Machado W, Wegner KD, Gontijo LAP, Bettini J, Schiavon MA, Reiss P, Aldakov D. Hydrothermal Synthesis of Aqueous-Soluble Copper Indium Sulfide Nanocrystals and Their Use in Quantum Dot Sensitized Solar Cells

A facile hydrothermal method to synthesize water-soluble copper indium sulfide (CIS) nanocrystals (NCs) at 150 °C is presented. The obtained samples exhibited three distinct photoluminescence peaks in the red, green and blue spectral regions, corresponding to three size fractions, which could be separated by means of size-selective precipitation. While the red and green emitting fractions consist of 4.5 and 2.5 nm CIS NCs, the blue fraction was identified as in situ formed carbon nanodots showing excitation wavelength dependent emission. When used as light absorbers in quantum dot sensitized solar cells, the individual green and red fractions yielded power conversion efficiencies of 2.9% and 2.6%, respectively. With the unfractionated samples, the efficiency values approaching 5% were obtained. This improvement was mainly due to a significantly enhanced photocurrent arising from complementary panchromatic absorption.

Bandgap Tunable Ternary Cd x Sb2-y S3-δ Nanocrystals for Solar Cell Applications

We report the synthesis and photovoltaic performance of a new nonstoichiometric ternary metal sulfide alloyed semiconductor-Cd _x Sb_2-y S_3-δ nanocrystals prepared by the two-stage sequential ionic layer adsorption reaction technique. The synthesized Cd _x Sb_2-y S_3-δ nanocrystals retain the orthorhombic structure of the host Sb₂S₃ with Cd substituting a fraction (x = 0-0.15) of the cationic element Sb. The Cd _x Sb_2-y S_3-δ lattice expands relative to the host, Sb₂S_3, with its lattice constant a increasing linearly with Cd content x. Optical and external quantum efficiency (EQE) spectra revealed that the bandgap E _g of Cd _x Sb_2-y S_3-δ decreased from 1.99 to 1.69 eV (i.e., 625-737 nm) as x increased from 0 to 0.15. Liquid-junction Cd _x Sb_2-y S_3-δ quantum dot-sensitized solar cells were fabricated using the polyiodide electrolyte. The best cell yielded a power conversion efficiency (PCE) of 3.72% with the photovoltaic parameters of J _sc = 15.97 mA/cm², V _oc = 0.50 V, and FF = 46.6% under 1 sun. The PCE further increased to 4.86%, a respectable value for a new solar material, under a reduced light intensity of 10% sun. The PCE (4.86%) and J _sc (15.97 mA/cm²) are significantly larger than that (PCE = 1.8%, J _sc = 8.55 mA/cm²) of the Sb₂S₃ host. Electrochemical impedance spectroscopy showed that the ZnSe passivation coating increased the electron lifetime by three times. The EQE spectrum of Cd _x Sb_2-y S_3-δ has a maximal EQE of 82% at λ = 350 nm and covers the spectral range of 300-750 nm, which is significantly broader than that (300-625 nm) of the Sb₂S₃ host. The EQE-integrated current density yields a J _ph of 11.76 mA/cm². The tunable bandgap and a respectable PCE near 5% suggest that Cd _x Sb_2-y S_3-δ could be a potential candidate for a solar material.

Enzymatic biomineralization of biocompatible CuInS2, (CuInZn)S2 and CuInS2/ZnS core/shell nanocrystals for bioimaging

This work demonstrates a bioenabled fully aqueous phase and room temperature route to the synthesis of CuInS₂/ZnS core/shell quantum confined nanocrystals conjugated to IgG antibodies and used for fluorescent tagging of THP-1 leukemia cells. This elegant, straightforward and green approach avoids the use of solvents, high temperatures and the necessity to phase transfer the nanocrystals prior to application. Non-toxic CuInS₂, (CuInZn)S₂, and CuInS₂/ZnS core/shell quantum confined nanocrystals are synthesized via a biomineralization process based on a single recombinant cystathionine γ-lyase (CSE) enzyme. First, soluble In-S complexes are formed from indium acetate and H₂S generated by CSE, which are then stabilized by l-cysteine in solution. The subsequent addition of copper, or both copper and zinc, precursors then results in the immediate formation of CuInS₂ or (CuInZn)S₂ quantum dots. Shell growth is realized through subsequent introduction of Zn acetate to the preformed core nanocrystals. The size and optical properties of the nanocrystals are tuned by adjusting the indium precursor concentration and initial incubation period. CuInS₂/ZnS core/shell particles are conjugated to IgG antibodies using EDC/NHS cross-linkers and then applied in the bioimaging of THP-1 cells. Cytotoxicity tests confirm that CuInS₂/ZnS core/shell quantum dots do not cause cell death during bioimaging. Thus, this biomineralization enabled approach provides a facile, low temperature route for the fully aqueous synthesis of non-toxic CuInS₂/ZnS quantum dots, which are ideal for use in bioimaging applications.

