CuInS2 Quantum Dots Research Articles

Electronic transition responsible for size-dependent photoluminescence of colloidal CuInS2quantum dots

Colloidal CuInS2 quantum dots with an average size of 2.9–4.1 nm were synthesized by the one-pot heating of an organometallic solution. The size-dependent optical gaps and photoluminescence (PL) emission energies were analyzed based on the finite-depth well effective mass approximation. The PL emission was attributed to the recombination of electrons in the donor level and holes in the quantized hole state. Indium atom defects at copper sites or sulfur vacancies were proposed to be the defects acting as donors at ∼0.1 eV below the conduction band.

High-efficiency "green" quantum dot solar cells.

Semiconductor quantum dots (QDs) are extremely interesting materials for the development of photovoltaic devices, but currently the present the drawback is that the most efficient devices have been prepared with toxic heavy metals of Cd or Pb. Solar cells based on "green" QDs--totally free of Cd or Pb--present a modest efficiency of 2.52%. Herein we achieve effective surface passivation of the ternary CuInS2 (CIS) QDs that provides high photovoltaic quality core/shell CIS/ZnS (CIS-Z) QDs, leading to the development of high-efficiency green QD solar cells that surpass the performance of those based on the toxic cadmium and lead chalcogenides QDs. Using wide absorption range QDs, CIS-Z-based quantum dot sensitized solar cell (QDSC) configuration with high QD loading and with the benefit of the recombination reduction with type-I core/shell structure, we boost the power conversion efficiency of Cd- and Pb-free QDSC to a record of 7.04% (with certified efficiency of 6.66%) under AM 1.5G one sun irradiation. This efficiency is the best performance to date for QDSCs and also demonstrates that it is possible to obtain comparable or even better photovoltaic performance from green CIS QDs to the toxic cadmium and lead chalcogenides QDs.

Investigation of the Photophysical and Electrical Characteristics of CuInS2 QDs/SWCNT Hybrid Nanostructure

A novel photoactive hybrid nanostructure based on zero-dimensional (0-D) light-harvesting components of CuInS2 quantum dots (QDs) and one-dimensional (1-D) transporting channel of single-wall carbon nanotube (SWCNT) was synthesized by hydrophobic interaction between alkyl chain of dodecanethiol molecule (QDs surface) and octadecylamine (CNT surface). Photophysical and electrical characterizations suggest that an efficient electron transfer from photoexcited CIS QDs to SWCNT takes place. Furthermore, size-dependent optical study shows that faster electron transfer takes place from CIS to SWCNT for small-size QDs compared to large-size quantum dots. The rate constant for electron transfer from photoexcited CIS to SWCNT increased from 1.9 × 106 to 3.5 × 106 s–1 with decrease in the size of CIS QDs from 5.0 to 3.5 nm.

A near-infrared turn-on fluorescent nanosensor for zinc(II) based on CuInS2 quantum dots modified with 8-aminoquinoline

We describe a novel near-infrared (NIR) “turn-on” fluorescent nanosensor for highly sensitive and selective detection of Zn(II) ion. It is based on the use of the fluorescent probe 8-aminoquinoline conjugate to CuInS2 quantum dots. Water-soluble CuInS2 QDs capped by mercaptopropionic acid (MPA) were synthesized in aqueous solution via a hydrothermal method, and the carboxy groups on the surface of the capped QDs were then covalently linked to the amino groups of the probe 8-aminoquinoline to form the conjugate acting as a nanosensor. The fluorescence of the modified QDs is almost completely quenched via a hole-transfer mechanism. If, however, Zn(II) is added, the lone pair electrons of the nitrogen atom of 8-aminoquinoline become involved into the mechanism of binding Zn(II), and hole-transfer quenching is suppressed which results in turn-on fluorescence. The nanoprobe enables Zn(II) to be determined by measurement of the increase in fluorescence intensity. Under optimized experimental conditions, the nanosensor displays a wide and fairly linear response in the 0.005 to 1 mM concentration range, with a 4.5 μM detection limit. The nanosensor reported here was successfully employed to the detection of Zn(II) in spiked tap water samples.

Ultrafast charge dynamics in CuInS2 nanocrystal quantum dots

Colloidal CuInS2 quantum dots have been synthesised and characterised using absorption and photoluminescence spectroscopy, X-ray diffraction, inductive-coupled plasma atomic emission spectroscopy and thermogravimetric analysis. The ultrafast charge dynamics of these dots have been studied using transient absorption spectroscopy. Cooling of hot photo-generated carriers to the band edge occurred within 3–5ps. Significant de-population of the band-edge was found to occur on a sub-nanosecond time-scale, and was attributed to hole-trapping.

