Copper Indium Sulfide Research Articles

Incorporation of luminescent semiconductor nanoparticles into liquid crystal matrix

Characterization of size of synthesized semiconductor copper indium sulfide (CuInS2) nanoparticles used for doping liquid crystal E7 is presented. The method of production of uniform dispersions of the nanoparticles in liquid crystals avoiding aggregation of the nanoparticles is discussed. It was possible to prepare doped liquid crystal with almost uniform dispersion of nanoparticles in the cell, which are visible as defects in homogenous liquid crystal phase. Electrorefractive and photo-electrorefractive characterizations of the mixtures have been done with pure E7 sample as a reference and the results are discussed.

Photoelectrochemical Cells Studies with Pulse Electrodeposited CuInS2 Films

Copper Indium Sulphide(CISu) thin films were deposited on conducting glass substrates at different duty cycles in the range of 6 % – 50 %and at a current density of 10 mA cm-2. The precursors were solutions of 0.1 M CuCl2, 0.1 M InCl3 and 0.2 M of sodium thiosulphate. The deposition current density was fixed at 10 mA cm-1. The deposition time was fixed as 60 min in all cases. Thickness of the films measured by gravimetry using a semimicro Mettler balance were observed to be in the range of 500 – 700 nm with an increase of duty cycle from 6% to 50% (sensitivity of the semimicro balance is 10 μg). XRD patterns of CISu films deposited at different duty cycles were polycrystalline with peaks corresponding to the chalcopyrite phase of CISu. Peaks corresponding to CuS were not present. XRD peaks of the chalcopyrite phase, namely, (112), (204 ), (3 1 2). The height of the peak increased with duty cycle and the width of the peaks decreased with increase of duty cycle. The crystallite size determined using Scherrer’s equation, increased from 10 nm to 25 nm with increase of duty cycle. Composition of the films was estimated by recording the EDS spectrum of the films deposited at different duty cycles. It is observed that films deposited at lower duty cycles were copper rich. As the duty cycle increased, the films became stochiometric. For the films deposited at 50 % duty cycle, Cu/In ratio was 1.0. Bandgap values of 1.39 eV, 1.41 ev and 1.51 eV were obtained from Tauc’s plot. The band gaps of most of the as-prepared films correspond to theoretical value of CuInS2 at 1.53 eV. Band gap decreases with increase of duty cycle. These changes are directly related to the phase composition of the CISu films. The room temperature transport parameters were measured by Hall Van der Pauw technique by providing gold ohmic contact. The films exhibit p-type conductivity, which is supported by the EDAX results, since, the non-stochiometry parameter is greater than zero. The magnitude of the resistivity increased from 0.10 ohm cm to 3.67ohm cm as the duty cycle is increased. The resistivity values of this work are lower than the earlier report of 80.5 ohm cm for the films with Cu/In ratio of unity. The values of mobility and carrier density decrease with increase of duty cycle. Mobility is 2.43 cm2V-1s-1 for Cu/In ratio of unity is lower than 4.92 cm2V-1s-1 and carrier density value of 3.998 x 1018 cm-3 for Cu/In ratio of unity in this study is higher than 1.2 x 1016 cm-3 for Cu/In ratio of unity reported earlier. The PEC cells using these films exhibited low photocurrent and photovoltage. In order to increase the photo outpout, the films deposited at 50 % duty cycle were post heated in argon atmosphere at different temperatures in the range of 450 - 550°C for 15 min. Photoelectrodes heat-treated at temperatures greater than this value exhibited lower open circuit voltage and short circuit current due to the reduction in thickness of the films as well as the slight change in stoichiometry. For a film deposited at 50 % duty cycle, an open circuit voltage of 0.55 V and a short circuit current density of 12.0 mA cm-2 at 60 mW cm-2 illumination. The photooutput is higher than earlier report. A plot of lnJsc vs Voc yielded a straight line. Extrapolation of the line to the y-axis yields a J0 value of 5.1 x 10-7 A cm-2, the ideality factor (n) was calculated from the slope of the straight line and it was found to be 1.85. Photoetching was done by shorting the photoelectrodes and the graphite counter electrode under an illumination of 100 mW cm-2 in 1 : 100 HNO3 for different durations in the range 0 – 100s. Both photocurrent and photovoltage are found to increase up to 80s photoetch, beyond which they begin to decrease. This is illustrated in Fig.4.13 for the CIS photoelectrode deposited at 50 % duty cycle. The decrease of the photocurrent and photovoltage after 80s photoetch is attributable to separation of grain boundaries due to prolonged photoetching. The power output characteristics after 80s photoetching indicates a Voc of 0.625V, Jsc of 16.0 mA cm-2, ff of 0.71 and h of 11.83 %, for 60 mW cm-2 illumination.