Optoelectronic Properties of CuInS2 Nanocrystals and Their Origin

The capacity of fluorescent colloidal semiconductor nanocrystals for commercial application has led to the development of nanocrystals with nontoxic constituent elements as replacements for the currently available Cd- and Pb-containing systems. CuInS2 is a good candidate material because of its direct band gap in the near-infrared spectral region and large optical absorption coefficient. The ternary nature, flexible stoichiometry, and different crystal structures of CuInS2 lead to a range of optoelectronic properties, which have been challenging to elucidate. In this Perspective, the optoelectronic properties of CuInS2 nanocrystals are described and what is known of their origin is discussed. We begin with an overview of their synthesis, structure, and mechanism of formation. A complete discussion of the tunable luminescence properties and the radiative decay mechanism of this system is then presented. Finally, progress toward application of these "green" nanocrystals is summarized.

Air-exposing microwave-assisted synthesis of CuInS2/ZnS quantum dots for silicon solar cells with enhanced photovoltaic performance

CIS/ZnS QDs were synthesized by microwave irradiation in air. The fabricated QDs/PMMA composite films were first applied to Si solar cells to improve the conversion efficiency by 3.8%.

Low-cost and gram-scale synthesis of water-soluble Cu-In-S/ZnS core/shell quantum dots in an electric pressure cooker

We report an electric pressure cooker for large-scale synthesis of water-soluble Cu-In-S/ZnS core/shell quantum dots. Low-cost thioglycolic acid and sodium citrate were used as the dual stabilizers. ∼3 grams of quantum dots with a tunable emission from 545 to 610 nm and quantum yield up to 40% were obtained in a batch.

Synthesis and application of colloidal CuInS2 semiconductor nanocrystals

Semiconductor nanocrystals possess size-dependent properties, which make them interesting candidates for a variety of applications, e.g., in solar energy conversion, lighting, display technology, or biolabelling. However, many of the best studied nanocrystalline materials contain toxic heavy metals; this seriously limits their potential for widespread application. One of the possible less toxic alternatives to cadmium- or lead-containing semiconductors is copper indium disulfide (CIS), a direct semiconductor with a bandgap in the bulk of 1.45 eV and a Bohr exciton radius of 4.1 nm. This Review gives an overview of the methods developed during the last years to synthesize CIS nanocrystals and summarizes the possibilities to influence their shape, composition and crystallographic structure. Also the potential of the application of CIS nanocrystals in biolabellling, photocatalysis, solar energy conversion, and light-emitting devices is discussed.

Aqueous synthesis of color-tunable CuInS2/ZnS nanocrystals for the detection of human interleukin 6

In this Article, we present a facile microwave-assisted synthesis route for the preparation of water-soluble and high-quality CuInS2/ZnS nanocrystals (NCs) with glutathione as the stabilizer. The as-prepared CuInS2/ZnS NCs exhibited small particle sizes (~3.3 nm), long photoluminescence lifetimes, and color-tunable properties ranging from the visible to the near-infrared by varying the initial ratio of Cu/In in the precursors. The low-toxicity, highly luminescent and biocompatible CuInS2/ZnS NCs were applied to cell imaging, showing that they could be used as promising fluorescent probes. Furthermore, the CuInS2/ZnS NCs were used as the signal labels for a fluoroimmunoassay of the biomarker IL-6, showing their great potential for use as reliable point-of-care diagnostics for biomarkers of cancer and other diseases.