Ab-initio assessment of new sulfo-iodide compounds as candidate top-cell materials for silicon-based multi-junction tandem solar cells

New semiconductors having the potential for excellent performance, scalable manufacturing and stability on a 25 year horizon are needed to enable silicon tandem solar cells. Here we explore theoretically a new class of non-toxic sulfoiodide compounds (CuxZnySyIx) has the potential to crystallize with the 4-fold coordinated “adamantine” structure. The band gaps predicted may be suitable for silicon multi-junction tandems. Initial calculations show tolerance to Cu vacancies, which do not appear to lead to deep levels in the band gap. These materials could potentially offer the “best of both worlds,” solution processability like an iodide and improved stability like a sulfide.