Technical papers & presentations:

Non-Destructive Contact Resistivity Measurements on Solar Cells Using the Circular Transmission Line Method; 44th IEEE Photovoltaic Specialist Conference, June 25 2017, Washington D.C.
We have developed a new tool to measure the contact resistance and sheet resistance of solar cells in a nondestructive and novel manner. With a simple change in the artwork for the metallization, small circular structures can be hidden within the busbars of the solar cells to enable the measurements with no impact on cell efficiency or aesthetics following the soldering of wires over the busbars.
Circular TLM - UCF and BrightSpot - IEEE[...]
Adobe Acrobat document [1.0 MB]
Evaluating Solar Cell Fracture as a Function of Module Mechanical Loading Conditions; 44th IEEE Photovoltaic Specialist Conference, June 28 2017, Washington D.C.
The LoadSpot mechanical load tester was used to study crack formation and crack opening as a function of load for different module and cell types.
LoadSpot testing for different modules -[...]
Adobe Acrobat document [1.0 MB]
Forecasting Environmental Degradation Power Loss in Solar Panels with a Predictive Crack Opening Test; 44th IEEE Photovoltaic Specialist Conference, June 28 2017, Washington D.C.
The LoadSpot mechanical load tester was used for static loading studies, followed by environmental chamber exposure, followed by cyclic loading tests. Measuring EL and IV under a low level of applied pressure was found to be a predictor of subsequent EL and IV degradation in some cases. Excessive new cracks were formed by light loading after chamber exposure.
LoadSpot testing post env chamber - UCF [...]
Adobe Acrobat document [639.0 KB]
Look while you load: Electroluminescence and IV testing of solar panels under mechanical load
Presentation from the 2017 NREL/SNL/BNL PV Module Reliability Workshop, Lakewood CO, February 28 2017
Load Testing - 2017 PVRW presentation - [...]
Adobe Acrobat document [7.1 MB]
TCAD MODELING OF TLM CONTACT RESISTANCE STRUCTURES; 32nd European Photovoltaic Solar Energy Conference and Exhibition, 21Jun2016, Munich, Germany
We have constructed TCAD and circuit simulator models for the measurement of contact resistivity on strips cut from solar cells. The models correctly predict trends in the measured contact resistivity as the sample width is varied. The models also show how the TLM is affected by the presence of unprobed contacts when measuring solar cells. The results are used to create correction factors that can be incorporated into the TLM measurement.
Contact Resistivity Modeling - UCF and B[...]
Adobe Acrobat document [1.4 MB]
Mechanical Load Testing of Solar Panels – Beyond Certification Testing; 43rd IEEE Photovoltaic Specialists Conference, 10Jun2016, Portland, OR
This paper presents an overview of mechanical load testing and cell cracking. We present the LoadSpot tool as a solution for improved load testing with the added benefit of a predictive crack opening test. We also present finite element modeling of different module structures and mounting methods.
Load Testing PVSC2016 paper - BrightSpot[...]
Adobe Acrobat document [1.1 MB]
Dependence of Solar Cell Contact Resistivity Measurements on Sample Preparation Methods; 43rd IEEE Photovoltaic Specialists Conference, 10Jun2016, Portland, OR
This paper describes TLM contact resistance measurements which explore the effects of test sample strip width and laser scribing parameters.
ContactSpot PVSC2016 paper - BrightSpot.[...]
Adobe Acrobat document [924.0 KB]
A Better Way to Bend: Vacuum and Air Pressure for Mechanical Load Testing of Solar Panels; NREL Photovoltaic Module Reliability Workshop 2016 (PVMRW)
This poster introduces our new product, the LoadSpot, which can perform static and dynamic load testing of solar panels as per IEC specifications. It has advantages over other methods of performing load testing in terms of pressure uniformity and the ability to characterize the panels by IV and EL testing while under load. Vacuum applied to the rear side temporarily opens up closed cracks and can serve as a predictive test of potential power loss were these cracks to open up in the field.
LoadSpot poster - PVMRW2016.pdf
Adobe Acrobat document [5.8 MB]
Cracked cell solutions; NREL Photovoltaic Module Reliability Workshop 2015 (PVMRW)
Provides background on the origins of microcrack and crack generation, and outlines several approaches that can be taken at the wafer, cell, module and system levels to both reduce the occurrence of cracked cells in the first place, and to reduce their impact when they do occur.
BrightSpot - Cracked cell solutions - NR[...]
Adobe Acrobat document [1.2 MB]
"Contact resistance measurement - observations on technique and test parameters" - IEEE PVSC conference June 2015
Background of contact resistance measurement techniques, and discusses the effects of test method and analysis algorithm on results
Contact resistance - BrightSpot - PVSC20[...]
Adobe Acrobat document [639.5 KB]
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