I'm investigating the performance limits of thin film silicon multi-junction solar cells under laboratory (ideal) conditions. Specifically, I'm interested in understanding what the upper bound for the initial conversion efficiency is before any degradation effects come into play. From the literature, tandem devices that combine amorphous and microcrystalline silicon layers have been reported to reach relatively high initial efficiencies compared to single-junction cells. However, I’d like to know the consensus or typical value cited in recent research. Any insights or references to experimental results or theoretical models would be greatly appreciated.