Copper Indium Sulfide Quantum Dots Research Articles

Direct Synthesis and Characterization of Hydrophilic Cu-Deficient Copper Indium Sulfide Quantum Dots.

Copper indium sulfide (CIS) nanocrystals constitute a promising alternative to cadmium- and lead-containing nanoparticles. We report a synthetic method that yields hydrophilic, core-only CIS quantum dots, exhibiting size-dependent, copper-deficient composition and optical properties that are suitable for direct coupling to biomolecules and nonradiative energy transfer applications. To assist such applications, we complemented previous studies covering the femtosecond-picosecond time scale with the investigation of slower radiative and nonradiative processes on the nanosecond time scale, using both time-resolved emission and transient absorption. As expected for core particles, relaxation occurs mainly nonradiatively, resulting in low, size-dependent photoluminescence quantum yield. The nonradiative relaxation from the first excited band is wavelength-dependent with lifetimes between 25 and 150 ns, reflecting the size distribution of the particles. Approximately constant lifetimes of around 65 ns were observed for nonradiative relaxation from the defect states at lower energies. The photoluminescence exhibited a large Stokes shift. The band gap emission decays on the order of 10 ns, while the defect emission is further red-shifted, and the lifetimes are on the order of 100 ns. Both sets of radiative lifetimes are wavelength-dependent, increasing toward longer wavelengths. Despite the low radiative quantum yield, the aqueous solubility and long lifetimes of the defect states are compatible with the proposed role of CIS quantum dots as excitation energy donors to biological molecules.

Copper Indium Sulfide Quantum Dots as Nanomanometers: Influence of Size and Composition

AbstractMechanical forces control the function of organisms and mediate the interaction between biological systems and their environments. Knowledge of these forces will increase the understanding of biological processes and can support the development of novel diagnostic and therapeutic procedures. Although techniques like atomic force microscopy and droplet insertion method allow measuring forces over a broad range of values, they are invasive and lack versatility. A promising way to overcome these hurdles is luminescent nanomanometry. Quantum dots (QDs) specifically have optical properties that depend on their size because of the quantum confinement, which makes them responsive to applied forces. Yet, a fine understanding of how fundamental parameters affect the response to applied stress is required before a QD family can be credibly proposed as luminescent nanomanometers. Here, a thorough study is conducted on how size and stoichiometry affect the nanomanometry performance of CuInS2 QDs. The studied QDs feature pressure‐dependent photoluminescence in the red/near‐infrared range, which can enable the measurement of mechanical forces in the range of physiological relevance in a remote and minimally invasive way. It is shown that tuning size and stoichiometry can simultaneously enhance the CuInS2 QDs’ brightness and response to applied pressure, thus providing guidelines for better luminescent nanomanometers.

Improving Organic Photovoltaic Efficiency via Heterophase Homojunction Copper Indium Sulfide Nanocrystals

Eco‐friendly heterophase homojunction copper indium sulfide quantum dots (HH‐CIS QDs) terminated by short hydroxyl ligands are integrated into nonfullerene organic solar cells (OSCs) for the first time. Experimental results exhibit that this novel nanostructure can improve sunlight absorption and charge transfer ability, harvesting more photons and converting them to charge carriers. Additionally, the formation of hydrogen bonds between 2‐mercaptoethanol‐capped HH‐CIS QDs and the interface modification layer is beneficial for better interfacial contact, which promotes work function modification, reduces surface roughness, and increases interfacial charge transfer. Benefiting from HH‐CIS QDs incorporation, nonfullerene OSCs involving two different types of photoactive layers and three different types of electron transport layers all demonstrate improved photoelectric conversion efficiency (PCE). With QDs concentration optimization, nonfullerene OSCs with the PM6:ITIC‐4F and PM6:Y6 absorbers exhibit excellent PCEs of 14.04% and 16.26%, respectively. As compared to those reported previously, HH‐CIS QDs into the interface between the electron charge layer and photoactive layer lead to significant performance improvement, with both achieve PCEs and enhancement factors among the highest ones reported for various QD‐integrated OSCs. The results strongly suggest that the rational design of QDs and their optimal integration are critical for performance enhancement.

