New eutectic method boosts efficiency of large-area perovskite-silicon solar tandems

Researchers created a formamidinium eutectic that lowers evaporation temperature, enabling stable thermal deposition of perovskite layers and achieving 31.5% efficiency on small cells and 30.0% on 200 cm² modules.

A team of scientists developed a formamidinium-based eutectic that depresses the evaporation temperature of formamidinium iodide by roughly 36 °C, preventing thermal breakdown during high-temperature deposition. This innovation produced perovskite films with superior crystal quality and atomic-scale uniformity when applied by thermal evaporation. Sequentially evaporated perovskite/silicon tandem devices demonstrated a steady-state conversion efficiency of 31.5% on laboratory-scale 1 cm² cells.

Extending the process to a commercial half-cut G12 silicon wafer yielded a 200 cm² tandem module with 30.0% efficiency, marking the smallest efficiency loss (3.99% relative) reported for area scaling in perovskite tandems. The eutectic-based modules maintained 95% of their initial output after 2000 hours of damp-heat aging at 85 °C/85% RH and exhibited virtually no power degradation over two months of real-world outdoor testing. These results suggest a viable path toward industrially scalable, reliable perovskite-silicon solar technologies.