Chalcopyrite CuInS2 Research Articles

Optical properties and anti-microbial activities of chalcopyrite/wurtzite CuInS2 nanostructures synthesized via cyclic microwave irradiation

• Wurtzite CuInS 2 were synthesized without any additive. • Growth directions of hexagonal plates of wurtzite CuInS 2 were proposed. • Antimicrobial activities of CuInS 2 were investigated. CuInS 2 nanostructures were successfully synthesized by a cyclic microwave irradiation method at 600 W without adding any activated solvents or capping reagents. The pure CuInS 2 with the chalcopyrite and wurtzite crystal structures were obtained with the prolonged irradiation time as 30 and 75 cycles, respectively. The chalcopyrite CuInS 2 powders were nanoparticles with diameter of about 20–40 nm, and the wurtzite CuInS 2 powders were hexagonal plates with diameter of about 300–400 nm that preferentially grow along the < 01 1 ¯ 0 > directions. The optical properties of the synthesized CuInS 2 observed by UV–vis DRS spectra show their direct band gap energy of 1.48 eV. The anti-microbial activities of the synthesized CuInS 2 were investigated.

Optical absorption enhancement in ultrathin chalcopyrite solar cells with Ag reflective back contact

The optical performance of ultrathin solar cells based on chalcopyrite CuInS2 absorber has been studied, simulating the total absorption as a function of the absorber thickness with and without Ag reflective back contact. The structure chosen is ZnO:Al/SnS2/CuInS2/Ag/Mo/glass, using for the simulation the experimental data extracted from the layers prepared in our laboratory by evaporation (CuInS2 and SnS2) and sputtering (ZnO:Al, Ag and Mo). The main purpose has been to apply realistic input parameters (refractive index and extinction coefficient extracted from transmittance and reflectance measurements for each layer) to simulate and analyze the optical behavior of the entire device. It is found that the overall absorption of the cell with 0.2 μm-thick CuInS2 and 60 nm-thick Ag is the same as that obtained for 0.4 μm-thick CuInS2 without Ag layer. Thus, the incorporation of Ag reflective contact allows reducing the absorber layer thickness and therefore the time and cost of manufacturing chalcopyrite cells, being especially relevant for absorber thicknesses below 0.4 μm.

Synthesis and characterization of CuInS2 nanostructures and their role in solar cell applications

Copper indium sulphide (CuInS2) is regarded as an active material for solar cells owing to its unique optical properties, non-toxicity, low-cost and easy of synthesis. The cost and performance of the solar cell depend not only on the materials, but also on the preparation and fabrication techniques, which are significant for improving the efficiency of the device. In current study, the co-precipitation method was instigated to synthesize the chalcopyrite CuInS2 semiconductor nanoparticles (NPs) and the effects of annealing temperature on the size, agglomeration, functional groups and elemental compositions were investigated. In the next step, CuInS2 films were deposited on a conductive substrate using a stable dispersion by an electrophoretic deposition technique. Subsequently, the synthesized NPs and films were subjected to structural, morphological, optical and elemental analysis. X ray diffraction (XRD) revealed the formation of the tetragonal chalcopyrite CulnS2 NPs at 200 °C and 300 °C with the most prominent peak along the (112) orientation, and the calculated crystallite size ranged from 11.32 to 32.74 nm. Furthermore, the films were characterized by scanning electron microscopy, which showed the surface modifications of the electrophoretically deposited films at moderate voltage. The photovoltaic analysis shows that the cell fabricated at 90 V increases the cell's efficiency up to 1.27%, while the cells fabricated at 100 and 110 V increase the efficiency to 1.13% and 0.83%, respectively.

