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Buonassisi (MIT) 2011
Solar Cell Characterization
Lecture 16 – 11/8/2011 MIT Fundamentals of Photovoltaics
2.626/2.627 Tonio Buonassisi
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Buonassisi (MIT) 2011
1. Describe basic classifications of solar cell characterization methods.
2. Describe function and deliverables of PV characterization techniques measuring Jsc losses.
3. Describe function and deliverables of PV characterization techniques measuring FF and Voc losses.
Learning Objectives: Solar Cell Characterization
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Buonassisi (MIT) 2011
Liebig’s Law of the Minimum
total absorptionexcitation drift/diffusion separation collection
S. Glunz, Advances in Optoelectronics 97370 (2007)
Image by S. W. Glunz. License: CC-BY. Source: "High-Efficiency CrystallineSilicon Solar Cells.” Advances in OptoElectronics (2007).
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Buonassisi (MIT) 2011
Taxonomy of PV Device Characterization Techniques
1. By property tested: Electrical, structural, optical, mechanical...
2. By device performance metric affected: Manufacturing yield, reliability, efficiency (short-circuit current, open-circuit voltage, fill factor)…
3. By location (throughput): In-line (high throughput) vs. off-line (low throughput).
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Buonassisi (MIT) 2011
1. Describe basic classifications of solar cell characterization methods.
2. Describe function and deliverables of PV characterization techniques measuring Jsc losses.
3. Describe function and deliverables of PV characterization techniques measuring FF and Voc losses.
Learning Objectives: Solar Cell Characterization
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Buonassisi (MIT) 2011
Short Circuit Current
• Optical Reflection
• Spectral Response
• Minority Carrier Diffusion Length
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Buonassisi (MIT) 2011
Optical Reflection
Spectrophotometer: Measures specular and diffuse reflectance, and transmission.
Please see the lecture 16 video to see a photo of a spectrophotometer.
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Buonassisi (MIT) 2011
Increasing Absorption
Courtesy of Christiana Honsberg. Used with permission.
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Buonassisi (MIT) 2011
Increasing Absorption
Effect of Textured Surfaces on Light Absorption
SEM image of textured silicon
Q: What other mechanisms exist to trap light?
Courtesy of Christiana Honsberg. Used with permission.
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Buonassisi (MIT) 2011
Collection Probability
Courtesy of Christiana Honsberg. Used with permission.
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Buonassisi (MIT) 2011
Collection Probability
Courtesy of Christiana Honsberg. Used with permission.
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Buonassisi (MIT) 2011
Collection Probability
p-type
n-type
Courtesy of Christiana Honsberg. Used with permission.
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Buonassisi (MIT) 2011
Collection Probability
Courtesy of Christiana Honsberg. Used with permission.
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Buonassisi (MIT) 2011 Newport Spectral Response tool
Spectral Response
© Newport Corporation. All rights reserved. This content is excluded from our CreativeCommons license. For more information, see http://ocw.mit.edu/fairuse.
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Buonassisi (MIT) 2011
Spectral Response
Standards: IEC 60904-3 and 60904-8
from PVCDROM
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Buonassisi (MIT) 2011
External vs. Internal Quantum Efficiency
IQE = EQE
1R =
Electrons Out
Photons In 1R … where R = Reflectivity
Internal Quantum Efficiency
© source unknown. All rights reserved. This content is excluded from our CreativeCommons license. For more information, see http://ocw.mit.edu/fairuse.
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Buonassisi (MIT) 2011
Spectrally-Resolved Laser Beam Induced Current (SR-LBIC)
• 4 or more lasers measure IQE(l).
• Digital processing of data extracts relevant device parameters.
• XY stage moves sample.
• A 2D map of IQE obtained!
• In advanced versions, all lasers fire simultaneously (as they are pulsed at different frequencies) into a fibre optic cable. FFT of the current signal decouples different wavelengths.
Please see the lecture 16 video or the link below for a visual of the instrument.
http://www.isfh.de/institut_solarforschung/media/sr_lbic_messplatz_1.jpg
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Buonassisi (MIT) 2011
Minority Carrier Diffusion Length
See: P. A. Basore, IEEE Trans. Electron. Dev. 37, 337 (1990).
At each point… Mapped over an entire sample…
Graph and photo © source unknown. All rights reserved. This content is excluded from ourCreative Commons license. For more information, see http://ocw.mit.edu/fairuse.
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Buonassisi (MIT) 2011
1. Describe basic classifications of solar cell characterization methods.
2. Describe function and deliverables of PV characterization techniques measuring Jsc losses.
3. Describe function and deliverables of PV characterization techniques measuring FF and Voc losses.
Learning Objectives: Solar Cell Characterization
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Buonassisi (MIT) 2011
Voc and Operating Conditions
• IV Curve Measurements
• Series Resistance
– Contact Resistance
– Sheet Resistance
• Shunt Resistance
– Lock-in Thermography
• Electroluminescence
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Buonassisi (MIT) 2011
Refresher: Open Circuit Voltage
Courtesy of Christiana Honsberg. Used with permission.
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Buonassisi (MIT) 2011
J JL J01expq(V JRs)
kT
J02 exp
q(V JRs)
2kT
V JRs
Rshunt
Two Diode Model
diffusion current recombination current
Equivalent Circuit Diagram of Solar Cell
Rp = Rshunt. For good solar cell,
this must be large.
