Abstract
Highly photoluminescent core/shell CuInS2/ZnS (CIS/ZnS) nanocrystals were synthesized. Zinc acetate and dodecanethiol in octadecene solvent were used for shell growth. The structure and composition of QDs were investigated with inductively coupled plasma‐optical emission spectroscopy, X‐ray photoelectron spectroscopy, and transmission electron microscopy. The crystal phase of CIS was tetragonal chalcopyrite. Based on X‐ray diffraction analysis, it has been concluded that the growth of the ZnS shell did not affect the phase structure of CuInS2 (CIS). Photoluminescence (PL) quantum yield (QY) of CIS increased to 80% after epitaxial growth of ZnS, and the PL emission wavelength can be feasibly tuned to be in the range of 560–710 nm by adjusting shell growth time. The superb photostability with high PL QY of CIS/ZnS nanocrystals is ascribed to the gradient of the chemical composition that has been formed between the core and the shell.
Highlights
Semiconducting nanocrystals or quantum dots (QDs) are characterized by a quantum confinement of electron and hole in all three dimensions, which leads to an increase in the effective band gap of the material and shifts of both the optical absorption and emission of semiconducting QDs depending on the particle size; larger particles display smaller band gaps while smaller particles show larger band gaps
CIS core QDs were prepared based on the recipe published in the literature [25]; ZnS precursor containing zinc acetate, dodecanethiol (DDT), and octadecene (ODE) was injected into the same reactor with existing CIS cores that have not been purified for ZnS shell growth
DDT was used as the S source as well as a capping ligand. This is a green, simple, and economical method to obtain highly luminescent and structurally stable QDs for the following reasons: only affordable and nontoxic materials were used in the synthesis; the solvent, S source, and ligand used in the shell growth step were the same as those in the CIS core synthesis, which simplified the separation steps in postprocess treatment and saves cost in large scale production
Summary
Semiconducting nanocrystals or quantum dots (QDs) are characterized by a quantum confinement of electron and hole in all three dimensions, which leads to an increase in the effective band gap of the material and shifts of both the optical absorption and emission of semiconducting QDs depending on the particle size; larger particles display smaller band gaps while smaller particles show larger band gaps. Ternary semiconductors based on IB, IIIA, and VIA elements of the periodic classification (I-III-VI2 type semiconductors) including CuInS2 (CIS), CuInSe2 (CISe), AgInS2 (AIS), and CuGaS2 (CGS) have shown promising results for applications in these fields Among these semiconductors, CIS semiconductors have been receiving considerable attention because of their low toxicity, high energy conversion efficiency, high light absorption coefficient (α ≈ 105 cm−1) [20], and low production cost, which are desired properties for photovoltaic applications. A simple synthetic process for the growth of ZnS on CIS surface was developed in order to improve PL efficiency of CIS QDs. During the synthesis, CIS core QDs were prepared based on the recipe published in the literature [25]; ZnS precursor containing zinc acetate, dodecanethiol (DDT), and octadecene (ODE) was injected into the same reactor with existing CIS cores that have not been purified for ZnS shell growth. This is a green, simple, and economical method to obtain highly luminescent and structurally stable QDs for the following reasons: only affordable and nontoxic materials were used in the synthesis; the solvent, S source, and ligand used in the shell growth step were the same as those in the CIS core synthesis, which simplified the separation steps in postprocess treatment and saves cost in large scale production
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