In
order to allow quantum dots with the desired physical and chemical
properties, the fine control and prediction of size during chemical
syntheses is a challenge that must be addressed. In this work, we
applied machine learning algorithms, with information extracted from
scientific papers, to identify the most important variables in the
synthesis of CdSe, CdS, PbS, PbSe, and ZnSe quantum dots. From the
random forest and gradient boosting machine algorithms, the most influential
parameters on the final diameter of the quantum dots were the time
of reaction, temperature, and metal precursors. Our models were applied
to suggest the best reaction parameters for a desired quantum dot
size. This methodology shall contribute to the quantum dot community
to save time and money while reaching the proper material conditions
for their applications.
Ternary sulfide nanostructures are small band gap materials that combine relatively low toxicity with useful optical properties for several applications, including photovoltaics. A systematic experimental study on the synthesis and mechanism of formation of copper thioantimonates (Cu 3 SbS 4 ) and thioantimonides (CuSbS 2 ) nanoparticles is presented. Antimony oxide (Sb 2 O 3 ) was formed in an initial step by hydrolysis with oleylamine. The injection of a sulfur precursor led to the conversion to Cu 3 SbS 4 driven by an excess of sulfur in oleylamine medium and at high temperatures (>200 °C). The sulfur excess was depleted as the reaction progressed, causing the reduction of the antimony(V) of the Cu 3 SbS 4 back to antimony(III). Consequently, the Cu 3 SbS 4 was converted to CuSbS 2 . In addition, the rate of antimony reduction increased with the reaction temperature. The formation mechanism unveiled here provides important insights toward the synthesis of analogous materials.
The optoelectronic properties of quantum dots are strongly controlled by the chemical nature of their surface-passivating ligands. In this work, we present the synthesis, characterization, and surface modification of CdSe quantum dots (QDs) and their application in solar cells. CdSe QDs were capped in oleic acid (OA), 3-mercaptopropionic acid (MPA), and 4-mercaptobenzoic acid (MBA). The QDs were characterized by transmission electron microscopy (TEM), UV-Vis absorption and emission spectrophotometry, thermogravimetric analyses, and 1H and 13C NMR. From TEM analysis, it has been observed that interparticle distance can be effectively controlled by the presence of different molecular size ligands. From the 1H and 13C NMR, specific types of interactions between the Cd2+ and the ligands have been observed. Although CdSe/OA presented larger interparticle distance as compared to CdSe/MPA and CdSe/MBA, the photocatalytic oxidation of the thiol groups on the surface of the MPA- and MBA-based quantum dots resulted in poor surface stabilization, ultimately resulting in poor power conversion efficiencies which were ca. 70% smaller than that of OA-based solar cell.
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