Toward Low-Cost 4-Terminal GaAs//Si Tandem Solar Cells

Mechanically stacked III–V-on-Si (III–V//Si) tandem solar cells have demonstrated efficiencies beyond what can theoretically be achieved by single junction Si solar cells, but III–V costs are currently at least an order of magnitude higher than Si costs. Recent techno-economic analysis shows that costs could be substantially reduced by replacing traditional metalorganic vapor phase epitaxy (MOVPE) with a lower-cost III–V deposition technique, such as hydride vapor phase epitaxy (HVPE). This study analyzes the performance of an HVPE-grown GaAs top cell incorporated into a 4-terminal (4T) GaAs//Si tandem cell that achieved an efficiency of 29%, which is the highest solar cell efficiency fabricated without expensive deposition techniques such as MOVPE or MBE. We compare these results to an MOVPE-grown GaAs//Si tandem cell that has the same structure. Finally, we model optimizations to the HVPE-grown GaAs top cell and provide a near-term pathway to 31.4% efficiency with a low-cost III–V deposition technique.