Systematic Study on Preparation of CuInS2 Films with Chalcopyrite from Nitrates

The Chalcopyrite CuInS2 films were prepared from nitrates below 220 °C. When the anhydrous ethanol is used as the solvent, the reaction cycle, temperature and holding time are main factors affecting crystallization. Increasing the reaction cycle, temperature and holding time are beneficial to the crystallinity. CuInS2 films prepared with thioacetamide and thiourea as sulfur sources have the chalcopyrite structure, the crystallinity of CuInS2 film prepared by thiourea is slightly better than that of by thioacetamide. It consists of spherical particles with diameters of 0.1 ∼ 0.4 μm. The band estimated gap of chalcopyrite CuInS2 film samples is about 1.49 ∼ 1.51 eV.

Experimental and Theoretical Study of Stable and Metastable Phases in Sputtered CuInS2.

The chalcopyrite Cu(In,Ga)S2 has gained renewed interest in recent years due to the potential application in tandem solar cells. In this contribution, a combined theoretical and experimental approach is applied to investigate stable and metastable phases forming in CuInS2 (CIS) thin films. Ab initio calculations are performed to obtain formation energies, X‐ray diffraction (XRD) patterns, and Raman spectra of CIS polytypes and related compounds. Multiple CIS structures with zinc‐blende and wurtzite‐derived lattices are identified and their XRD/Raman patterns are shown to contain overlapping features, which could lead to misidentification. Thin films with compositions from Cu‐rich to Cu‐poor are synthesized via a two‐step approach based on sputtering from binary targets followed by high‐temperature sulfurization. It is discovered that several CIS polymorphs are formed when growing the material with this approach. In the Cu‐poor material, wurtzite CIS is observed for the first time in sputtered thin films along with chalcopyrite CIS and CuAu‐ordered CIS. Once the wurtzite CIS phase has formed, it is difficult to convert into the stable chalcopyrite polymorph. CuIn5S8 and NaInS2 accommodating In‐excess are found alongside the CIS polymorphs. It is argued that the metastable polymorphs are stabilized by off‐stoichiometry of the precursors, hence tight composition control is required.

Theoretical investigation on the elastic and thermodynamic properties of CuInS2

The first-principles method based on the density functional theory is used to investigate the properties of chalcopyrite CuInS2 crystal. The crystal structural parameters are optimized, and the elastic constants and bulk modulus are also calculated, and the results are highly consistent with those in the literature. The stability of the crystal is judged from the Born stability criteria. Based on the quasi-harmonic Debye model, the pressure and temperature dependencies of the bulk modulus, the Debye temperature, the Gr?neisen parameter, and the thermal expansion coefficient are obtained.

The influence of posttreatment processes on the structures and the optical and electrical properties of CuInS2 and its heterojunction with various sulfides (CdS, CdZnS, and CdCuS)

As the first essential step toward understanding how to obtain an efficient CuInS2-based solar cell, this paper studied the photoelectric properties of CuInS2 and sulfide P–N heterojunction. For this purpose, the single-source evaporation method and the chemical bath deposition had been applied to prepare CuInS2 films and sulfide films (CdS, CdZnS, and CdCuS), respectively. The powder source was obtained from CuInS2 polycrystalline ingot, which consists of CuInS2 chalcopyrite phase. The segregated CuxS secondary phase on the surfaces of CuInS2 films could be removed by etching of bromine–methanol (BM) solution. The structures of ternary sulfide films (CdZnS and CdCuS) were similar to that of CdS film. The transient photocurrent of CdZnS thin film was highest, which might be related to the high reaction activity and the good crystal quality. Furthermore, the I–V response of CuInS2 and CdZnS heterojunction was studied, which was close to the ideal diode type behavior. The low reverse saturation current density, the optimal diode ideality factor, and the high barrier height were obtained from the I–V curve of CuInS2 and CdZnS heterojunction, which might mean that the CdZnS film could be suitable to use in photovoltaic application.