Preparation of Copper Indium Sulfide Film by Electro-Deposition Method

Abstract Copper indium sulfide (CuInS 2 , CIS 2 ) film was prepared by an electro-deposition method. Uv-vis spectrophotometer test result shows that the band gap of the electroplated CIS 2 film is 1.5 eV. X-ray photoelectron spectroscopy (XPS) analysis reveals that the Cu, In and S signals corresponded to valence state (+1, +3 and −2) of three elements in CIS 2 film, respectively. The photoelectrical properties of the CIS 2 film were characterized by linear sweep voltammetry measurements under the dark and illumination. The I – V characteristic is linear under the dark and illumination, and the slope gap is 0.6×10 −3 . We also simulated the band gap (1.5 eV) of the CIS 2 film with chalcopyrite structure prepared by electroplating experiment using DMol3 and CASTEP modules, respectively. The molecular structure model of electroplated copper indium sulfide film has been established, and the X-ray diffraction simulative spectrum has been obtained by Materials Studio, which has good agreement with the experiment result.

Electrocatalytic Reduction of Carbon Dioxide using Sol-gel Processed Copper Indium Sulfide (CIS) Immobilized on ITO-Coated Glass Electrode

Sol-gel processed copper indium sulfide (CIS) films have been processed on glass and transparent indium doped tin oxide (ITO)-coated glass electrodes by a straightforward layer by layer spin coating route yielding excellent film qualities with subsequent thermal annealing. Resulting films were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), and UV-vis spectroscopy. We apply these films in an electrochemical cell as a working electrode and take a view on the reduction of carbon dioxide (CO2) to its energy richer carbon monoxide (CO) in acetonitrile solution containing 0.1 M (C4H9)4NPF6 supporting electrolyte saturated with CO2. CIS films exhibit pronounced electrochemical and photoelectrochemical activities. Concomitantly, we quantify the generation of CO, which starts to evolve at a threshold potential of −0.60 V vs normal hydrogen electrode (NHE). The calculated faradaic efficiency of the electrochemical reduction of CO2 into CO exceeds 20 (±1) % in an optimized thin-film structure.

Microwave-Assisted Solution–Liquid–Solid Synthesis of Single-Crystal Copper Indium Sulfide Nanowires

Chalcopyrite copper indium sulfide (CuInS2) is an important semiconductor with a bandgap optimal for terrestrial solar energy conversion. Building photovoltaic and microelectronic devices using one-dimensional CuInS2 nanowires can offer directional conduits for rapid and undisrupted charge transport. Currently, single-crystal CuInS2 nanowires can be prepared only using vapor-based methods. Here, we report, for the first time, the synthesis of single-crystal CuInS2 nanowires using a microwave-assisted solution–liquid–solid (MASLS) method. We show that CuInS2 nanowires with diameters of less than 10 nm can be prepared at a rapid rate of 33 nm s–1 to more than 10 μm long in less than 10 min, producing a high mass yield of 31%. We further show that the nanowires are free of structural defects and have a near-stoichiometric composition. The success of MASLS in preparing high-quality tertiary nanowires is explained by a eutectic growth mechanism involving an overheated alloy catalyst.

