noufi

Proceedings Volume 8472, 84720I (2012) https://doi.org/10.1117/12.930539

KEYWORDS: Copper indium gallium selenide, Solar cells, Atomic layer deposition, Zinc oxide, External quantum efficiency, Glasses, Time multiplexed optical shutter, Coating, Electroluminescence, Quantum efficiency

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Proceedings Article | 16 October 2012 Paper

Stability of CIGS solar cells and component materials evaluated by a step-stress accelerated degradation test method

F. J. Pern, R. Noufi

Proceedings Volume 8472, 84720J (2012) https://doi.org/10.1117/12.930541

KEYWORDS: Copper indium gallium selenide, Resistance, Solar cells, Nickel, Molybdenum, Zinc oxide, Capacitance, Glasses, Capacitors, Photography

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A step-stress accelerated degradation testing (SSADT) method was employed for the first time to evaluate the stability of CuInGaSe₂ (CIGS) solar cells and device component materials in four Al-framed test structures encapsulated with an edge sealant and three kinds of backsheet or moisture barrier film for moisture ingress control. The SSADT exposure used a 15°C and then a 15% relative humidity (RH) increment step, beginning from 40°C/40%RH (T/RH = 40/40) to 85°C/70%RH (85/70) as of the moment. The voluminous data acquired and processed as of total DH = 3956 h with 85/70 = 704 h produced the following results. The best CIGS solar cells in sample Set-1 with a moisture-permeable TPT backsheet showed essentially identical I-V degradation trend regardless of the Al-doped ZnO (AZO) layer thickness ranging from standard 0.12 μm to 0.50 μm on the cells. No clear “stepwise” feature in the I-V parameter degradation curves corresponding to the SSADT T/RH/time profile was observed. Irregularity in I-V performance degradation pattern was observed with some cells showing early degradation at low T/RH < 55/55 and some showing large Voc, FF, and efficiency degradation due to increased series Rs (ohm-cm²) at T/RH ≥ 70/70. Results of (electrochemical) impedance spectroscopy (ECIS) analysis indicate degradation of the CIGS solar cells corresponded to increased series resistance Rs (ohm) and degraded parallel (minority carrier diffusion/recombination) resistance Rp, capacitance C, overall time constant Rp*C, and “capacitor quality” factor (CPE-P), which were related to the cells’ p-n junction properties. Heating at 85/70 appeared to benefit the CIGS solar cells as indicated by the largely recovered CPE-P factor. Device component materials, Mo on soda lime glass (Mo/SLG), bilayer ZnO (BZO), AlNi grid contact, and CdS/CIGS/Mo/SLG in test structures with TPT showed notable to significant degradation at T/RH ≥ 70/70. At T/RH = 85/70, substantial blistering of BZO layers on CIGS cell pieces was observed that was not seen on BZO/glass, and a CdS/CIGS sample displayed a small darkening and then flaking feature. Additionally, standard AlNi grid contact was less stable than thin Ni grid contact at T/RH ≥ 70/70. The edge sealant and moisture-blocking films were effective to block moisture ingress, as evidenced by the good stability of most CIGS solar cells and device components at T/RH = 85/70 for 704 h, and by preservation of the initial blue color on the RH indicator strips. The SSADT experiment is ongoing to be completed at T/RH = 85/85.

Proceedings Article | 13 September 2011 Paper

Characterization of damp heat degradation of CuInGaSe2 solar cell components and devices by (electrochemical) impedance spectroscopy

F. J. John Pern, Rommel Noufi

Proceedings Volume 8112, 81120S (2011) https://doi.org/10.1117/12.895918

KEYWORDS: Resistance, Copper indium gallium selenide, Solar cells, Gold, Capacitors, Molybdenum, Glasses, Nickel, Silver, Zinc oxide

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This work evaluated the capability of (electrochemical) impedance spectroscopy (IS, or ECIS as used here) to monitor damp heat (DH) stability of contact materials, CuInGaSe2 (CIGS) solar cell components, and devices. Cell characteristics and its variation of the CIGS devices were also examined by the ECIS. Bare and encapsulated sample sets were separately prepared and exposed in an environmental chamber at 85°C and 85% relative humidity (RH). The ECIS results from bare samples tested within 50-100 h of DH exposure allowed the determination of the use of a conducting Ag paste and a low-melting-point solder alloy for making a DH-stable external connection with Au wires. Bare Mo and AlNi grid degraded (corroded) rapidly while Ni was DH-stable. The moisture-dampened Al-doped ZnO (AZO) and bilayer ZnO (BZO) likely underwent hydrolytic "capacitor-forming" reaction by DH, resulting in "transient" behavior of very high resistance in ECIS that was not detected by four-point probe. Using an encapsulation test structure that allowed moisture ingress control, DH-induced degradation (resistance increase) rates of BZO on glass decreased from 0.21 ohm/h using a moisture-permeable Tedlar/Polyester/Tedlar (TPT) backsheet to 1.0 x 10^-3 ohm/h using a moisture barrier FG-200 film, while Mo on glass did not exhibit the same conducting degradation and corrosion as the bare samples after over 1270 h DH exposure. CIGS solar cells encapsulated with a TPT backsheet degraded irregularly over 774 h DH exposure. Key resistance and capacitance parameters extracted by curve fitting of impedance data clearly showed the variation and impact of DH exposure on cell characteristics. Profound "depression" or shorting of the "p-n junction capacitor" by DH was evident. ECIS results are shown to correlate reasonably well with the solar cells' currentvoltage (I-V) degrading trends. Furthermore, ECIS analysis was capable of differentiating cell degradation due to "junction capacitor" shorting, damage or breakdown from that due to electrical conduction failure on AlNi/BZO layers.