On the chemistry of grain boundaries in CuInS2 films

Abstract We conducted correlated transmission Kikuchi diffraction and atom probe tomography measurements to investigate the relationship between the structure and chemistry of grain boundaries in Cu-rich and Cu-poor sulfide chalcopyrite CuInS2 thin-films. We detect different elemental redistributions at random high‐angle grain boundaries, Σ9 twin boundaries and stacking faults in the Cu-rich and Cu-poor film but no chemical fluctuations at Σ3 twin boundaries. For the Cu-rich CuInS2 thin-film, our atom probe tomography analyses reveal Cu enrichment as well as In and S depletion at random grain boundaries, Σ9 twin boundaries and stacking faults. Hence, we may observe a ‘Cu on In’ scenario, which is accompanied by co-segregation of Na and C. In contrast, for the Cu-poor CuInS2 thin-film, our analyses show Cu depletion and In enrichment at random grain boundaries and at the vast majority of stacking faults. For S we do not observe a clear trend. Therefore, for the Cu-poor CuInS2 thin-film we may observe a ‘In on Cu’ scenario, which is accompanied by co-segregation of Na, K and O at the random grain boundaries but not at stacking faults. The amount of impurity segregation varies from one grain boundary to another in both thin-films.

Effect of Composition on the Optical and Electrical Conductivity of CuIn(SexS1−x)2

Optical and electrical conductivity of chalcopyrite CuIn(SexS1−x)2 (0 ≤ x ≤ 1) amorphous thin films are investigated. A transmission has been measured in a wavelength range (200 ≤ λ ≤ 2500 nm). The calculated optical energy band gap (Eg) and Urbach tail (band tail width) Eu decrease with increasing Se content. Refractive index (n) is estimated according to the Wemple–DiDomenico single oscillator model. Oscillator energy (E°), dispersion energy (Ed), and the ratio of free carrier concentration to electron effective mass (N/m*) are calculated from optical data for all thin films. Also, the high frequency dielectric constant at an infinite wavelength (e∞), lattice high frequency dielectric constant (eL) and static refractive index (n°) are determined. Electrical conductivity (σ) is obtained at room temperature.

Dispersive optical constants and electrical properties of nanocrystalline CuInS2 thin films prepared by chemical spray pyrolysis

Nanocrystalline CuInS2 thin films were deposited on borosilicate glass substrates via chemical spray pyrolysis method. The structural, morphological, optical, and electrical properties were studied as a function of increasing annealing temperature from 250 to 350 ̊C. XRD analysis showed mixed phases at lower temperatures with the preferred orientation shifting towards the (112) chalcopyrite CuInS2 plane at higher substrate temperature. The crystallite size increased slightly between 13 and 18 nm with increase in annealing temperature. The optical band gap was determined on basis of Tauc extrapolation method and the Wemple–Di-Domenico single oscillator model. Possible structural and quantum confinement effect may have resulted in relatively larger band gaps of 1.67–2.04 eV, relative to the bulk value of 1.5 eV. The presence of CuxS in the as-deposited and wurtzite peaks after annealing at 350 ̊C play a role in influencing the optical and electrical properties of CuInS2 thin films.

Mo/CIGS/CdS Structures by E‐ALD

The chalcopyrite CuIn(1‐x)GaxSe2 (CIGS) thin films and their cadmium sulfide (CdS) window layer structures (CIGS/CdS) were grown on Mo foil substrate in layer‐by‐layer fashion by electrochemical atomic layer deposition (E‐ALD) and were characterized by X‐ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and photoelectrochemical (PEC) activity. XRD shows distinct pattern changes from chalcopyrite to chalcopyrite plus CdS structures upon adding E‐ALD CdS layer to CIGS layers on Mo substrate. SEM shows that uniform and homogeneously distributed nanoparticles of CdS formed on top of CIGS layers, and EDS shows the successful preparation of CIGS/CdS structures with good atomic ratios in each layer. PEC performance reveals that bare CIGS films were of p‐type conductivity but that CIGS/CdS structures n‐type with p‐type response near null.