Single-Particle Dynamics of ZnS Shelling Induced Replenishment of Carrier Diffusion for Individual Emission Centers in CuInS2 Quantum Dots.

Insights into blinking and photoactivation of aqueous copper indium sulfide (CIS) quantum dots have been obtained using fluorescence correlation spectroscopy (FCS) and fluorescence lifetime correlation spectroscopy (FLCS). An unusual excitation wavelength-dependence of photoactivation/photocorrosion is manifested in an increase in the initial correlation amplitude G(0) for λex = 532 nm, but a decrease for λex = 405 nm. This has been rationalized in terms of different contributions from surface-assisted recombination in the two cases. Blinking times obtained from the autocorrelation functions (ACFs) of the 100-200 ns lifetime component (core Cu-mediated recombination) are almost unaffected by shelling, but those from the ACF for the 10-30 ns lifetime (surface states) increase significantly. Absence of cross-correlation between the two recombinative states of bare CIS QDs and the emergence of an anticorrelation with the introduction of the ZnS shell are observed, indicating the diffusive nature of the two states for CIS-ZnS. The diffusion is inhibited in bare CIS QDs due to the preponderance of surface states.

Light-harvesting antennae based on copper indium sulfide (CIS) quantum dots.

Copper indium sulfide quantum dots (CIS QDs) and their core-shell analogues (CIS@ZnS QDs) were functionalized with pyrene chromophores via a dihydrolipoamide bifunctional binding moiety: UV excitation of the pyrene chromophores resulted in sensitized emission of the CIS core because of an efficient energy transfer process; the core-shell hybrid system exhibits a 50% increased brightness when excited at 345 nm.

Unraveling the Emission Pathways in Copper Indium Sulfide Quantum Dots.

Semiconductor copper indium sulfide quantum dots are emerging as promising alternatives to cadmium- and lead-based chalcogenides in solar cells, luminescent solar concentrators, and deep-tissue bioimaging due to their inherently lower toxicity and outstanding photoluminescence properties. However, the nature of their emission pathways remains a subject of debate. Using low-temperature single quantum dot spectroscopy on core-shell copper indium sulfide nanocrystals, we observe two subpopulations of particles with distinct spectral features. The first class shows sharp resolution-limited emission lines that are attributed to zero-phonon recombination lines of a long-lived band-edge exciton. Such emission results from the perfect passivation of the copper indium sulfide core by the zinc sulfide shell and points to an inversion in the band-edge hole levels. The second class exhibits ultrabroad spectra regardless of the temperature, which is a signature of the extrinsic self-trapping of the hole assisted by defects in imperfectly passivated quantum dots.

Luminescent copper indium sulfide (CIS) quantum dots for bioimaging applications.

Copper indium sulfide (CIS) quantum dots are ideal for bioimaging applications, by being characterized by high molar absorption coefficients throughout the entire visible spectrum, high photoluminescence quantum yield, high tolerance to the presence of lattice defects, emission tunability from the red to the near-infrared spectral region by changing their dimensions and composition, and long lifetimes (hundreds of nanoseconds) enabling time-gated detection to increase signal-to-noise ratio. The present review collects: (i) the most common procedures used to synthesize stable CIS QDs and the possible strategies to enhance their colloidal stability in aqueous environment, a property needed for bioimaging applications; (ii) their photophysical properties and parameters that affect the energy and brightness of their photoluminescence; (iii) toxicity and bioimaging applications of CIS QDs, including tumor targeting, time-gated detection and multimodal imaging, as well as theranostics. Future perspectives are analyzed in view of advantages and potential limitations of CIS QDs compared to most traditional QDs.

Revealing Exciton and Metal–Ligand Conduction Band Charge Transfer Absorption Spectra in Cu-Zn-In-S Nanocrystals

Copper indium sulfide quantum dots (QDs) have attracted substantial attention in recent years due to environmental issues and diverse applications. We report the synthesis and characterization of c...