Enhancement of memory margins for stable organic bistable devices based on graphene-oxide layers due to embedded CuInS2 quantum dots

Current–voltage (I–V) curves for Al/CuInS2 (CIS) quantum dots (QDs) embedded in graphene-oxide layer/indium-tin-oxide devices at 300K showed a current bistability with a maximum high conductivity (ON)/low conductivity (OFF) ratio of 1×104, which was 100 times larger than the ON/OFF ratio of the device without CIS QDs. I–V curves and write-read-erase-read voltage cycles demonstrated the rewritable nonvolatile memory properties of the organic bistable devices (OBDs) with ON and OFF current states at the same voltage. The retention time was above 1×105s, indicative of the memory stability of the OBDs. I–V curve at lower voltages up to 0.05V was attributed to the thermionic emission mechanism, and the curve in the applied voltage range from 0.06 to 0.17V was related to an ohmic mechanism. The I–V characteristics in the applied voltage above 0.18V dominantly followed the space-charge-limited-current behaviors.

Size-dependent polymer/CuInS2 solar cells with tunable synthesis of CuInS2 quantum dots

This paper reports the size-dependent performance in polymer/CuInS2 solar cells with tunable synthesis of chalcopyrite CuInS2 quantum dots (QDs) by the solvothermal method. The CuInS2 QDs of 3.2–5.4nm in size are fine tuned by the reaction time in the solvothermal process with the slow supply of In3+ ions during the crystallization, and the band gaps increased with QDs sizes decreasing according to the results from the characterization of sizes, morphologies, component elements, valence states and band gaps of CuInS2 QDs. We fabricated MEH-PPV/CuInS2 solar cells, and the photoactive layer of device displayed size-dependent light-harvesting, charge separation and transport ability. Moreover, the solar cells exhibit size-dependent short circuit current (Jsc) and open circuit voltage (Voc), with higher performance in both Jsc and Voc for smaller CuInS2 QDs, resulting in the maximum power conversion efficiency of ca. 0.12% under the monochromic illumination at 470nm; CuInS2 QDs actually serve as an effective electron acceptor material for the MEH-PPV/CuInS2 solar cells with the wide spectral response extending from 300 to 900nm.

Influence of crystal phase for CuInS2 on device performance of polymer–CuInS2/oxide nanoarrays solar cells

The paper demonstrates the influence of crystal phase for CuInS2 on device performance of MEH-PPV-CuInS2/oxide nanoarrays hybrid polymer-based solar cells. CuInS2 quantum dots with wurtzite and chalcopyrite crystallographic phases are incorporated into pristine polymer layer as light-harvesting hybrids, while ZnO nanoarrays (ZnO-NA) and TiO2 nanoarrays (TiO2-NA) are used as electron acceptor. Results show that devices with wurtzite CuInS2 quantum dots (WCIS-QDs) exhibited higher photovoltaic performance in MEH-PPV-CuInS2/ZnO-NA solar cells, while devices with chalcopyrite CuInS2 quantum dots (CCIS-QDs) exhibited higher performance in MEH-PPV-CuInS2/TiO2-NA solar cells. It is concluded that the devices based on metal oxide and CuInS2 that belong to the same crystal system contribute to the increased device performance, which possibly results from the more effective energy transfer and transport between metal oxide and CuInS2 with the same crystal system.

Study of relaxation dynamics of photogenerated excitons in CuInS2 quantum dots

Abstract

A novel aptamer functionalized CuInS2 quantum dots probe for daunorubicin sensing and near infrared imaging of prostate cancer cells

In this paper, a novel daunorubicin (DNR)-loaded MUC1 aptamer-near infrared (NIR) CuInS2 quantum dot (DNR–MUC1–QDs) conjugates were developed, which can be used as a targeted cancer imaging and sensing system. After the NIR CuInS2 QDs conjugated with the MUC1 aptamer–(CGA)7, DNR can intercalate into the double-stranded CG sequence of the MUC1–QDs. The incorporation of multiple CG sequences within the stem of the aptamers may further increase the loading efficiency of DNR on these conjugates. DNR–MUC1–QDs can be used to target prostate cancer cells. We evaluated the capacity of MUC1–CuInS2 QDs for delivering DNR to cancer cells in vitro, and its binding affinity to MUC1-positive and MUC1-negative cells. This novel aptamer functionalized QDs bio-nano-system can not only deliver DNR to the targeted prostate cancer cells, but also can sense DNR by the change of photoluminescence intensity of CuInS2 QDs, which concurrently images the cancer cells. The quenched fluorescence intensity of MUC1–QDs was proportional to the concentration of DNR in the concentration ranges of 33–88nmolL−1. The detection limit (LOD) for DNR was 19nmolL−1. We demonstrate the specificity and sensitivity of this DNR–MUC1–QDs probe as a cancer cell imaging, therapy and sensing system in vitro.

