CuInS2 Quantum Dots with Thick ZnSexS1-x Shells for a Luminescent Solar Concentrator

The photoluminescence quantum yield (PLQY) of copper indium sulfide (CIS) quantum dots (QDs) improves significantly after a shelling procedure as the shell materials, like zinc sulfide, mitigate surface defects and reduce nonradiative recombinations. However, it is widely observed that the PLQY reduces when QDs are cast as a solid film from their solution, and PL peak emission also red-shifts, which suggests a relaxation of the quantum confinement effect. This could be due to thin zinc sulfide shells. Unlike cadmium-based QDs, reports on a thick zinc chalcogenide shell on CIS QDs are limited. Efforts to grow larger shells have been stymied by zinc diffusion toward the core, causing cation exchange and alloy formation. Thick zinc chalcogenide shell growth typically requires higher temperatures, a regime which would irreversibly degrade the PL of a CIS QD. Here, we develop a technique to grow thicker shells on CIS QDs to improve the quantum confinement effect between the QDs. With these thick shell CIS QDs, we demonstrate better emission as well as thermal and chemical stability. Finally, we demonstrate their application in a luminescent solar concentrator and showed that it has better light harvesting characteristics than its thin shell counterpart.