CuInS2 Quantum Dots Research Articles

Influence of ZnO nano-array interlayer on the charge transfer performance of quantum dot sensitized solar cells

Single crystalline ZnO nano-array films are prepared by electrochemical deposition process, which are successfully introduced as an interlayer between FTO conductive glass substrate and TiO2 nanoparticle films to fabricate the quantum dot sensitized solar cells. Different structure of ZnO nano-array films are modulated by the time of electrochemical deposition process, which have been mainly investigated the photovoltaic performance and charge transfer property of the solar cells. The enhancements of optical absorption properties and electron-hole separation properties on photo-electrodes have been observed by UV–Vis absorption and photoluminescence spectra. And electrochemical impedance spectra and photoluminescence decay analysis have indicated that the ZnO nano-array interlayer can effectively increase the rate of charge transfer in the quantum dot sensitized solar cells system. With the balance on the diameter, density and thickness of the ZnO nano-array interlayer, the photovoltaic conversion efficiency of FTO/ZnO/TiO2/CuInS2 quantum dot sensitized solar cells have enhanced from 4.12% to 4.58% without any optimization of passivation, electrolyte and counter electrode.

Aqueous synthesis of Mn-doped CuInSe2 quantum dots to enhance the performance of quantum dot sensitized solar cells.

Herein, we present the direct aqueous synthesis of manganese (Mn) doped CuInSe2 (Mn-CISe) quantum dots (QDs) under microwave irradiation to improve the photochemical properties of solar cells. As a result of Mn doping, the narrower bandgap energy of Mn-CISe leads to higher visible light absorption. The Mn-CISe QDs are therefore used as photosensitizers in quantum dot sensitized solar cells (QDSSCs), exhibiting enhanced performance which is dependent on Mn concentration. To the best of our knowledge, this is the first time to construct an Mn-CISe sensitized-TiO2 photoanode to boost the photovoltaic performance of QDSSCs. The incorporation of Mn into CISe increases short-circuit current, which is ascribed to the effective injection of the excited electrons from QDs into TiO2 and the consequent higher electron lifetime, likely through a newly formed Mn midgap in the CISe band structure. Compared to the undoped QDs, Mn-CISe QDSSCs show a shorter electron transport time (τt) and a longer electron recombination time (τr) which are studied by intensity-modulated photocurrent spectroscopy and intensity-modulated photovoltage spectroscopy, respectively. In fact, a combination of higher light-harvesting efficiency, slower charge recombination, and a longer electron lifetime gives rise to a maximum photovoltaic performance of 6.28%.

Ligand Exchange Functionalization of CIS Quantum Dots for CIS/ZnO Film Heterojunctions

Colloidal quantum dots (QD) are rapidly making their way into several optoelectronic applications. While Cd- and Pb-based QDs are promising for high-performance devices, toxicity remains a concern. In this regard, Cu-In-S (CIS) QDs provide an alternative option for scalable, commercial production. A low-temperature, high-throughput process was used to synthesize CIS QDs with 1-dodecanethiol (DDT) ligands. While QD synthesis with a DDT ligand is facile, there are drawbacks when it comes to device implementation and interfacing with electron transport films such as ZnO. A ligand exchange process was employed to replace the DDT ligands in the as-synthesized QDs with 3-mercaptopropionic acid (MPA); owing to the short and bifunctional nature of the MPA molecules, this process improved the surface adhesion and carrier transport to ZnO. I-V measurements on planar structures showed the significance of ligand exchange in CIS QDs for heterojunction device implementation.

Combining evident photocurrent of photoanode with signal amplification of biocathode: toward a sensitivity and specificity enhanced photoelectrochemical immunosensor

Highly sensitive and specific detection of biomarkers is of great importance for diagnosis and treatment of the related diseases or cancers. We herein developed a robust photoelectrochemical (PEC) immunosensor with enhanced sensitivity and specificity based on evident photocurrent output of the photoanode and significant signal amplification of the biocathode. Prostate specific antigen (PSA, Ag) was used as a target model to exhibit analytical performances of the designed PEC immunosensor. Two kinds of CuInS2 quantum dots (CIS QDs) with different composition were modified on the TiO2 nanotubes (TiO2-NTs) electrode to fabricate the photoanode. Due to the co-sensitization effect of the CIS QDs on TiO2-NTs, an evident photocurrent output was generated at the photoanode. For the biocathode, Au nanoparticles (AuNPs) and polydopamine (PDA) were modified in order on indium-tin oxide (ITO) electrode to immobilize capture PSA antibody (Ab1). Carboxyl-modified polystyrene (PS) nanospheres were coated with secondary antibodies (Ab2) to form PS@Ab2 conjugates, which were used as signal amplifiers via the specific immunoreaction between Ag and Ab2. Based on joint action of evident photocurrent output of the photoanode and significant signal amplification of the biocathode, the designed PEC immunosensor exhibited an ultralow detection limit of 3.4 fg/mL for target PSA detection. Meanwhile, it also showed an enhanced specificity owing to the separation of the photoanode and the biocathode.