Annealing-Induced Effects on the Chemical Structure of the In2S3/CuIn(S,Se)2 Thin-Film Solar Cell Interface

We have investigated the impact of heat treatments on the chemical structure of the In2S3/CuIn(S,Se)2 thin-film solar cell interface using X-ray photoelectron and soft X-ray emission spectroscopy. As-grown, we find the formation of a sulfur-poor (indium-rich) In2S3 surface, an abrupt interface, and sulfur atoms in both In2S3 and CuIn(S,Se)2 chemical environments (as expected for an abrupt interface and a thin overlayer). After a heat treatment at 200 °C to simulate subsequent process steps, a strong copper and sodium diffusion into the In2S3 layer is observed. This diffusion extends throughout the layer, indicating the formation of a copper–indium–sulfide phase.

Non-toxic and environmentally friendly route for preparation of copper indium sulfide based thin film solar cells

In this study, copper based thin film solar cells with substrate structure have been built via spray pyrolysis method. Toxic material usage was avoided during the material deposition and the post-treatment steps. Novel device configuration of Mo/CuInS2/In2S3/ZnO/AZO–Ag–AZO was studied as a function of the In2S3 buffer layer thickness. In order to utilize the zinc oxide (ZnO) and aluminum doped zinc oxide (AZO) transparent conductive layers, deposited by physical vapor deposition (PVD), on top of the spray pyrolyzed thin films, the RF power was lowered to 30W. Although this minimized the unwanted penetration of the highly energetic particles, created during PVD process, sheet resistivity of the AZO films increased enormously. Hence very thin silver layer has been deposited between two AZO films. This resulted the decrease in the sheet resistivity more than 106 times. Electrical measurements under illumination revealed that short circuit current density (Jsc), open circuit voltage (Voc), fill factor (FF) and efficiency (η) of the Mo/CuInS2/In2S3/ZnO/AZO–Ag–AZO type solar cells increased with increasing the thickness of the In2S3 layer. The maximum Jsc of 9.20mA/cm2, Voc of 0.43V, FF of 0.44 have been observed for the 0.94μm-thick In2S3 layer. Extraordinarily thick buffer layer provided better diffusion barrier between the absorber and the TCO layers and also resulted better photosensitivity. These could be the key factors to produce substrate configuration of the spray pyrolyzed thin film solar cells.

A high efficient photoluminescence Zn–Cu–In–S/ZnS quantum dots with long lifetime

Highly Cu-rich copper indium sulfide (CuInS2, CIS) quantum dots were synthesized utilizing copper chloride (CuCl) and indium acetate (In(Ac)3) as metal cation precursors, combined with n-dodecanethiol (DDT) as a coordinating sulfur source and solvent. With excess of In(Ac)3, i.e. with Cu/In ratios of 1/4, together with Zn2+ ions post-treatment, a relatively high photoluminescence quantum yield (QY) of ∼73% with long average lifetime of ∼359ns has been obtained, which is proposed to be attributed to the Cu-rich defect states in the CIS nanocrystals (NCs) nuclei. Meanwhile, the formation of In-rich CIS–ZnS alloy, i.e. Zn–Cu–In–S (ZCIS) with high density of Cu vacancies, combined with the surface passivation of ZnS overlay resulted in a high QY. Finally, the formation mechanism of the ZCIS/ZnS with Cu-rich nuclei has been proposed.

Synthesis of CuInS2 quantum dots using polyetheramine as solvent.

This paper presents a facile solvothermal method of synthesizing copper indium sulfide (CuInS2) quantum dots (QDs) via a non-coordinated system using polyetheramine as a solvent. The structural and optical properties of the resulting CuInS2 QDs were investigated using composition analysis, absorption spectroscopy, and emission spectroscopy. We employed molar ratios of I, III, and VI group elements to control the structure of CuInS2 QDs. An excess of group VI elements facilitated precipitation, whereas an excess of group I elements resulted in CuInS2 QDs with high photoluminescence quantum yield. The emission wavelength and photoluminescence quantum yield could also be modulated by controlling the composition ratio of Cu and In in the injection stock solution. An increase in the portion of S shifted the emission wavelength of the QDs to a shorter wavelength and increased the photoluminescence quantum yield. Our results demonstrate that the band gap of the CuInS2 QDs is tunable with size as well as the composition of the reactant. The photoluminescence quantum yield of the CuInS2 QDs ranged between 0.7% and 8.8% at 250°C. We also determined some important physical parameters such as the band gaps and energy levels of this system, which are crucial for the application of CuInS2 nanocrystals.

