Synthesis of CIS Quantum Dots in Low-Temperature Regime: Effects of Precursor Composition and Temperature Ramps

Copper Indium Sulfide (CIS) based quantum dots (QDs) have strong potential for future large-scale applications in photovoltaic, display, and optoelectronic sectors, partly due to their minimal toxicity. CIS QDs are usually grown at temperatures over 200 °C. In this work, we present a gram-scale, noninjection synthesis of CIS-based QDs in a low temperature regime and report, through systematic analyses, on the influence of temperature ramping profiles and precursor compositions on the properties of core CIS and core/shell CIS/ZnS QDs. It is established that the temperature ramp method is as important as the peak temperature itself. Nonabrupt temperature ramping results in core CIS QDs with more ligand coverage and fewer defects, and makes ZnS overgrowth possible even with lower Zn:S molar ratios. Precursor level molar ratios of 1:2 for Cu:In and 8:1 for Zn:S resulted in improved efficiency in CIS and CIS/ZnS QDs with strong and long-lived emissions in the 85-245 ns range. Implementing a dropwise addition of the ZnS precursor leads to prolonged QD extraction and shorter emission wavelengths. The different processes showed a wide range of tunability in the visible-to-IR range along with intense photoluminescence. The ZnS shell growth dependence on temperature ramping mode is explained through a mechanism for sulfur consumption, from the core or from the ligands' thiol groups. The low temperature regime processes, tunability for wide range of emissions, and identified pathways for long-lived emissions make these less-toxic, CIS-based QDs amenable to large area, scaled-up processing for device applications.