Green and room-temperature synthesis of aqueous CuInS2 and Cu2SnS3 nanocrystals for efficient photoelectrochemical water splitting

In this work, green synthesis of aqueous ternary CuInS2 (CIS) and Cu2SnS3 (CTS) nanocrystals has been realized by a simple one-pot mixing route. The synthesis is performed at room temperature without using long-chain capping agents, possessing ecofriendly, low-cost and low-energy-consuming merits. The chalcopyrite CIS nanocrystals with a size of 3–5 nm exhibit a prominent photoluminescence peak at 713 nm, revealing a bandgap of 1.74 eV. Sensitization of the nanocrystals on the surface of ZnO nanorod arrays is achieved through spin-coating followed by thermal treatment. Both the CIS and CTS nanocrystals-sensitized ZnO nanorod arrays grown on F-doped tin oxide (FTO) glass substrates are utilized as the photoanodes for efficient photoelectrochemical (PEC) water splitting. After sensitization, the photocurrent density at 1.23 V vs. NHE increases from 0.46 mA cm−2 for the bare ZnO photoanode to 5.98 mA cm−2 for the ZnO/CIS photoanode and 4.85 mA cm−2 for the ZnO/CTS photoanode under one Sun illumination. The significant enhancement in PEC performance is attributed to the expanded optical absorption throughout the visible light region and the stepwise energy band alignment between ZnO and CIS/CTS facilitating for fast charge separation and transport. Our work demonstrates an appealing strategy to synthesize aqueous ternary nanocrystals by green chemistry for efficient solar energy conversion devices.

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.

Formation of Colloidal Copper Indium Sulfide Nanosheets by Two-Dimensional Self-Organization.

Colloidal 2D semiconductor nanosheets (NSs) are an interesting new class of materials due to their unique properties. However, synthesis of these NSs is challenging, and synthesis procedures for materials other than the well-known Pb- and Cd-chalcogenides are still underdeveloped. In this paper, we present a new approach to make copper indium sulfide (CIS) NSs and study their structural and optical properties. The CIS NSs form via self-organization and oriented attachment of 2.5 nm chalcopyrite CuInS2 nanocrystals (NCs), yielding triangular- and hexagonal-shaped NSs with a thickness of ∼3 nm and lateral dimensions ranging from 20 to 1000 nm. The self-organization is induced by fast cation extraction, leading to attractive dipolar interactions between the NCs. Primary amines play a crucial role in the formation of the CIS NSs, both by forming in situ the cation extracting agent, and by preventing the attachment of NCs to the top and bottom facets of the NSs. Moreover, DFT calculations reveal that the amines are essential to stabilize the covellite crystal structure of the product CIS NSs. The NSs are indium-deficient and the off-stoichiometry gives rise to a plasmon resonance in the NIR spectral window.

Systematic Investigation on Synthesis of CuInS2 Powder and its Influencing Factors

AbstractCuInS2 powders were prepared by solvothermal method. The effects of experimental conditions on crystal structure, composition phase and morphology were investigated systematically. The phases of product samples were analyzed by X‐ray diffraction (XRD) on the Bruker D8 Advance XRD system with Nifiltered Cu‐Kα (λ = 1.5059 Å). The morphology of the product powders were observed using scanning electron microscope (SEM) with a model of JSM‐6380LA made by Japan Electronics Co., Ltd. The elemental compositions of the product powders were analyzed by energy dispersive spectroscopy (EDS). The results show that, different solvents have important effects on the crystal structures of CuInS2 powders. With CuC12·2H2O, InCl3 and SC(NH2)2 as raw materials, the wurtzite CuInS2 obtained with the mixed solvent of ethanol and hydrazine hydrate has better crystallinity than that obtained by the mixed solvent of ethylene glycol and hydrazine hydrate. The product powder obtained with ethanol without hydrazine hydrate has major phase chalcopyrite CuInS2. The wurtzite CuInS2 powder consists of aggregated particles with diameters of 0.1 ∼ 0.5 μm. The sample with chalcopyrite has relatively more large particles with diameters of 3 ∼ 5 μm which consist of smaller flakes. The optimum conditions for preparing wurtzite CuInS2 powder are at 160 °C for 20 h using CuC12·2H2O, InCl3 and SC(NH2)2 as raw materials and the mixed solution of ethanol and hydrazine hydrate as solvent. With the increase of reaction temperature, the XRD peaks of chalcopyrite CuInS2 are more obvious, but the new impurity phase Cu2S appears at 220 °C. With holding time prolonging, it is helpful to eliminate the XRD peaks of impurity and promote chalcopyrite CuInS2 formation. The optimum conditions for chalcopyrite CuInS2 are reacting at 220 °C for 30 h with ethanol without hydrazine hydrate as solvent and CuC12·2H2O, InCl3 and SC(NH2)2 as raw materials.