Synthesis of Copper Indium Sulfide Nanoparticles Via Microwave Approach and Investigation of Their Behavior in Solar Cells

This study focuses on the preparation and characterization of single phase CuInS2 nanoparticles with [diaquabis(salisylate)copper(II)], [Cu(Hsal)2(H2O)2] as precursor via microwave technique. Several effects on product morphology have been investigated, such as sulfur sources, solvent, power, and time of microwave. The products were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, UV-visible spectroscopy, Fourier transform infrared spectroscopy, and photoluminescence spectroscopy. Thin films CuInS2 were prepared by doctor's blade method and then studied via I-V characterization.

Photoluminescence of indium-rich copper indium sulfide quantum dots

The enhanced photoluminescence (PL) for In-rich copper indium sulfide quantum dots (CIS QDs) was observed. The conduction electron-Cu vacancy recombination and the donor–acceptor pair (DAP) defect recombination were considered to exist in CIS QDs at the same time. The temperature-dependent PL study showed that the emission of these QDs might be mainly originated from the recombination between electrons in the quantized conduction band and holes in the copper vacancy acceptor when x was 0.500 (CuxIn1−xS). However, the temperature coefficient of PL peak position decreased when x was 0.237. That meant the DAP recombination increased in the In-rich CIS QDs.

Photoinduced Carrier Dynamics of Nearly Stoichiometric Oleylamine-Protected Copper Indium Sulfide Nanoparticles and Nanodisks

Copper indium sulfide (CuInS2) nanocrystals (NCs) are nontoxic and cost-effective, making them attractive for use in highly efficient solar cells. However, direct observations of the photoinduced carrier dynamics of CuInS2 NCs to examine the relationship between carrier dynamics and structural parameters with the aim of optimizing NC properties for specific applications are limited. Here, we synthesized nearly stoichiometric oleylamine-protected CuInS2 NCs using two convenient one-pot methods to produce CuInS2 nanoparticles and nanodisks. Transient absorption measurements using femtosecond laser flash photolysis revealed that the use of oleylamine as a protecting ligand leads to the formation of vacancy-doped NCs. The rapid decay of the photogenerated excitons in the oleylamine-protected NCs was not sensitive to the crystal structure or shape of NCs, and could be explained by defect trapping and energy transfer to the hole-based localized surface plasmon resonance in the oleylamine-protected NCs. Our resu...

The effects of post-processing on the surface and the optical properties of copper indium sulfide quantum dots

In the current contribution we report on investigations regarding the surface of CuInS2 quantum dots and on different strategies to control the amount of surface ligands in a post-processing step. In particular, the reactivity of the organic components, that is, 1-dodecanthiol and 1-octadecene as ligand and solvent, respectively, during nanocrystal formation was studied. A new method to remove residuals from the reaction mixture and to detach excess organics from the surface of the nanocrystals is reported. Our new method, which is based on the utilization of acids, is compared with standard purification procedures by means of thermogravimetric analysis (TGA) with particular focus on its efficiency to remove organics. As a complement, the surface chemistry is analyzed by nuclear magnetic resonance spectroscopy (NMR) to shed light on the nature of the organic components still present after purification. Further analysis of the product by inductively coupled plasma optical emission spectroscopy (ICP-OES) is performed to verify the influence of the new purification method on surface composition and properties. Moreover, steady state and time resolved spectroscopies give insights into excitonic behavior as well as recombination processes. Finally, the new method is optimized for the purification of CuInS2–ZnS nanocrystals, which show enhanced optical properties.

