Structural and Electronic Reconstruction of Extended Defects in Pnictogen Chalcohalides.

With growing global demand for renewable energy, thin-film photovoltaic technologies are emerging as a promising route to low-cost, scalable solar power. However, for many candidate materials extended defects in polycrystalline thin films are associated with deep gap states that limit carrier lifetimes and reduce device efficiency. Pnictogen chalcohalide semiconductors with the general formula MChX (M = pnictogen, Ch = chalcogen, X = halogen) have been proposed as defect-tolerant alternatives. Using density functional theory, we predict the structure and electronic properties of surface defects for eight pnictogen chalcohalide compounds and analyze their behavior upon surface reconstruction. Our results reveal that, despite the cleavage of covalent bonds, these materials undergo reconstructions that eliminate detrimental gap states. The facile formation of new interchain bonds at the surface preserves the electronic performance of the materials and suggests intrinsic resilience to extended defects. These findings position pnictogen chalcohalides as promising candidates for defect-tolerant, stable, thin-film photovoltaic absorbers.