Quantum wells offer advantages in conventional bulk tandem solar cells since they allow the independent tailoring of the absorption edge of either cell with no lattice mismatch and subsequent relaxation. We describe progress in the band gap engineering of InGaP/GaAs solar cells using strain balanced quantum wells and present a tandem quantum well structure which has achieved 30.6% efficiency under 54 suns AM1.5g. This is a record for photovoltaic nanostructured devices. We predict realistic efficiencies of 34% under 600suns, AM1.5d low AOD for optimized devices. Finally, the possibility and potential gains of introducing quantum wells into both cells of an InGaP/GaAs device are discussed.
The effect of incorporating strain balanced multiquantum well structures in InGaP/GaAs monolithic tandem solar cells is investigated. At present the majority of InGaP/GaAs tandem cells are current limited by the bottom GaAs junction. Incorporation of multi-quantum well structures in the GaAs bottom junction extends the cell absorption to longer wavelengths. This allows current matched dual junction tandem cells to achieve higher efficiencies. InGaP/GaAs tandem cells have been studied by overgrowing different top cells on two similar quantum well structures and compared to a InGaP/GaAs control cell. A current matched top cell is presented and efficiency enhancement of a tandem by a quantum well cell demonstrated experimentally for the first time.
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