Tailoring nanoscale interfaces for perovskite-perovskite-silicon triple-junction solar cells

Triple-junction solar cells theoretically outperform their double-junction and single-junction counterparts in power conversion efficiency, yet practical perovskite-perovskite-silicon devices have fallen short of both theoretical limits and commercial targets. To address surface defects in the top perovskite junction, we introduce a piperazine-1,4-diium chloride treatment, which replaces less stable lithium fluoride. For interfacing the top and middle perovskite junctions, we optimize the size of gold nanoparticles deposited on atomic layer-deposited tin oxide for best ohmic contacting with minimal optical losses. Applying these strategies, our champion 1-cm² triple-junction cell achieved a third party-verified reverse-scan power conversion efficiency of 27.06% with an open circuit voltage of 3.16 V. Scaling up to 16 cm², the device produced a certified steady-state power conversion efficiency of 23.3%. Device longevity also improved by eliminating methylammonium and incorporating rubidium into the perovskite bulk alongside the piperazine-1,4-diium chloride surface layer. An encapsulated 1-cm² cell retained 95% of its initial efficiency after 407 h at maximum power point and passed the IEC 61215 thermal cycling test. These results represent advancements towards efficient and stable perovskite-perovskite-silicon triple-junction solar cells.