Facile Synthesis of Cu–In–S/ZnS Core/Shell Quantum Dots in 1-Dodecanethiol for Efficient Light-Emitting Diodes with an External Quantum Efficiency of 7.8%

CuInS2 quantum dots (QDs) are promising alternatives for user- and environment-friendly light-emitting diode (LED) applications, but the capping of electrically insulating ligands on QDs limits the device charge injection efficiency and results in poor LED performance. To solve the problem, in this work, we demonstrate the facile synthesis of Cu–In–S/ZnS (CIS/ZnS) core/shell QDs employing 1-dodecanethiol (DT) as the single ligand. The capping of QDs solely by DT not only enhances the colloidal stability of the QD ink by avoiding proton transfer between different kinds of ligands but also improves the electrical property of the QD films. By controlling the molar feed ratio of cations, the photoluminescence emission peak of the CIS/ZnS QDs is tunable from 530 to 710 nm. Because the QD surface chemistry is optimized, it becomes facile to perform QD surface modification for LED application. A QD LED prototype is fabricated using CIS/ZnS QDs as the emissive layer, which exhibits a maximum luminance of 4490 cd ...

CuInSe2 Quantum Dots Hybrid Hole Transfer Layer for Halide Perovskite Photodetectors.

A novel hybrid hole transport layer (HTL) of CuInSe2 quantum dots (QDs)/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) was developed to enhance the performance of halide metal perovskite (MAPbI3)-based photodetectors. The introduction of CuInSe2 QDs not only improved the wettability of the PEDOT:PSS HTL for the growth of perovskite crystals but also facilitated the transportation of holes from the perovskite to the HTL. As a result, both responsivity and detectivity of the device were increased dramatically by CuInSe2 QDs hybrid HTL, showing excellent photoresponsivity of 240 mA/W, larger ratio of photocurrent density to dark current density of 4.1 × 106, fast on-off switching properties of <0.02 s, and remarkable detectivity values of 1.02 × 1013 Jones at 580 nm and above 5.01 × 1012 Jones over the visible light region without an external bias voltage. In addition, the photodetectors also showed excellent thermal stability in the range of 10-110 °C. Therefore, a unique design idea of a hole transport material would be an anticipated direction for efficient halide metal perovskite-based devices.

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.

Evidence of Band-Edge Hole Levels Inversion in Spherical CuInS2 Quantum Dots.

CuInS2 (CIS) quantum dots (QDs) have emerged as one of the most promising candidates for application in a number of new technologies, mostly due to their heavy-metal-free composition and their unique optical properties. Among those, the large Stokes shift and the long-lived excited state are the most striking ones. Although these properties are important, the physical mechanism that originates them is still under debate. Here, we use two-photon absorption spectroscopy and ultrafast dynamics studies to investigate the physical origin of those phenomena. From the two-photon absorption spectroscopy, we observe yet another unique property of CIS QDs, a two-photon absorption transition below the one-photon absorption band edge, which has never been observed before for any other semiconductor nanostructure. This originates from the inversion of the 1S and 1P hole level order at the top of the valence band and results in a blue-shift of the experimentally measured one photon absorption edge by nearly 100 to 200 meV. However, this shift is not large enough to account for the Stokes shift observed, 200-500 meV. Consequently, despite the existence of the below band gap optical transition, photoluminescence in CIS QDs must originate from trap sites. These conclusions are reinforced by the multiexciton dynamics studies. From those, we demonstrate that biexciton Auger recombination behaves similarly to negative trion dynamics on these nanomaterials, which suggests that the trap state is an electron donating site.

Size-Dependent Band-Gap and Molar Absorption Coefficients of Colloidal CuInS2 Quantum Dots.

