Article Link Computational and experimental data and analyses for the Nature Photonics article: Kavanagh, S.R. & Wang, Y. et al. Cation disorder engineering yields AgBiS2 nanocrystals with enhanced optical absorption for efficient ultrathin solar cells. Nat. Photon. (2022). https://doi.org/10.1038/s41566-021-00950-4 Abstract: Strong optical absorption by a semiconductor is a highly desirable property for many optoelectronic and photovoltaic applications. The optimal thickness of a semiconductor absorber is primarily determined by its absorption coefficient. To date, this parameter has been considered as a fundamental material property, and efforts to realize thinner photovoltaics have relied on light-trapping structures that add complexity and cost. Here we demonstrate that engineering cation disorder in a ternary chalcogenide semiconductor leads to considerable absorption increase due to enhancement of the optical transition matrix elements. We show that cation-disorder-engineered AgBiS2 colloidal nanocrystals offer an absorption coefficient that is higher than other photovoltaic materials, enabling highly efficient extremely thin absorber photovoltaic devices. We report solution-processed, environmentally friendly, 30-nm-thick solar cells with short-circuit current density of 27 mA cm−2, a power conversion efficiency of 9.17% (8.85% certified) and high stability under ambient conditions.