Proceedings Article | 30 August 2010 Paper

Preliminary damp-heat stability studies of encapsulated CIGS solar cells

R. Sundaramoorthy, F. J. Pern, T. Gessert

Proceedings Volume 7773, 77730Q (2010) https://doi.org/10.1117/12.863076

KEYWORDS: Copper indium gallium selenide, Glasses, Humidity, Solar cells, Reliability, Molybdenum, Resistance, Photovoltaics, Zinc oxide, Aluminum

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Proceedings Article | 19 August 2010 Paper

Variations in damp heat-induced degradation behavior of sputtered ZnO window layer for CIGS solar cells

F. J. Pern, B. To, S. Glick, R. Sundaramoorthy, C. DeHart, S. Glynn, C. Perkins, L. Mansfield, T. Gessert

Proceedings Volume 7773, 77730R (2010) https://doi.org/10.1117/12.863078

KEYWORDS: Zinc oxide, Copper indium gallium selenide, Solar cells, Glasses, Transmittance, Particles, Scanning electron microscopy, Resistance, Crystals, Reliability

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Proceedings Article | 2 September 2009 Paper

Stability of TCO window layers for thin-film CIGS solar cells upon damp heat exposures: part II

R. Sundaramoorthy, F. Pern, C. DeHart, T. Gennett, F. Y. Meng, M. Contreras, T. Gessert

Proceedings Volume 7412, 74120J (2009) https://doi.org/10.1117/12.826604

KEYWORDS: Transparent conductors, Zinc oxide, Absorption, Resistance, Copper indium gallium selenide, Transmittance, Reflectivity, Solar cells, Glasses, Thin films

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Proceedings Article | 2 September 2009 Paper

Stability of TCO window layers for thin-film CIGS solar cells upon damp heat exposures: part III

F. Pern, S. Glick, X. Li, C. DeHart, T. Gennett, M. Contreras, T. Gessert

Proceedings Volume 7412, 74120K (2009) https://doi.org/10.1117/12.826559

KEYWORDS: Zinc oxide, Glasses, Resistance, Thin films, Copper indium gallium selenide, Solar cells, Transmittance, Transparent conductors, Absorption, Photovoltaics

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Various transparent conducting oxide (TCO) films are used as window layers to permit light transmission, photocurrent generation, and for electrical current collection in thin-film photovoltaic technologies. Bilayer composites (BZO) of intrinsic ZnO (i-ZnO) and Al-doped ZnO (AZO) have been used on NREL's high-efficiency CuInGaSe₂ (CIGS) solar cells. Previously, we demonstrated that, when tested in damp heat (DH) condition at 85°C and 85% relative humidity (RH), the stability trend of some TCOs was in decreasing order of SnO₂:F > In₂O₃:SnO₂ (ITO) > ZnO-based films of AZO, BZO and Al-doped Zn_1-xMg_xO (ZMO). We also observed that the degradation rate of AZO, BZO, and ZMO was influenced by additional factors such as film thickness, deposition conditions, and exposure history. This work continued our efforts in searching for a high-performance and high-stability window layer TCO, as well as in finding mitigation methods to protect the ZnO layer, either i-ZnO or BZO, for use on the CIGS solar cells. The current study, which involved the third experimental set of TCOs deposited on glass, further examined in DH test conditions the thickness effect on single-layer AZO films, the glass substrate effect on BZO, the stability and protective effect of amorphous In₂O₃:ZnO (InZnO or IZO) as a conducting window layer for the underlying i-ZnO, and the stability and protective power of a protective transparent metal oxide (PTMO) coating for all three types of ZnO (AZO, BZO, and i-ZnO). The samples were periodically characterized with optical, electrical, and structural measurements during the course of DH exposure. The results show that the DH stability of AZO increased as the film thickness increased, BZO on Corning^® Eagle 2000™ glass degraded somehow faster than on Corning^® 7059™, and both the IZO and PTMO showed generally high DH stability and good protective power for the ZnO layers underneath. However, the results of decreased (002) peak intensity of ZnO from X-ray diffraction analysis indicated that both IZO and PTMO still allowed certain levels of moisture penetration.

Proceedings Article | 10 September 2008 Paper

Degradation of ZnO-based window layers for thin-film CIGS by accelerated stress exposures

F. Pern, R. Noufi, B. To, C. DeHart, X. Li, S. Glick

Proceedings Volume 7048, 70480P (2008) https://doi.org/10.1117/12.795097

KEYWORDS: Zinc oxide, Copper indium gallium selenide, Solar cells, Thin films, Glasses, Coating, Transmittance, Resistance, Reflectivity, Scanning electron microscopy

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Showing 5 of 8 publications

Conference Committee Involvement (10)

Reliability of Photovoltaic Cells, Modules, Components, and Systems X

6 August 2017 | San Diego, California, United States

Reliability of Photovoltaic Cells, Modules, Components, and Systems IX

28 August 2016 | San Diego, California, United States

Reliability of Photovoltaic Cells, Modules, Components, and Systems VIII

9 August 2015 | San Diego, California, United States

Reliability of Photovoltaic Cells, Modules, Components, and Systems VII

20 August 2014 | San Diego, California, United States

Reliability of Photovoltaic Cells, Modules, Components, and Systems VI

27 August 2013 | San Diego, California, United States

Showing 5 of 10 Conference Committees

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