Radiative and Nonradiative Recombination in CuInS₂ Nanocrystals\nand CuInS₂‑Based Core/Shell Nanocrystals

Abstract

Luminescent\ncopper indium sulfide (CIS) nanocrystals are a potential solution\nto the toxicity issues associated with Cd- and Pb-based nanocrystals.\nHowever, the development of high-quality CIS nanocrystals has been\ncomplicated by insufficient knowledge of the electronic structure\nand of the factors that lead to luminescence quenching. Here we investigate\nthe exciton decay pathways in CIS nanocrystals using time-resolved\nphotoluminescence and transient absorption spectroscopy. Core-only\nCIS nanocrystals with low quantum yield are compared to core/shell\nnanocrystals (CIS/ZnS and CIS/CdS) with higher quantum yield. Our\nmeasurements support the model of photoluminescence by radiative recombination\nof a conduction band electron with a localized hole. Moreover, we\nfind that photoluminescence quenching in low-quantum-yield nanocrystals\ninvolves initially uncoupled decay pathways for the electron and hole.\nThe electron decay pathway determines whether the exciton recombines\nradiatively or nonradiatively. The development of high-quality CIS\nnanocrystals should therefore focus on the elimination of electron\ntraps.