Deposition of ultra thin CuInS2 absorber layers by ALD for thin film solar cells at low temperature (down to 150 °C)

Two new processes for the atomic layer deposition of copper indium sulfide (CuInS2) based on the use of two different sets of precursors are reported. Metal chloride precursors (CuCl, InCl3) in combination with H2S imply relatively high deposition temperature (Tdep = 380 °C), and due to exchange reactions, CuInS2 stoechiometry was only achieved by depositing In2S3 layers on a CuxS film. However, the use of acac- metal precursors (Cu(acac)2, In(acac)3) allows the direct deposition of CuInS2 at temperature as low as 150 °C, involving in situ copper-reduction, exchange reaction and diffusion processes. The morphology, crystallographic structure, chemical composition and optical band gap of thin films were investigated using scanning electronic microscope, x-ray diffraction under grazing incidence conditions, x-ray fluorescence, energy dispersive spectrometry, secondary ion mass spectrometry, x-ray photoelectron spectroscopy and UV–vis spectroscopy. Films were implemented as ultra-thin absorbers in a typical CIS-solar cell architecture and allowed conversion efficiencies up to 2.8%.

From Binary Cu2S to ternary Cu-In-S and quaternary Cu-In-Zn-S nanocrystals with tunable composition via partial cation exchange.

We present an approach for the synthesis of ternary copper indium sulfide (CIS) and quaternary copper indium zinc sulfide (CIZS) nanocrystals (NCs) by means of partial cation exchange with In(3+) and Zn(2+). The approach consists of a sequential three-step synthesis: first, binary Cu2S NCs were synthesized, followed by the homogeneous incorporation of In(3+) by an in situ partial cation-exchange reaction, leading to CIS NCs. In the last step, a second partial exchange was performed where Zn(2+) partially replaced the Cu(+) and In(3+) cations at the surface, creating a ZnS-rich shell with the preservation of the size and shape. By careful tuning reaction parameters (growth and exchange times as well as the initial Cu(+):In(3+):Zn(2+) ratios), control over both the size and composition was achieved. This led to a broad tuning of photoluminescence of the final CIZS NCs, ranging from 880 to 1030 nm without altering the NCs size. Cytotoxicity tests confirmed the biocompatibility of the synthesized CIZS NCs, which opens up opportunities for their application as near-infrared fluorescent markers in the biomedical field.

Role of copper sulfide seeds in the growth process of CuInS2 nanorods and networks.

CuInS2 nanorods and networks are interesting candidates for applications requiring efficient charge transport, such as solar energy conversion, because of the increased electrical conductivity in elongated or interconnected nanocrystals, compared to isolated, quasi-spherical ones. However, little is known about the growth mechanisms involved in the formation of this kind of nanostructures, yet. Here, CuInS2 nanorods and networks were synthesized through a facile low-cost and phosphine-free method. Copper and indium sources were added together in the presence of oleylamine and oleic acid. Changing the amount of oleic acid present in the reaction solution influenced the reactivity of the monomers, and consequently, the size of copper sulfide seeds formed in situ after the injection of tert-dodecanethiol, serving as the source of sulfur. Two different growth mechanisms of CuInS2 nanorods were observed, depending on the size of the copper sulfide seeds. Larger seeds (8 nm), which were generated with relatively small amounts of oleic acid, resulted in the formation of hybrid copper sulfide-copper indium disulfide nanocrystals as intermediates in the growth process of the nanorods, while smaller seeds (4 nm) obtained with relatively large amounts of oleic acid were gradually converted to copper indium sulfide nanorods. At longer reaction times, these nanorods formed network structures. The reaction between oleylamine and oleic acid at high temperature turned out to be the crucial factor to induce the attachment of nanorods to multipods and networks.

Photoactive nanocrystals by low-temperature welding of copper sulfide nanoparticles and indium sulfide nanosheets.

