29.9%-efficient, commercially viable perovskite/CuInSe₂ thin-film tandem solar cells

Despite the ease of fabrication and no current matching constraint in mechanically stacked thin-film-based tandem solar cells, both electrical and optical losses still limit the performance of wide-band-gap perovskite semi-transparent solar cells in such tandem devices. The thin-film tandems using both perovskite and CuInSe₂ (CIS) have not yet achieved optimal levels for commercial viability. Here, we present novel electrical and optical enhancement approaches to maximize the performance of perovskite front cells. We have introduced new electrical and optical techniques, using methyldiammonium diiodide and adjusting the optical interference spectrum. This resulted in a record efficiency of 20.2% (21.8% by J-V scan) for a semi-transparent perovskite cell and 81.5% average near-infrared transmittance. When paired with a CIS bottom cell, the tandem efficiency reached 29.9%. Techno-economic studies show that these tandems could deliver close to 2,000 Wh/m² daily for certain locations and offer competitive electricity costs, ranging from 3 to 5 USDcents/kWh within ±30° latitude.