The knowledge of the quantum dot (QD) concentration in a colloidal suspension and the quantitative understanding of the size-dependence of the band gap of QDs are of crucial importance from both applied and fundamental viewpoints. In this work, we investigate the size-dependence of the optical properties of nearly spherical wurtzite (wz) CuInS2 (CIS) QDs in the 2.7 to 6.1 nm diameter range (polydispersity ≤10%). The QDs are synthesized by partial Cu+ for In3+ cation exchange in template Cu2–xS nanocrystals, which yields CIS QDs with very small composition variations (In/Cu = 0.91 ± 0.11), regardless of their sizes. These well-defined QDs are used to investigate the size-dependence of the band gap of wz CIS QDs. A sizing curve is also constructed for chalcopyrite CIS QDs by collecting and reanalyzing literature data. We observe that both sizing curves follow primarily a 1/d dependence. Moreover, the molar absorption coefficients and the absorption cross-section per CIS formula unit, both at 3.1 eV and at the band gap, are analyzed. The results demonstrate that the molar absorption coefficients of CIS QDs follow a power law at the first exciton transition energy (εE1 = 5208d2.45) and scale with the QD volume at 3.1 eV. This latter observation implies that the absorption cross-section per unit cell at 3.1 eV is size-independent and therefore can be estimated from bulk optical constants. These results also demonstrate that the molar absorption coefficients at 3.1 eV are more reliable for analytical purposes, since they are less sensitive to size and shape dispersion.

Fabrication and Photoelectrochemical Performance Optimization of CuInS2 Quantum Dots Sensitized TiO2 Nanonails Array Photoelectrodes

The CuInS2 quantum dots sensitization of TiO2 nanonails (NNs) array was successfully carried out by a successive ionic layer absorption and reaction (SILAR) method using CuCl2 ⋅ 2H2O, InCl3 ⋅ 4H2O and Na2S ⋅ 9H2O as precursors. The morphology, elemental composition and crystalline structure of the CuInS2 quantum dots sensitized TiO2 NNs array heterojunction nanostructures were characterized by field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), energy dispersive X-ray analysis (EDX), X-ray diffraction (XRD) and X-ray-photoelectron spectroscopy (XPS). The above characterization results could unanimously reveal that the nanoparticles successfully loaded on the TiO2 NNs array can be assigned as CuInS2 quantum dots. UV-Vis absorption measurements indicated that the CuInS2 quantum dots sensitization extended the visible light absorption. The largest short-circuit photocurrent density of 17.7[Formula: see text]mA/cm2 was obtained, which indicated that the CuInS2 was a promising material in activating visible light functionalities and enhancing photoelectrochemical performance.

Synthesis of CuInS2 Quantum Dots/In2S3/ZnO Nanowire Arrays with High Photoelectrochemical Activity

Decoration of CuInS2 (CIS) quantum dots (QDs) on ZnO nanowires (NWs) with an interlayer of In2S3 as photoelectrode has been successfully fabricated on FTO via the simple solution routes for photoelectrochemical (PEC) application. Scanning electron microscopy, transmission electron microscopy, and X-ray diffraction are utilized to systematically analyze the morphology and structure of the CIS QD/In2S3/ZnO NWs heterostructure. The composition of this multilayer heterostructure and the removal of QD ligands by a thermal process are confirmed by X-ray photoelectron spectra. In comparison with CIS QDs/ZnO NWs, the CIS QD/In2S3/ZnO heterostructural photoelectrode displays an efficient charge separation and carrier transport path for photocurrent up to 2.4 mA·cm–2 that is competitive with other Cd- and Pb-free QD-based materials. In addition, Mott–Schottky analysis demonstrates the negative shift of the flat band in the CIS QD/In2S3/ZnO, which benefits the early onset potential. Significantly, this hierarchical ...

Anisotropic 2D Cu2-x Se Nanocrystals from Dodecaneselenol and Their Conversion to CdSe and CuInSe2 Nanoparticles.

We present the synthesis of colloidal anisotropic Cu2–xSe nanocrystals (NCs) with excellent size and shape control, using the unexplored phosphine-free selenium precursor 1-dodecaneselenol (DDSe). This precursor forms lamellar complexes with Cu(I) that enable tailoring the NC morphology from 0D polyhedral to highly anisotropic 2D shapes. The Cu2–xSe NCs are subsequently used as templates in postsynthetic cation exchange reactions, through which they are successfully converted to CdSe and CuInSe2 quantum dots, nanoplatelets, and ultrathin nanosheets. The shape of the template hexagonal nanoplatelets is preserved during the cation exchange reaction, despite a substantial reorganization of the anionic sublattice, which leads to conversion of the tetragonal umangite crystal structure of the parent Cu2–xSe NCs into hexagonal wurtzite CdSe and CuInSe2, accompanied by a change of both the thickness and the lateral dimensions of the nanoplatelets. The crystallographic transformation and reconstruction of the product NCs are attributed to a combination of the unit cell dimensionalities of the parent and product crystal phases and an internal ripening process. This work provides novel tools for the rational design of shape-controlled colloidal anisotropic Cu2–xSe NCs, which, besides their promising optoelectronic properties, also constitute a new family of cation exchange templates for the synthesis of shape-controlled NCs of wurtzite CdSe, CuInSe2, and other metal selenides that cannot be attained through direct synthesis approaches. Moreover, the insights provided here are likely applicable also to the direct synthesis of shape-controlled NCs of other metal selenides, since DDSe may be able to form lamellar complexes with several other metals.