Fabrication of the protonated pentatitanate nanobelts sensitized with CuInS2 quantum dots for photovoltaic applications

Abstract Titanate nanomaterials are considered to be the desirable materials for solar cells application because of their special optical absorption properties. In the present paper, protonated pentatitanate nanobelts prepared by hydrothermal method are used as photoanodes by screen-printing method. While CuInS 2 quantum dots with the particle size of 3.5 nm are synthesized by solvothermal method and uniformly linked on the surface of the protonated pentatitanate nanobelt films by 3-Mercaptopropionic acid, which serves as the sensitizers in sensitized solar cells. The sensitization content of the quantum dots on the photoanode is determined by the number of preparative chemical linking cycles. The optical absorption of such sensitized pentatitanate nanobelt films enhances under the full solar spectrum, following with a red-shift of the absorption peak from 308 nm to 325 nm. Under AM 1.5 illumination, the best photovoltaic conversion efficiency of these structures using a sulfide/polysulfide redox electrolyte is about 1.05% following 8 preparative chemical linking cycles, which is better than that of TiO 2 nanocrystalline photoanodes. This result suggests that these photoanodes may have the significant research prospects and potential application in solar cells.

Ultrafast carrier dynamics in CuInS2 quantum dots

The ultrafast carrier dynamics in CuInS2 (CIS) quantum dots (QDs) was studied by means of femtosecond transient absorption (TA) spectroscopy. The size-dependent 1S transition energy determined from bleaching spectra is in agreement with that calculated on the finite-depth-well model in the effective mass approximation. The TA bleaching comes from filling of electron quantized levels, allowing us to know the dynamics of the 1S electron in CIS QDs. The sub-100-ps electron trapping at surface defects in bare QDs accelerates with decreasing QD size, while is effectively suppressed in well-passivated CIS/ZnS core/shell QDs.

Controllable synthesis of ultrasmall CuInSe2 quantum dots for photovoltaic application

Ultrasmall CuInSe2 quantum dots were synthesized by a facile solvothermal method and used as a sensitizer in CdS/CuInSe2 quantum dot solar cells to improve the photovoltaic performance.

Near-infrared fluorescence probe for the determination of alkaline phosphatase

Water-soluble CuInS2 quantum dots (QDs) were directly synthesized in an aqueous solution with mercaptopropionic acid (MPA) as stablizers, and were functionalized using tryptophan molecules to form tryptophan-functionalized CuInS2 QDs (W-CuInS2 QDs) that had a strong fluorescence emission around 689nm. The fluorescence of W-CuInS2 QDs could be quenched by Cu2+ and then the addition of pyrophosphate (PPi) could effectively turn on the quenched fluorescence due to the strong interaction between Cu2+ and PPi. The alkaline phosphatase (ALP) could catalyze the hydrolysis of PPi that would disassemble the complex of PPi–Cu2+–PPi. Therefore, the recovered fluorescence could be quenched again by the addition of ALP. In this paper, we developed a novel near-infrared fluorescence probe for the simple and convenient assay of ALP.

Photoelectrochemical behavior of TiO2 nanorod arrays decorated with CuInS2 quantum dots

One-dimensional single crystalline TiO2 nanorod arrays with different lengths were prepared by controlling the hydrothermal cycles, which were successfully sensitized with CuInS2 quantum dots by assembly linking cycles, and their optical absorption properties and photoelectrochemical properties were investigated. 6μm-TiO2 nanorod electrodes with the CuInS2 quantum dots sensitization of three linking cycles had the best photoelectrochemical properties and short-circuit current density, such as the short-circuit current density are 27.3 times higher than that of pure 6μm-TiO2 nanorod electrodes. The reason may be attributed to the suitable internal surface area of TiO2 nanorod, with the increasing of the adsorption content of CuInS2 quantum dots to generate much more photo-induce electrons. Moreover, it will also enhance the interface connection between TiO2 nanorod and FTO conducting substrate, which favors to reduce the recombination of photo-induced electron–hole pairs.

Ternary MEH-PPV-CuInS2/ZnO solar cells with tunable CuInS2 content

The paper reports novel ternary MEH-PPV-CuInS2/ZnO solar cells fabricated by incorporating CuInS2 quantum dots (QDs) into pristine MEH-PPV as light-harvester and vertically aligned ZnO nanorod array as electron acceptor. Results show that, MEH-PPV-CuInS2/ZnO solar cells exhibit increased photovoltaic performance compared to MEH-PPV/ZnO devices and the performance dependent on the weight ratio (R) between CuInS2 and MEH-PPV, resulting in a peak power conversion efficiency of 2.48% for R=0.6 at 15.85mW/cm2 monochromatic illumination. It is revealed that the increased Jsc is due to the improved light-harvesting, additional MEH-PPV/CuInS2 interfaces for exciton dissociation, and the formation of CuInS2 channels for effective charge transport, while the increased Voc and the decreased charge recombination are attributed to the modification of ZnO surface by CuInS2 QDs which reduces the surface defect concentration of ZnO. However, the decreased Jsc, Voc at too high R value are attributed to the serious aggregations of CuInS2 QDs resulting in the inorganic nanocrystals not well dispersed in organic matrix.

