Energy Yield and Performance Ratio of III-V on Silicon Dual Junction Solar Cells in Different Climate Zones

The importance of predicting outdoor performance of tandem solar devices is growing, as silicon-based tandem solar cells approach industrialization. A 2-terminal configuration has the advantage of lower parasitic absorption and less electrical wiring at module level as compared to a 4-terminal device. However, a 2-terminal tandem device is sensitive to current-mismatch losses. As a result, there is a strong interest to determine the outdoor energy yield in addition to the STC efficiency in order to evaluate the real impact of current-mismatch losses on the energy yield. We compare the energy yield, harvesting efficiency and performance ratio of a silicon-based dual junction solar cell in 2- and 4-terminal configuration to a silicon single junction device for different locations in the world. We find that changes due to current mismatch do not lead to a relevant decrease in harvesting efficiency in 2-terminal tandem solar cells and thus are no reason to principally prefer 4-terminal tandem solar cells. The assumption that current mismatch might be a severe issue in 2-terminal tandems does not hold - they show similar performance as silicon single-junction devices. Note that the performance ratio of 4-terminal tandems shows a lower dependence on location than 2-terminal tandems as well as single junction solar cells, and thus for certain locations show an exceptionally high performance ratio.