Rs = Rseries. For good solar cell,
this must be small.
Rs = Rseries. For good solar cell,
this must be small.
Rs = Rseries. For good solar cell,
this must be small.
J01 J02Rp
Rs
β1 β2Vja
V
Image by MIT OpenCourseWare.
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Buonassisi (MIT) 2011
IV Curve Measurements
Rs
J01
J02
Rsh
J JL J01expq(V JRs)
kT
J02 exp
q(V JRs)
2kT
V JRs
Rshunt
Note: You may see this formula with
sign of current inverted. Simply multiply each “J”
by “-1”.
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Buonassisi (MIT) 2011
#9 #14 #100
FZ, e.s.r. 85-101/sq.
#14 #100 #124
FZ, e.s.r. 79-87/sq.
IV Curve Measurements
Several IV curves for real solar cells, illustrating a variety of IV responses!
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Buonassisi (MIT) 2011
Physical Causes of Series Resistance
Courtesy of Christiana Honsberg. Used with permission.
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Buonassisi (MIT) 2011
Physical Causes of Shunt Resistance
Paths for electrons to flow from the emitter into the base. Can be caused by physical defects (scratches), improper emitter formation, metallization over-firing, or material defects (esp. those that traverse the space-charge region).
Potential barrier for electrons at a forward-biased n+p junction crossed by a charged extended defect. O. Breitenstein et al., “EBIC investigation of a 3-Dimensional Network of Inversion Channels in Solar Cells on Silicon Ribbons,” Solid State Phenomena 78-79, 29-38 (2001).
Courtesy of Trans Tech Publications and Otwin Breitenstein. Used with permission.
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Buonassisi (MIT) 2011
J JL J01expq(V JRs)
kT
J02 exp
q(V JRs)
2kT
V JRs
Rshunt
Effect of Rs and Rsh
Courtesy of Christiana Honsberg. Used with permission.
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Buonassisi (MIT) 2011
Lock-in Thermography
Lock-in Thermography Images Shunts (e.g., Local Increases in Dark Forward Current)
See the lecture 16 video for related visuals and explanation.
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Buonassisi (MIT) 2011
Lock-in Thermography
M. Kaes et al., Prog. Photovolt. 12, 355 (2004) J. Isenberg and W. Warta, Prog. Photovolt. 12, 339 (2004) O Breitenstein et al., Solar Energy Mater. Solar Cells 65, 55 (2001)
© Wiley. All rights reserved. This content is excluded from our CreativeCommons license. For more information, see http://ocw.mit.edu/fairuse.
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Buonassisi (MIT) 2011
Lock-in Thermography - Sensitivity
Sensitivity is a function of integration time.
rattlesnake!
O Breitenstein et al., Solar Energy Mater. Solar Cells 65, 55 (2001)
Courtesy of Elsevier, Inc., http://www.sciencedirect.com. Used with permission.
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Buonassisi (MIT) 2011
Lock-in Thermography – Dark vs. Illuminated
Dark Illuminated
M. Kaes et al., Prog. Photovolt. 12, 355 (2004) O Breitenstein et al., Solar Energy Mater. Solar Cells 65, 55 (2001)
© Wiley. All rights reserved. This content is excluded from our CreativeCommons license. For more information, see http://ocw.mit.edu/fairuse.
Courtesy of Elsevier, Inc., http://www.sciencedirect.com. Used with permission.
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Buonassisi (MIT) 2011
J JL J01expq(V JRs)
kT
J02 exp
q(V JRs)
2kT
V JRs
Rshunt
Lock-in Thermography – Imaging Losses
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Buonassisi (MIT) 2011
525mV Forward Biased (Voc = 571mV) 8Hz, 2hour scan, (30000 Frames)
White-light LBIC (essentially probes the bulk, below the emitter)
Correlation between Thermography and LBIC
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Buonassisi (MIT) 2011
See: “Shunt imaging in solar cells using low cost commercial liquid crystal sheets” C. Ballif et al., Proc. IEEE Photovoltaic Specialists Conference, 2002, pp. 446- 449.
Liquid Crystal Thermochromic Sheets
Cheaper Methods of Shunt Detection:
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Buonassisi (MIT) 2011
Electroluminescence
Images courtesy ISFH
Module Cell
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Buonassisi (MIT) 2011
Evolution of IR Imaging Techniques
Kasemann, M., et al. “Progress in Silicon Solar Cell Characterization with Infrared Imaging Methods.” Proceedings of the 23rd European Photovoltaic Solar Energy Conference (2008): 965-973.
© Martin Kasemann. All rights reserved. This content is excluded from our CreativeCommons license. For more information, see http://ocw.mit.edu/help/faq-fair-use/.
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Buonassisi (MIT) 2011
Suns-Voc
•Measures Voc as a function of illuminationcondition, with decaying flash lamp.
•Useful for decoupling series resistance losses from other defects.
•Commercialized by Sinton Instruments.
Sinton and Cuevas, Proc. 16th EU-PVSEC (Glasgow, UK, 2000).
© R. A. Sinton and A. Cuevas. All rights reserved. This content is excluded from ourCreative Commons license. For more information, see http://ocw.mit.edu/fairuse.
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2.627 / 2.626 Fundamentals of PhotovoltaicsFall 2013
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