A highly sensitive chemiluminescence assay for diniconazole by using CuInS2 quantum dots

We demonstrate here the first use of water-soluble copper indium sulfide quantum dots (CuInS2 QDs) as the chemiluminescence (CL) reagent and its application to the highly sensitive detection of diniconazole. We utilized a hydrothermal method for synthesis of mercaptopropionic acid-capped CuInS2 QDs, which were characterized by TEM image, EDS, and XRD pattern. The performance of these QDs as the CL reagent was investigated by using several oxidizing agents and found that acidic potassium permanganate (KMnO4) gave the highest CL signal. CuInS2 QDs/KMnO4 as a novel CL probe was then used for assay of diniconazole based on its unique enhancing effect. In the optimum settings, a linear calibration plot was obtained for diniconazole in the concentration range of 4.0 × 10−9 mol L−1–1.5 × 10−6 mol L−1, with a limit of detection of 1.0 × 10−9 mol L−1. The study of interferences and recoveries confirmed the suitability of the method for assay of environmental water samples.

High‐performance HTL‐free perovskite solar cell: An efficient composition of ZnO NRs, RGO, and CuInS2 QDs, as electron‐transporting layer matrix

AbstractA hole‐transporting layer (HTL)‐free perovskite solar cell (PSC) with fluorine‐doped tin oxide (FTO)/nanocomposite electron‐transporting layer (ETL)/perovskite/Au structure is presented that takes advantage of a novel ternary nanocomposite constructed of zinc oxide (ZnO) nanorods, reduced graphene oxide (RGO), and copper indium sulfide quantum dots (CuInS2 QDs), as ETL. Concisely, the photoelectric and photovoltaic properties of all the individual, binary, and ternary composites were monitored by using of the photoluminescence (PL) spectroscopy, UV‐visible (vis) spectroscopy, J‐V curves, and incident photon‐to‐current conversion efficiency (IPCE) spectra studies. The comparative values exhibited a noticeable benefit for the ZnO‐RGO5%‐CuInS220% ternary nanocomposite as an appropriate ETL for PCS. Also, the comparative structural studies on the individual nanoscale components, binary, and ternary nanocomposite (with different percentages of CuInS2 QDs) were precisely performed by Fourier transform infrared (FT‐IR), energy‐dispersive X‐ray (EDX), X‐ray diffraction (XRD), Raman spectroscopy, and field emission scanning electron microscopy (FESEM), as well. Overall, after careful optimization of the ETL, a15.74% efficiency was resulted through applying the prepared ZnO‐RGO5%‐CuInS220% composite in a HTL‐free PCS with 0.33 cm2 active area.

CuInS2 Quantum Dots with Thick ZnSexS1–x Shells for a Luminescent Solar Concentrator

The photoluminescence quantum yield (PLQY) of copper indium sulfide (CIS) quantum dots (QDs) improves significantly after a shelling procedure as the shell materials, like zinc sulfide, mitigate surface defects and reduce nonradiative recombinations. However, it is widely observed that the PLQY reduces when QDs are cast as a solid film from their solution, and PL peak emission also red-shifts, which suggests a relaxation of the quantum confinement effect. This could be due to thin zinc sulfide shells. Unlike cadmium-based QDs, reports on a thick zinc chalcogenide shell on CIS QDs are limited. Efforts to grow larger shells have been stymied by zinc diffusion toward the core, causing cation exchange and alloy formation. Thick zinc chalcogenide shell growth typically requires higher temperatures, a regime which would irreversibly degrade the PL of a CIS QD. Here, we develop a technique to grow thicker shells on CIS QDs to improve the quantum confinement effect between the QDs. With these thick shell CIS QDs, we demonstrate better emission as well as thermal and chemical stability. Finally, we demonstrate their application in a luminescent solar concentrator and showed that it has better light harvesting characteristics than its thin shell counterpart.

