Optimization of the recipe for the synthesis of CuInS₂/ZnS nanocrystals supported by mechanistic considerations

Abstract

CuInS 2 /ZnS (CIS/ZnS) quantum dots (QDs) with high photoluminescence (PL) were synthesized via a facile solvothermal approach. Gaussian deconvolution of PL spectra, transmission electron microscopy, and timeresolved PL spectroscopies were used to characterize the emission properties of the prepared CIS and CIS/ZnS QDs. It was found that the growth of ZnS can reduce the surface defect acting as traps to minimize donor-acceptor emissions, and the contribution of band to donor/acceptor transition becomes a dominating emission with the increase of shell growth time. The blue shift of PL emission wavelength of CIS/ZnS QDs underwent two steps: the dramatic blue shift originated from the decreased fraction donor-acceptor transition due to the reduction of surface defects at the beginning and the subsequently mild blueshift with the time from the interdiffusion of CIS and ZnS. The effect of trioctylphosphine (TOP) and dodecanethiol (DDT) as ligands during shell growth on the optical properties of QDs were investigated and compared. The PL quantum yield (QY) of CIS core affects the final value of CIS/ ZnS QDs, and the higher PL QY is achieved while using CIS core with higher PL QY. Based on the selected ligand DDT, the reaction parameters, such as CIS core reaction time, shell growth time, and Zn/Cu feed molar ratio, were further optimized. CIS/ZnS QDs with high PL QY can be obtained with a Zn/Cu feed molar ratio larger than 4, shell growth time of 30 to 90 min, and shell growth temperature 220°C-240°C, and the maximum value was up to about 80% by adjusting the above-mentioned parameters.

Neural network modeling and simulation of the synthesis of CuInS2/ZnS quantum dots

“…It is obvious that the ligand type has critical impact on the optical performance but the effect of other variables, for example, the time of the shell growth is quite similar. The simulation results are conformed with our previous research . TOP can coordinate with ZDC to form complex and as weak Lewis base efficiently interact with weak Lewis acid (Cu + ) at low temperature, this effect greatly increases the precursor activity, resulting in faster growth rates of the ZnS shell.…”

“…The reasons for the QY growth below the maximum have been already discussed. The decrease of the yield above the maximum is caused by the surface defects that are generated due to the decomposition of DDT . The same behavior has been predicted in the whole temperature range (220°C‐240°C).…”

“…During the growth of ZnS shell, the ion exchange of core and shell induced the shrink of CIS core, which lead to the continuous blueshift and even became dominated at latter time. The detailed mechanistic interpretation is given elsewhere . Higher shell growth temperature can accelerate the shrink of CIS core and induce larger blueshift.…”

“…The observed redshift of emission peak can be explained by the reduced confinement effect related to the growth of particles and the evolution of QYs is related to the numbers of surface defects. For the detailed discussion, we refer to our previous article …”

“…All the experimental conditions and obtained results are presented in the SI part (see Table S1). Detailed information on experimental, equipment, procedures, and analytics is given in the SI as well as in References and . From the full database, 80% of the experimental data were used for the training set and the other 20% of the experimental data were used as validation set, respectively (5‐fold crossvalidation).…”