June 20, 2017 – Westford, MA
BrightSpot Automation has delivered its first ContactSpot-PRO system for performing non-destructive contact resistance measurements of solar cells. The system has been installed at the at the University of Central Florida (UCF) in the research group of Prof. Kris Davis.
The ContactSpot-PRO tool measures the contact resistivity between the metallization of a solar cell and the underlying semiconductor. This cell parameter is critical for optimization of the cell design, materials, and manufacturing process, yet it is rarely measured in practice due to the destructive nature of the standard linear TLM test. In the standard test, strips are cut from standard cells to isolate linear contact segments for testing, or special variable-spaced test structures are made, neither of which is desirable for manufacturing. The ContactSpot-PRO uses a circular TLM method where the resistance is measured between a center dot across a ring gap to the surrounding metallization over a range of ring gap dimensions. With such a geometry, no isolation cutting of the cell is necessary. The measurement can be performed in a few seconds to enable in-line measurements.
Dr. Andrew Gabor, CTO of BrightSpot: “The challenge for us in terms of industry acceptance was to implement the circular test structures without affecting cell performance or aesthetics. The solution we found was to make very small structures that we could hide within the standard busbars. After soldering of the interconnect wires in the panels, they will be covered up by the wires. We then implemented vision guided motion to measure the dimensions of each structure for the most accurate analysis and to allow alignment of the probehead to the structures. The ContactSpot-PRO represents yet another highly successful industry-academia collaboration between BrightSpot and UCF. We worked very closely with Professor Davis and UCF student Geoffrey Gregory to develop the technique and analysis and to optimize the tool performance. This is groundbreaking work, and we are excited to now provide the tool to R&D and production groups worldwide for improved experimentation and better factory quality control.”
Dr. Kris Davis, Assistant Professor of Materials Science and Engineering at the Univ. of Central Florida: “To our knowledge, our paper to be presented on June 26 at the IEEE Photovoltaics Specialists Conference will be the first reference of using the circular TLM approach for photovoltaics in the literature. Although this approach is used in other electronics industries, it has apparently been overlooked within the PV community. We are hopeful that other research groups and companies will send cells to us for testing so we can share what we have learned. We can supply the front silver screen artwork files and structure dimensions to facilitate such collaborations. We are excited to demonstrate the technique beyond standard cell architectures and apply it to plated metallization, heterojunction cells with TCO layers, back side PERC structures where Al has a very limited contact area with the silicon, and even to CdTe cells and other superstrate thin film cells and modules where shadow masks or other techniques could be used to pattern the back metal.”
Dr. Zhihao Yang, Professor of Materials Science and Energy Engineering, Foshan University, China and consultant to Gonda Electronic Technology, Co. Ltd.: “As a large solar cell metallization paste manufacturer, contact resistance is the most important parameter for Gonda to optimize. We perform many experiments daily on different paste compositions at different firing conditions for different cell types, and the ability for us to quickly and accurately measure contact resistivity on every cell we make would be invaluable. We were quite impressed with the results of the initial collaborative experiment with BrightSpot and UCF on cells that we provided over a range of conditions. The correlation between the standard TLM testing method and the new circular TLM method was very strong.”
The University of Central Florida (UCF) has several researchers, graduate students, and undergrads involved in various aspects of solar cell and solar panel R&D, with an emphasis on characterization equipment and testing methods. Additionally, UCF manages the Florida Solar Energy Center (FSEC). Further information about FSEC can be found at www.fsec.ucf.edu. Those interested in testing cells on the ContactSpot-PRO should contact Kris Davis at Kristopher.Davis@ucf.edu.
About BrightSpot Automation, LLC
BrightSpot Automation provides the PV industry and PV researchers with specialized manufacturing and measurement tools with a focus on improving module durability and performance. The company is based in Westford, MA.