Throughput optimized a-Si/μc-Si tandem solar cells on sputter-etched ZnO substrates

► The impact of layer thickness on a-Si/μc-Si tandem cell efficiency was carefully investigated. ► Stable module efficiencies above 10% can be achieved with 0.9 μm bottom cell thickness. ► Thin tandem cells made with low top cell deposition rate give the highest productivity. ► Sputter-etched ZnO is an excellent substrate for high efficiency tandem cells.