We successfully utilize the concept of coalescence and room-temperature sintering to prepare morphologically different nanoparticles. n-Type chalcogenide (CuIn5 S8 ) nanocrystals are synthesized at room temperature by simple mixing of oppositely charged precursor nanoparticles. The coalescence of polycation-coated CuS nanoparticles and negatively charged In2 S3 nanoplates is driven by close contact of the particles due to electrostatic interactions. Analysis by X-ray diffraction, transmission electron microscopy (TEM) imaging, and Raman spectroscopy confirms the formation of single-phase CuIn5 S8 without traceable secondary phase. In a photovoltaic device, the use of the coalesced particles yields a power conversion efficiency of 1.8%.

Sol–gel derived In2S3 buffer layers for inverted organic photovoltaic cells

In2S3 – a wide-gap semiconductor – has been implemented in organic photovoltaics using an all-solution based sol–gel route. Typically, indium sulfide is deployed as a buffer layer in copper–indium sulfide (CIS) photovoltaic systems as electron-selective contact on the bottom electrode. We transferred this idea to organic, solution-processed photovoltaics, exploring its potential in an inverted hybrid device structure. The optical and morphological properties of the films were investigated by UV–Vis transmittance spectroscopy and scanning electron microscopy. The optical studies showed that the In2S3 films exhibit a band gap of ∼2.25eV. The effect of In2S3 film thickness on conversion efficiency of the device was also investigated. The device with the 158±5nm of In2S3 film thickness provides the best performance with an average short-circuit current density (Jsc) of approximately 7.96±0.12mA/cm2, open-circuit voltage (Voc) of 0.609±0.007 V, fill factor (FF) of 0.49±0.014, and power conversion efficiency of 3.04±0.14%.

High color rendering index white light emitting diodes fabricated from a combination of carbon dots and zinc copper indium sulfide quantum dots

In a line with most recent trends in developing non-toxic fluorescent nanomaterials, we combined blue emissive carbon dots with green and red emissive zinc copper indium sulfide (ZCIS) core/shell quantum dots (QDs) to achieve white light-emitting diodes (WLEDs) with a high color rendering index of 93. This indicates that ZCIS QDs, with their broad emission bands, can be employed to effectively make up the emission of carbon dots in the yellow and red regions to produce WLEDs in the wide region of color temperature by tuning the volume ratio of these constituting luminophores. Their electroluminescence characteristics including color rendering index, Commission Internationale de l'Eclairage (CIE) color coordinates, and color temperatures were evaluated as a function of forward current. The CIE-1931 chromaticity coordinates of the as-prepared WLEDs, exhibiting good stability, were slightly shifted from (0.321, 0.312) at 10 mA to (0.351, 0.322) at 30 mA, which was mainly caused by the different thermal quenching coefficients of carbon dots and ZCIS QDs.

Influence of excitation frequency on structural and electrical properties of spray pyrolyzed CuInS2 thin films

This paper reports the cost effective deposition of the copper indium sulfide (CuInS2) thin films under atmospheric conditions via ultrasonic spray pyrolysis. Structural and electrical properties of these films have been tailored by controlling the nozzle excitation frequency and the solution loading. Smoother films have been obtained via 120kHz excitation frequency compare to the 48kHz. Band gap energy of the films has also been tailored via excitation frequency. UV–vis–NIR analysis revealed that films deposited at 48kHz excitation frequency had lower band gap energies. Although, both excitation frequencies resulted chalcopyrite structure, crystallinity of the CuInS2 films was better for 120kHz. On the other hand, better optical absorption in visible and near infrared region was observed at 48kHz. Moreover, room temperature electrical conductivity of the samples deposited at 48kHz excitation frequency was higher than that of samples deposited at 120kHz. Temperature dependent electrical conductivity data showed that variable range hopping mechanism can be used to explain the conduction of spray pyrolyzed CuInS2 thin films. Electrical mobility as high as 48cm2/Vs has been observed for the sample deposited from 0.51ml/cm2 loading at 48kHz excitation frequency. This value is very close to the mobility of vacuum deposited thin films like amorphous silicon, which is one of the most commonly used semiconductor in electronic and energy applications.