The performance of quad-junction Ge based III-V multi-junction solar cells depends upon successful integration of a 1.0eV sub-cell into the existing InGaP/In0.01GaAs/Ge stack. The SiGeSn ternary alloy offers a means to fabricate a lattice-matched, 1.0eV sub-cell with the advantage that SiGeSn has both a tuneable band-gap and variable lattice parameter, enabling the material to be integrated into lattice-matched multi-junction architectures. A 1eV SiGeSn junction has been grown as both a single junction device and as the third junction in a InGaP/In0.01GaAs/SiGeSn triple junction device.
The SiGeSn junction produces sufficient current to almost current match the InGaP and In0.01GaAs junctions and achieves a peak external quantum efficiency > 80% is demonstrated suggesting a lower limit on the base minority hole diffusion length of 5m. However, a degradation in open-circuit voltage and fill factor are observed with the SiGeSn sub-cell. This low voltage from the SiGeSn subcell is is attributed to recombination from defect levels within the SiGeSn band gap.
Roucka, R., Clark, A., Wilson, T., Thomas, T., Fuhrer, M., Ekins-Daukes, N.J., Johnson, A., Hoffman, R. and Begarney, D., 2016, June. 3J solar cells comprising a lattice matched epitaxial SiGeSn subcell. In Photovoltaic Specialists Conference (PVSC), 2016 IEEE 43rd (pp. 2362-2365). IEEE.
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Category: Solar & Photovoltaics