Abstract Spectrum down-shifting converters based on Cd-free Zn–Cu–In–S(ZCIS)/ZnS core/shell quantum dots are modeled and simulated for applications in photovoltaics using the Monte-Carlo approach. The set of physical characteristics required for the successful implementation of this type of material in spectral converters have been identified. The advantage of using ZCIS/ZnS quantum dots in such converters is highlighted through a comparison with the conventional CdSe/ZnS quantum dots. The simulation model has been evaluated experimentally using ZCIS/ZnS quantum dots dispersed in polydimethylsiloxane (PDMS) as a spectrally converting top layer. In addition to validating the utility and precision of the simulation, it is shown that the polymerization of polydimethylsiloxane does not significantly impede the photoluminescent quantum yield of the ZCIS/ZnS quantum dots.