A novel fluorescent nanosensor for detection of heparin and heparinase based on CuInS2 quantum dots

In this work, a novel fluorescence “turn off–on” nanosensor for the determination of heparin and heparinase based on CuInS2 quantum dots (QDs) was established. CuInS2 QDs (modified by l-cysteine) featuring amino groups were directly prepared in aqueous solution via a hydrothermal synthesis method. The amino groups on the surface of CuInS2 QDs can interact with sulfate and carboxylate groups in heparin via electrostatic interactions and hydrogen bonding, which led the fluorescence of CuInS2 QDs to “turn-off”. However, the heparin could be hydrolyzed into small fragments in the presence of heparinase, which resulted in the fluorescence of CuInS2 QDs being recovered. Therefore, the addition of heparinase to the heparin/CuInS2 QDs system activated the fluorescence of CuInS2 QDs to “turn-on” state. Thus, the determination of heparin and heparinase could be achieved by monitoring the fluorescence “turn off–on”. Under the optimum conditions, there was a good linear relationship between I/I0 (I and I0 were the fluorescence intensity of CuInS2 QDs in the presence and absence of heparin, respectively) and heparin concentration in the range of 0.05–15μmolL−1 with the detection limit of 12.46nmolL−1. The linear detection for heparinase was in the range of 0.2–5μgmL−1 with the detection limit of 0.07μgmL−1. The proposed nanosensor was employed for the detection of heparin in fetal bovine serum samples with satisfactory results.

CuInS2 quantum dots/poly(l-glutamic acid)–drug conjugates for drug delivery and cell imaging

A new anticancer drug delivery system was developed based on the electrostatic complex of positively charged CuInS2 quantum dots (QDs) and negatively charged poly(l-glutamic acid) (PGA) conjugated with the model anticancer drug doxorubicin (DOX). Water-soluble near-infrared CuInS2 QDs capped with l-cysteine were directly synthesized by a hydrothermal method. DOX can quench the photoluminescence of CuInS2 QDs in QDs/PGA-DOX nanoparticles through a photoinduced electron transfer process, thus CuInS2 QDs are in the fluorescence "turn-off" state. After the QDs/PGA-DOX nanoparticles are exposed to carboxypeptidase or are taken up by cancer cells, PGA is hydrolysed to release DOX, inducing activation of the CuInS2 QDs fluorescence to the "turn-on" state. The QDs/PGA-DOX nanoparticles can deliver DOX to targeted cancer cells and monitor the DOX release based on the fluorescence "turn-on" signal of CuInS2 QDs, and this could be simultaneously used for the imaging of cancer cells. The multifunctional QDs/PGA-DOX nanoparticles have great potential in terms of their clinical application for cancer therapy.

Albumin coated CuInS2 quantum dots as a near-infrared fluorescent probe for NADH, and their application to an assay for pyruvate

Water-soluble CuInS2 quantum dots (QDs) stabilized with 3-mercaptopropionic acid were synthesized in aqueous solution and then coated with bovine serum albumin. The resulting particles display fluorescence with a peak at 680 nm that is effectively quenched by 1, 4-dihydro-nicotinamide adenine dinucleotide (NADH), but not by 1, 4-nicotinamide adenine dinucleotide (NAD+). The enzyme lactate dehydrogenase catalyzes the reduction of pyruvate and dehydrogenation of lactic acid using NAD+ or NADH as a cosubstrate. The new QDs were applied to monitor the course of lactate dehydrogenase-catalyzed reaction of pyruvate by detecting NADH via its quenching effect. This resulted in a convenient and selective detection scheme for pyruvate. The detection limit is as low as 25 nM.

ZnSe passivation layer for the efficiency enhancement of CuInS2 quantum dots sensitized solar cells

The effect of ZnSe passivation layer is investigated in the CuInS2 quantum dot sensitized solar cells, which is used to improve the photovoltaic performance. The CuInS2 quantum dot sensitized TiO2 photo-anodes are prepared by assembly linking technique, and then deposited by the ZnSe passivation layer using the successive ionic layer absorption and reaction technique. The optical absorption edge and photoluminescence peak have slightly red-shifted after the passivation layer coating. Under solar light illumination, the ZnSe passivation layer based CuInS2 quantum dot sensitized solar cells have the higher photovoltaic efficiency of 0.95% and incident photon conversion efficiency response than that of pure CuInS2 based solar cells and ZnS passivation layer based solar cells, as the electron injection rate becomes faster after coating with ZnSe passivation layer.