TCO optimization for solar modules with 4T perovskite/silicon tandem cells for standard testing conditions and outdoor operation

Robert Witteck, Paul Ndione, San Theingi, William McMahon, Christian Velez, William Nemeth, Joseph Luther, Lance Wheeler, John Geisz, Axel Palmstrom, Emily Warren National Renewable Energy Laboratory, Golden, CO, United States

We combine optical and series resistance modeling to optimize the efficiency of solar modules with 4-terminal (4T) perovskite/silicon tandem devices for standard testing conditions (STC) and outdoor operation. Our analysis focuses on the front and rear side transparent conductive oxide (TCO) layers of the wide bandgap top cell. We find that selecting the best TCO layer solely on transmittance and sheet resistance is insufficient for an optimal 4T performance. Instead, comprehensive optical and resistive modeling is crucial to identify the most effective TCO configuration for an improved module efficiency. We apply our model to evaluate the energy harvesting potential of 4T perovskite/silicon tandem solar modules for various U.S. locations. Our results reveal that the TCO layers optimal for outdoor operation differ from those ideal under STC, highlighting the necessity to adapt the TCO layers when moving from record cell efficiency designs to real-world operation.