Energy-harvesting efficiency analysis for solar modules using 2T and 4T tandem solar cells

Robert Witteck, William E. McMahon, John F. Geisz, Qi Jiang, Emily L. Warren National Renewable Energy Laboratory, Golden, CO, United States

We present a framework to compare the energy-harvesting efficiency (EHE) of 2-terminal (2T) and 4-terminal (4T) tandem solar cells integrated into different module architectures. Our study considers perovskite solar cells (PSC) of varying band gaps combined to form all-perovskite tandems as well as PSC/silicon tandems. Examining top cells with varying band gaps shows that spectral variations only marginally impair the EHE of 2T devices if they employ band gaps that make them reasonably current matched. Although situational, we show how the EHE of 2T devices can perform as good or better than 4T devices when the unavoidable optical and series resistance losses for the module integration of 4T cells are included in the analysis. At the conference we will present a ray-tracing-assisted series-resistance model and detailed spectral EHE analysis to find the most suitable module architecture for 2T and 4T devices.