Improving on the interparticle connection for performance enhancement of flexible quantum dot sensitized solar cells

Flexible photovoltaic devices have wide applications in many unique areas. However, the interparticle connection of photo-electrode in flexible photovoltaic devices still needs to be improved. Here, TiO2 slurries have been prepared by a three-step process, which are employed to prepare the photo-anode for flexible CuInS2 quantum dot sensitized solar cells (QDSSCs). 5 nm-sized TiO2 nanoparticles and hydrochloric acid (HCl) have been introduced in 20 nm-sized TiO2 based photo-electrodes under TiO2/HCl mass ratio of 3:1, which exhibits excellent photovoltaic performance and charge transfer property. Due to the interparticle connection enhancement by suitable content of 5 nm-sized TiO2 nanoparticles, photo-anodes with the 20/5-TiO2 nanoparticles mass ratio of 3:1 exhibits the better optical absorption property and photovoltaic performance of flexible QDSSCs. Moreover, there has maintained 98% photovoltaic conversion efficiency of flexible QDSSCs with the seriously curving condition, which can be considered the great foreground in future applications.

Two-stage ZnS Shell Coating on the CuInS2 Quantum Dots for Their Effective Solubilization

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A novel fluorescent biosensor for adrenaline detection and tyrosinase inhibitor screening.

In this work, a novel simple fluorescent biosensor for the highly sensitive and selective detection of adrenaline was established. Firstly, water-soluble CuInS2 quantum dots (QDs) capped by L-Cys were synthesized via a hydrothermal synthesis method. Then, the positively charged adrenaline was assembled on the surface of CuInS2 QDs due to the electrostatic interactions and hydrogen bonding, which led to the formation of adrenaline-CuInS2 QD (Adr-CuInS2 QD) electrostatic complexes. Tyrosinase (TYR) can catalyze adrenaline to generate H2O2, and additionally oxidize the adrenaline to adrenaline quinone. Both the H2O2 and the adrenaline quinone can quench the fluorescence of the CuInS2 QDs through the electron transfer (ET) process. Thus, the determination of adrenaline could be facilely achieved by taking advantage of the fluorescence "turn off" feature of CuInS2 QDs. Under the optimum conditions, the fluorescence quenching ratio If/If0 (If and If0 were the fluorescence intensity of Adr-CuInS2 QDs in the presence and absence of TYR, respectively) was proportional to the logarithm of adrenaline concentration in the range of 1 × 10-8-1 × 10-4molL-1 with the detection limit of 3.6nmolL-1. The feasibility of the proposed biosensor in real sample assay was also studied and satisfactory results were obtained. Significantly, the proposed fluorescent biosensor can also be utilized to screen TYR inhibitors. Graphical abstract Schematic illustration of the fluorescent biosensor for adrenaline detection (A) and tyrosinase inhibitor screening (B).

Upconverting Nanoparticle to Quantum Dot Förster Resonance Energy Transfer: Increasing the Efficiency through Donor Design

We propose two effective approaches to enhance the Forster resonance energy transfer (FRET) efficiency from near-infrared excited upconverting nanoparticles (UCNPs, namely, LiYF4:Yb3+,Tm3+) to CuInS2 quantum dots (QDs) upon engineering of the donor’s architecture. The study of the particles’ interaction highlighted a radiative nature of the energy transfer among the moieties under investigation when in solution. However, analyses performed on dry powders allowed observing clear evidence of a FRET mechanism. In particular, photoluminescence lifetime measurements showed that FRET efficiency could be effectively increased by both reducing the size of the UCNPs and directly controlling the distribution of the active ions throughout the donor’s volume, i.e., doping them only in the outer shell of a core/shell system. Both strategies resulted at least in a more than doubled FRET efficiency compared to larger core-only UCNPs. Obtained experimental values were compatible with those predicted from geometrical cons...

Enhanced photoluminescence from CuInS2/ZnS quantum dots: Organic superacid passivation

Improvements in CuInS2 photoluminescence is necessary before it can replace cadmium- or lead-based quantum dots. We demonstrate that organic superacid passivation of CuInS2 quantum dots significantly improves photoluminescence, with no significant changes in particle size, composition, or structure. We propose organic superacid passivation reduces surface promoted non-radiative decay.