Preliminary Study of Effective Copper Indium Sulfide (CuInS2) Quantum Dots as Photo-sensitizer in Solar Cell

Recent studies showed that quantum dots (QDs) materials such as cadmium (Cd) and lead (Pb) are commonly used as sensitizer in solar cell applications. This is mainly because they have high potential in light harvesting. However, these materials are highly toxicity and very harmful to the environment. Therefore, current investigation reports the performance of quantum dots sensitized solar cells (QDSSCs) based on non-toxicity CuInS<sub>2</sub> QDs by using solvothermal process. TiO<sub>2</sub> paste were deposited by doctor blade method on transparent conducting fluorine doped tin oxide (FTO) glass substrates. The CuInS<sub>2</sub> nano sized QDs were controlled by different solvothermal reaction times of 2 hours, 4 hours, 6 hours and 8 hours. In this study, the morphology, structural and optical properties of prepared TiO<sub>2</sub>/CuInS<sub>2</sub> QDs thin films were investigated by using Transmission Electron Microscope (TEM), Atomic Force Microscope (AFM), X-ray Diffraction (XRD) and Ultra-Violet-Visible Near Infrared Spectrophotometer (UV-Vis). The diameter of CuInS<sub>2</sub> QDs was found to be increased from 3.19 nm to 8.67 nm with longer reaction time. Results showed that CuInS<sub>2</sub> QDs with longer reaction time produced higher conversion efficiency. Based on the experiment done, CuInS<sub>2</sub> QDs with 8 hours reaction time produced the best power conversion efficiency; 0.035 %. Regarding the considerable efficiencies obtained, pointed out that CuInS<sub>2</sub> QDs can be introduced as an effective photosensitizer for making efficient QDSSCs devices.

Preparation of highly emissive and reproducible Cu–In–S/ZnS core/shell quantum dots with a mid-gap emission character

Copper indium sulfide (CIS) quantum dots (QDs) are one of the newest types of luminescent semiconductors with low-toxicity and earth-abundant features. The present work reports the successful aqueous synthesis of CIS/ZnS core/shell QDs using dual-stabilizing agents of N-acetyl-l-cysteine and trisodium citrate. Off-stoichiometric QDs with In-rich compositions were found to be very small and highly emissive after coating by a shell of wide bandgap ZnS. The effect of various experimental parameters was evaluated to achieve highly reproducible QDs with bright reddish emission. Results showed a significant contribution of mid-gap defect states in the recombination processes (based on the gradual increase in absorbance recorded for samples, relatively high Urbach energy, large Stokes shift, large FWHM value in PL spectra, as well as the long-lived PL decay time). In addition, the chemical stability of samples was investigated using highly oxidant H2O2 agent and results demonstrate their superior stability. The combination of low-toxicity, intense and stable emission, along with synthetic advantages demonstrates that the present aqueous-soluble and emissive QDs can be considered as an excellent bio-photonic structure suitable for different fields of biological imaging and diagnostics.

Spectroscopic and Magneto-Optical Signatures of Cu1+ and Cu2+ Defects in Copper Indium Sulfide Quantum Dots.

Colloidal quantum dots (QDs) of I-III-VI ternary compounds such as copper indium sulfide (CIS) and copper indium selenide (CISe) have been under intense investigation due to both their unusual photophysical properties and considerable technological utility. These materials feature a toxic-element-free composition, a tunable bandgap that covers near-infrared and visible spectral energies, and a highly efficient photoluminescence (PL) whose spectrum is located in the reabsorption-free intragap region. These properties make them attractive for light-emission and light-harvesting applications including photovoltaics and luminescent solar concentrators. Despite a large body of literature on device-related studies of CISe(S) QDs, the understanding of their fundamental photophysical properties is surprisingly poor. Two particular subjects that are still heavily debated in the literature include the mechanism(s) for strong intragap emission and the reason(s) for a poorly defined (featureless) absorption edge, which often "tails" below the nominal bandgap. Here, we address these questions by conducting comprehensive spectroscopic studies of CIS QD samples with varied Cu-to-In ratios using resonant PL and PL excitation, femtosecond transient absorption, and magnetic circular dichroism measurements. These studies reveal a strong effect of stoichiometry on the concentration of Cu1+ vs Cu2+ defects (occurring as CuIn″ and CuCu• species, respectively), and their effects on QD optical properties. In particular, we demonstrate that the increase in the relative amount of Cu2+ vs Cu1+ centers suppresses intragap absorption associated with Cu1+ states and sharpens band-edge absorption. In addition, we show that both Cu1+ and Cu2+ centers are emissive but are characterized by distinct activation mechanisms and slightly different emission energies due to different crystal lattice environments. An important overall conclusion of this study is that the relative importance of the Cu2+ vs Cu1+ emission/absorption channels can be controlled by tuning the Cu-to-In ratio, suggesting that the control of sample stoichiometry represents a powerful tool for achieving functionalities (e.g., strong intragap emission) that are not accessible with ideal, defect-free materials.

