Perovskite–silicon tandem solar cells are seen as a key technology for achieving efficiencies above 30 percent in photovoltaics. Their combination of a perovskite top cell layer and a highly efficient silicon bottom cell makes better use of sunlight than conventional single-junction cells.
So far, the highest efficiencies have been measured almost exclusively on small cell areas of about one square centimeter. These miniature test cells serve as a fast platform for evaluating materials and manufacturing processes in research. However, they do not always reflect the full efficiency potential — partly due to so-called perimeter losses.
As part of the NextGenPV project, our research team, together with Leibniz University Hannover, investigated how strongly the shaded part of the solar cell — the perimeter — influences the measurement results of perovskite–silicon tandem cells. Experimental measurements and simulations were carried out on two-terminal tandem cells with poly-silicon-passivated bottom cells. By selectively covering the cells with different masks and using numerical models, the team was able to assign voltage and efficiency losses to specific cell regions.
Key findings
- Best measured cell: 26.7% efficiency
- For an illuminated area of 1 cm², 1.2% absolute efficiency loss is attributed to the perimeter
- Simulations show that perimeter losses strongly depend on the ideality of individual solar cells and recombination at the cell edge
Why does this matter?
The results show that small cells often do not reflect their true efficiency potential. When comparing laboratory results across technologies, it is essential to consider not only the active cell area but also the edge regions.
The research team recommends that future efficiency reports include both the illuminated area and the perimeter area to ensure fair comparison of measurements across laboratories and technologies.
The findings help to better understand the transition from laboratory cells to industrial tandem solar cells. They support more targeted improvements in manufacturing processes and promote a consistent evaluation of new tandem technologies. This work makes an important contribution to advancing high-efficiency tandem solar cells.