CuInS2 quantum dot sensitized solar cells with high VOC ≈ 0.9 V achieved using microsphere-nanoparticulate TiO2 composite photoanode

CuInS2 (CIS) based solar cell devices are fabricated by sensitizing TiO2 photoanodes with CIS quantum dots (CIS-QDs). Morphologically different TiO2, viz. Degussa P25 nanoparticles, smooth and fibrous microspheres (SμS and FμS respectively) are used to fabricate photoanodes. CIS-QDs are synthesized using dodecanethiol (DDT), CuI and In(OAc)3 precursors by solvothermal method. DDT surfactant present on the CIS QDs surface is replaced with 3-mercaptopropionic acid in a single phase one step procedure to enable efficient loading of QDs onto photoanode and as linker molecule for charge carrier extraction. The CIS QDs sensitized on SμS and FμS microsphere photoanode layers exhibit a photoconversion efficiency (η) of 3.2% and 1.6%, respectively, in comparison to η ≈ 2.1% for nanoparticulate TiO2 (Degussa P25). Further increase in efficiency is obtained (3.8% for SμS and 2.5% for FμS) when composite photoanode films made of porous microspheres filled with nanoparticulate P25 are used. A maximum efficiency of 3.8% (with JSC ≈ 6.2mA, VOC ≈ 926mV and FF ≈ 66 for cell area ≈ 0.25cm2 and thickness ≈ 20µm) is realized when 4.6nm CIS QDs sensitized on composite photoanode (consisting of 80wt. % SμS and 20wt. % P25) is used. High VOC observed is unprecedented and is possible due to combined effect of SμS+P25 composite photoanode properties such as fewer defects, good connectivity between particles, effective light scattering, minimum recombination, and effective electron transport and size optimized CuInS2 QDs. Electrochemical impedance spectroscopy studies reveal a low interfacial resistance and longer electron life time in SμS+P25 composite photoanodes.

Enhancement of Two-Photon Fluorescence and Low Threshold Amplification of Spontaneous Emission of Zn-processed CuInS2 Quantum Dots

Heavy-metal-free I-III-VI2 quantum dots (QDs) have recently emerged as favorable alternatives to toxic II-VI QDs for optoelectronic and biological applications, but low fluorescence efficiency is a key issue related to the promising nanocrystals. In this work, we demonstrate big enhancement of two-photon fluorescence efficiency and low threshold two-photon pumped amplification of spontaneous emission (ASE) of Zn-processed CuInS2 (CIS) QDs for the first time. The change of two-photon process caused by Zn2+ cation exchange in CIS QDs is systematically investigated. Two-photon ASE in Zn-processed CIS QDs films is achieved with a record of low threshold fluence of 5.7μJ/cm^2. With high two-photon fluorescence quantum yields and low threshold ASE, the Zn-processed CIS QDs could become a promising candidate for two-photon bio-imaging, nonlinear optical and novel QDs laser devices.

Covalently linking CuInS2 quantum dots with a Re catalyst by click reaction for photocatalytic CO2 reduction.

Covalently linking photosensitizers and catalysts in an inorganic-organic hybrid photocatalytic system is beneficial for efficient electron transfer between these components. However, general and straightforward methods to covalently attach molecular catalysts on the surface of inorganic semiconductors are rare. In this work, a classic rhenium bipyridine complex (Re catalyst) has been successfully covalently linked to the low toxicity CuInS2 quantum dots (QDs) by click reaction for photocatalytic CO2 reduction. Covalent bonding between the CuInS2 QDs and the Re catalyst in the QD-Re hybrid system is confirmed by UV-visible absorption spectroscopy, Fourier-transform infrared spectroscopy and energy-dispersive X-ray measurements. Time-correlated single photon counting and ultrafast time-resolved infrared spectroscopy provide evidence for rapid photo-induced electron transfer from the QDs to the Re catalyst. Upon photo-excitation of the QDs, the singly reduced Re catalyst is formed within 300 fs. Notably, the amount of reduced Re in the linked hybrid system is more than that in a sample where the QDs and the Re catalyst are simply mixed, suggesting that the covalent linkage between the CuInS2 QDs and the Re catalyst indeed facilitates electron transfer from the QDs to the Re catalyst. Such an ultrafast electron transfer in the covalently linked CuInS2 QD-Re hybrid system leads to enhanced photocatalytic activity for CO2 reduction, as compared to the conventional mixture of the QDs and the Re catalyst.