Laser-based measurement of tunnel junctions in triple-junction solar cells: Lab-scale characterization and in-line screening

A laser-based system capable of characterizing tunnel junction behaviour in multi-junction cells has been developed. Incident flux density and therefore local current density is varied, while keeping total current constant. Current-voltage (IV) curves show characteristic dips due to exceeding the current density threshold beyond which the tunnel junction behaves non-linearly (J_peak). This approach has been validated through correlation with on-sun results. The ability to distinguish which tunnel junction is problematic within a multi-junction solar cell stack is also demonstrated. The design of a relatively simple and low-cost bench-top test system is presented, as well as a version suitable for inline screening. This work affords the development and selection of cells appropriate for implementation in high-efficiency, low-cost CPV designs.