Zinc Thiolate Enables Bright Cu-Deficient Cu-In-S/ZnS Quantum Dots.

Copper indium sulfide (CIS) colloidal quantum dots (QDs) are a promising candidate for commercially viable QD-based optical applications, for example as colloidal photocatalysts or in luminescent solar concentrators (LSCs). CIS QDs with good photoluminescence quantum yields (PLQYs) and tunable emission wavelength via size and composition control are previously reported. However, developing an understanding and control over the growth of electronically passivating inorganic shells would enable further improvements of the photophysical properties of CIS QDs. To improve the optical properties of CIS QDs, the focus is on the growth of inorganic shells via the popular metal-carboxylate/alkane thiol decomposition reaction. 1) The role of Zn-carboxylate and Zn-thiolate on the formation of ZnS shells on Cu-deficient CIS (CDCIS) QDs is studied, 2) this knowledge is leveraged to yield >90% PLQY CDCIS/ZnS core/shell QDs, and 3) a mechanism for ZnS shells grown from zinc-carboxylate/alkane thiol decomposition is proposed.

Biocompatible off-stoichiometric copper indium sulfide quantum dots with tunable near-infrared emission via aqueous based synthesis.

The present study reports an aqueous synthesis approach towards off-stoichiometric copper indium sulfide quantum dots with emissions in the near-infrared spectral range. The photoluminescence properties of the dots, and in particular the appearance of dual emission at high Cu deficiency, were studied with temperature-dependent steady-state and transient photoluminescence spectroscopy.

Femtosecond two-photon absorption spectroscopy of copper indium sulfide quantum dots: A structure-optical properties relationship

We have interpreted the two-photon absorption spectrum of water-soluble copper indium sulfide (CIS) QDs with stoichiometry 0.18 (Cu), 0.42 (In), and 2 (S) and an average diameter of approximately 2.6 nm. For that, we employed the wavelength-tunable femtosecond Z-scan technique and the parabolic effective-mass approximation model, in which the excitonic transition energies were phenomenologically corrected due to the stoichiometry of the nanocrystal. This model considers a conduction band and three valence sub-bands allowing excitonic transitions via centrosymmetric (Δl = ±1, where l is the angular momentum of the absorbing state) and non-centrosymmetric (Δl = 0) channels. In such case, this became relevant because the CIS QDs with chalcopyrite crystalline structure is a non-centrosymmetric semiconductor. Thus, our experimental results pointed out two 2 PA allowed bands located at 715 nm (2hv = 3.47 eV) and 625 nm (2hv = 3.97 eV) with cross sections of (6.3 ± 1.0) x 102 GM and (4.5 ± 0.7) x 102 GM, respectively. According to the theoretical model, these 2 PA bands can be ascribed to the 1P1/2(h3) → 1S3/2(e) (lower energy band) and 1P1/2(hheavy) → 1S3/2(e) (90%)/(10%)1P1/2(hsplit-off) → 1P3/2(e) (higher energy band) excitonic transitions. A good agreement (magnitude and spectral position) between the experimental and theoretical data were obtained. However, our experimental data suggest that the higher-energy 2 PA band may have other contributions due to the mixing between the heavy- and the light-hole bands, which the effective mass model does not take into consideration.

