An Integrated, Multipart Experiment: Synthesis, Characterization, and Application of CdS and CdSe Quantum Dots as Sensitizers in Solar Cells

Abstract

Quantum dots (QDs) are useful for demonstrating the particle-in-a-box (PIB) model utilized in quantum chemistry, and can readily be applied to a discussion of both thermodynamics and kinetics in an undergraduate laboratory setting. Modifications of existing synthetic procedures were used to create QDs of different sizes and compositions (CdS passivated with polymer, and CdSe passivated with oleic acid/ trioctylphosphine). These were investigated by spectroscopy, to which standard 3D PIB mathematical models were applied to determine their effective size. The data were compared to those from other methods for students to see the validity of the PIB model. For CdSe QDs, an empirical formula was applied to the spectroscopic data. In the case of CdS, the synthesized QDs were studied with X-ray diffraction, from which one can also estimate the size of the QDs. Finally, the QDs were utilized as the light-harvesting layer in photovoltaic cells by attachment to a layer of surface-modified titania (TiO 2 ) nanoparticles on conductive glass, and the surface chemistry tested via water contact-angle measurements. The photoresponse of these cells was measured using basic electrochemistry equipment for a selection of QDs, and these results were considered in relation to the light source used for excitation (CdS QDs absorb UV light, and a voltage was only measurable upon exposure to UV light). Students are able to synthesize, characterize, and apply their materials to a functional purpose. Ultimately, students drafted reports in the form of an ACS-style communication, allowing for a tie-in of typical lab reports to real-world journal publications.

Synthesis and Analysis of Zinc Copper Indium Sulfide Quantum Dot Nanoparticles

“…The effective mass model ,,,,,, suggests where E g = hc /λ, r is the radius of the nanoparticle, and the constants and values for CuInS 2 are given in Box . The second term is the particle-in-a-box confinement energy for an electron–hole pair in a spherical QD, and the third term is the Coulomb attraction between an electron and hole modified by the screening of charges by the crystal.…”

“…This fundamental nanochemistry concept has been frequently illustrated in this Journal . Laboratory experiments using QDs have made use of CdSe, − CdS, ,− ZnO, , C, , PbS, , Cu 2 O, and CsPbX 3 . QDs are an intriguing material for applications in solar cells, , in video displays, as hydrolysis photocatalysts, in white LED lighting, in photoluminescent labeling for bioimaging, and for cancer treatment .…”

“…Many QD synthesis procedures involve injecting a cooler solution of some of the reagents into a hot solution of the remaining reagents. ,,,, This method has the advantage of creating many nucleation sites to promote small particle sizes but the disadvantage of requiring rapid and homogeneous mixing. An alternative method, where decomposition of one component produces the limiting reactant, ,,,, requires rapid heating to again produce large numbers of nucleation sites in a short period of time.…”

Synthesis and Characterization of Nanoselenium: A Step-by-Step Guide for Undergraduate Students

“…There is a tremendous increase in the applications of SeNPs. Se and Se-containing NPs have been extensively used as semiconductive material. , SeNPs are also used in catalytic reduction of industrial pollutants such as methylene blue, methyl orange, etc. These are also widely used as dietary supplements in aquaculture for providing enriched diets to marine bodies .…”

“…Pharmacologically active molecules present in different parts of the plants, such as leaves, stem, bark, seeds, fruit, roots, etc., help in reducing the metal salts into metal/metal oxide nanoparticles . Microbial proteins and enzymes have also been exploited for synthesizing selenium nanoparticles. , Se and Se-containing NPs have various applications such as in diagnostics due to their optical and semiconductor properties; − as a template for optoelectronic devices; as anticancer, − antioxidant, − antimicrobial, ,, and antiarthritic agents; as nutrient supplements; , and also as degrading agents for organic dyes. ,, …”