Current-matched triple-junction solar cell reaching 41.1% conversion efficiency under concentrated sunlight

A metamorphic ${\text{Ga}}_{0.35}{\text{In}}_{0.65}\text{P}/{\text{Ga}}_{0.83}{\text{In}}_{0.17}\text{As}/\text{Ge}$ triple-junction solar cell is shown to provide current-matching of all three subcells and thus composes a device structure with virtually ideal band gap combination. We demonstrate that the key for the realization of this device is the improvement of material quality of the lattice-mismatched layers as well as the development of a highly relaxed ${\text{Ga}}_{1-y}{\text{In}}_y\text{As}$ buffer structure between the Ge substrate and the middle cell. This allows the metamorphic growth with low dislocation densities below ${10}^6{\text{cm}}^{-2}$ . The performance of the approach has been demonstrated by a conversion efficiency of 41.1% at 454 suns ($454\text{kW}/{\text{m}}^2$ , AM1.5d ASTM G173–03).