Dependence of the Photoluminescence of Hydrophilic CuInS2 Colloidal Quantum Dots on Cu-to-In Molar Ratios

Copper indium sulfide (CIS) quantum dots (QDs) are attractive as potential optoelectronic devices, since they have large absorption coefficients across a broad spectral range, size- and composition-tunable photoluminescence from the visible to the near-infrared, and low toxicity. However, CIS QDs should be hydrophilic in certain applications. In this present work, hydrophilic CIS and CIS/ZnS colloidal QDs were synthesized by a one-pot environmentally-friendly route employing N,N-dimethylformamide (DMF) as the solvent and in situ generated H2S as the sulphur precursor. The effect of stoichiometry was investigated by varying the feeding molar ratios of Cu/In, which did not affect the crystalline structure of the CIS colloidal QDs, while the optical property was influenced significantly. With the decrease of the feeding molar ratios of Cu/In, the band gap of the resulting CIS colloidal QDs had blue-shifts and relative photoluminescence quantum yield of the corresponding CIS/ZnS colloidal QDs increased monotonically.

Deep-red emitting zinc and aluminium co-doped copper indium sulfide quantum dots for luminescent solar concentrators

Pure CuInS2 quantum dots (CIS QDs) exhibited poor photoluminescent (PL) performance due to more dangling bonds on their surface and thus needed a shell to form core@shell structured QDs. However, conventional shells had a higher band gap than CIS QDs so that the core@shell structured QDs showed a blue-shifted PL peak below 700 nm and narrower light absorption range. Herein, Zn and Al co-doped CIS QDs were synthesized by a facile cation exchanged method which can significantly improve the PL property emitting at ∼740 nm compared to pure CIS QDs. The enhancement of the PL property was probably attributed to ZnCu and AlCu defects in the CIS QDs which could cause electron-hole radiative recombination via defect levels, reduce the number of dangling bonds and thus minimize the nonradiative recombination through surface electron trapping. Furthermore, the PL intensity was controlled by doping time and reached the maximum at 30 min. The obtained deep-red emitting CIS QDs were employed to fabricate semi-transparent luminescent solar concentrators (LSCs) which exhibited an excellent optical efficiency of 6.97%. The success in using such Zn and Al co-doped CIS QDs could pave the way to realize high efficiency and environment-friendly LSCs for building integrated photovoltaics.

Luminescence and photoelectrochemical properties of size-selected aqueous copper-doped Ag-In-S quantum dots.

Ternary luminescent copper and silver indium sulfide quantum dots (QDs) can be an attractive alternative to cadmium and lead chalcogenide QDs. The optical properties of Cu–In–S and Ag–In–S (AIS) QDs vary over a broad range depending on the QD composition and size. The implementation of ternary QDs as emitters in bio-sensing applications can be boosted by the development of mild and reproducible syntheses directly in aqueous solutions as well as the methods of shifting the photoluminescence (PL) bands of such QDs as far as possible into the near IR spectral range. In the present work, the copper-doping of aqueous non-stoichiometric AIS QDs was found to result in a red shift of the PL band maximum from around 630 nm to ∼780 nm and PL quenching. The deposition of a ZnS shell results in PL intensity recovery with the highest quantum yield of 15%, with almost not change in the PL band position, opposite to the undoped AIS QDs. Size-selective precipitation using 2-propanol as a non-solvent allows discrimination of up to 9 fractions of Cu-doped AIS/ZnS QDs with the average sizes in the fractions varying from around 3 to 2 nm and smaller and with reasonably the same composition irrespective of the QD size. The decrease of the average QD size results in a blue PL shift yielding a series of bright luminophors with the emission color varies from deep-red to bluish-green and the PL efficiency increases from 11% for the first fraction to up to 58% for the smallest Cu-doped AIS/ZnS QDs. The rate constant of the radiative recombination of the size-selected Cu-doped AIS/ZnS QDs revealed a steady growth with the QD size decrease as a result of the size-dependent enhancement of the spatial exciton confinement. The copper doping was found to result in an enhancement of the photoelectrochemical activity of CAIS/ZnS QDs introduced as spectral sensitizers of mesoporous titania photoanodes of liquid-junction solar cells.