Multiscale Characterization to Study Contact and Interconnect Degradation in Photovoltaic Modules

The current popularity of photovoltaic (PV) systems is due to the fact that they are exceptionally reliable and significantly lower cost than other energy sources. Studying cell and module degradation is key to promote further development in the state of the art. Fielded or accelerated aged modules exhibit different failure modes, of which metallization degradation (contacts and interconnections) is prevalent. In this work, we discuss how multiscale characterization methods can be applied to a variety of module technologies that have been field exposed and have undergone accelerated age testing. These methods include performing characterization on module level, cell level, and finally on the materials level. The observed performance losses from the module and cell level characterization can be co-related to materials properties to find out the root cause of degradation. The initial characterization suite included module and cell-level current-voltage (I-V), Suns-VOC, photoluminescence (PL) and electroluminescence (EL) imaging, quantum efficiency, UV fluorescence imaging, etc. Samples are then extracted from particularly degraded regions of the module and prepared for materials characterization techniques like top-down and crosssectional scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), Secondary ion mass spectroscopy (SIMS), Raman microspectroscopy, Transmission electron microscopy (TEM), etc. allowing a deeper look into the mechanism behind the metallization degradation. This article serves as a one-stop guide to introduce the different multiscale characterization methods and how they can be effectively applied to perform PV degradation studies. Here we show our findings and how they are co-related to determine This material is based upon work supported by the U.S. Department of Energy’s Office of Energy Efficiency and Renewable Energy (EERE) under the Solar Energy Technologies Office Agreement Number DE-EE0008172, DE-EE0008155, and DE-EE0009347. (Corresponding author: Nafis Iqbal and Kristopher O. Davis) N Iqbal, DJ Colvin, JP Ganesan, P Banerjee and KO Davis are with the Department of Materials Science and Engineering, University of Central Florida, Orlando, Florida, USA (e-mail: nafisiqbal@knights.ucf.edu; dylanjc43@knights.ucf.edu; jeyaprakashganesan@knights.ucf.edu; parag.banerjee@ucf.edu; kristopher.davis@ucf.edu). N Iqbal, DJ Colvin and KO Davis are with the Resilient Intelligent Sustainable Energy Systems Faculty Cluster, University of Central Florida, Orlando, Florida, USA. DJ Colvin and KO Davis are with the FSEC Energy Research Center, Cocoa, Florida, USA. AJ Curran and RH French are with the Materials Science and Engineering, Case Western Reserve University, Cleveland, Ohio, USA (email: ajc269@case.edu; rxf131@case.edu). F Li and G TamizhMani are with the Photovoltaic Reliability Laboratory, Arizona State University, Mesa, Arizona, USA (email: fangli3@asu.edu; manit@asu.edu). J Karas is with the National Renewable Energy Laboratory (NREL), Golden, Colorado, USA (email: joseph.karas@nrel.gov). JN Jaubert is with Canadian Solar, Inc., Guelph, Ontario, Canada (email: jn.jaubert@csisolar.com). BD Huey is with the Institute of Materials Science, University of Connecticut, Storrs, Connecticut, USA (email: bryan.huey@uconn.edu). KO Davis is with CREOL, the College of Optics and Photonics, University of Central Florida, Orlando, Florida, USA. the specific failure mechanisms for each of the characterization methods.