The effect of processing on the properties of CuInS2 nanomaterials synthesized by simple hot injection route

Chalcopyrite and wurtzite CuInS2 (CIS) nanomaterials were synthesized from Cu[Formula: see text], In[Formula: see text], thiourea with or without triethanolamine (TEA) by simple hot injection method at low temperature. The effect of synthesis duration on the various properties of the synthesized CIS nanomaterials was studied. It shows that for chalcopyrite CIS, the optimal synthesis duration is 60 min and the synthesized nanomaterial is in spherical shape with diameter of about 90 nm. However, for the wurtzite CIS, the optimal synthesis duration should reach 150 min and the synthesized nanomaterial looks like nanoplate with thicknesses of [Formula: see text]10 nm and diameters near 100 nm. The photovoltaic characteristics of two types of nanomaterials are quite different. This study may contribute to the synthesis of CIS nanomaterials at low temperatures.

Effect of structural phase transformations under pressure on electronic and optical properties of CuInS2

First-principles plane-wave calculations were employed to study the phase transitions, electronic and optical properties of chalcopyrite CuInS2 (CIS) under pressure, which is a promising semiconductor compound material for nonlinear optical, photovoltaic and bio-applications. From the variations of Gibbs free energy and volume with pressure, we confirmed an experimentally found phase transformation of CIS from tetragonal I4¯2d structure into the cubic Fm3¯m phase. It occurs at 7.9 GPa with a volume reduction of 15.6%, which are comparable with the experimental values of 9.5 GPa and 12%. A new possible phase transition of CIS from the cubic Fm3¯m structure to the orthorhombic Cmcm structure under higher pressure was predicted occurring at 49.6 GPa with a volume reduction about 0.64%. Using the more accurate HSE06 functional, we found that the growth rate of energy gap with pressure (dEg/dP) for the I4¯2d phase is about 24.8 meV/GPa, very close to the experimental value of 24 meV/GPa. The calculated electronic properties for Fm3¯m and Cmcm phases show that CIS is a metallic material under high pressure, rather than a semiconductor. The optical absorption spectra indicate that with the increase of pressure the absorption edge of CIS becomes smaller while the optical energy gap is larger.

Systematic survey of suitable buffer and high resistive window layer materials in CuIn1−xGaxSe2 solar cells by numerical simulations

This work investigates the impact of opto-electronical buffer (b) and high resistive window layer (w) properties, i.e. band gap Eg(b,w) and electron affinity χe(b,w), on the device performance of chalcopyrite CuIn1−xGaxSe2 (CIGS) solar cells by numerical simulations with SCAPS. We established an initial device model based on an experimental device and its J–V, C–V, and EQE data at room temperature as well as its quantified depth profile for the [Ga]/([Ga]+[In]) ratio (GGI). The device features a non-uniform CIGS doping profile as well as a strongly doped CIGS surface layer. Based on our simulations that include various buffer layer materials, we argue that the most suitable buffer and window layer is Zn1−zMgzO. The potential gain in efficiency is up to 0.9% absolute which corresponds to a relative gain of 4.1%.

Lattice Dynamical Properties and Elastic Constants of the Ternary Chalcopyrite Compounds CuAlS2, CuGaS2, CuInS2, and AgGaS2

Lattice dynamics calculations have been performed for ternary chalcopyrite compounds CuAlS2, CuGaS2, CuInS2, and AgGaS2 using the proposed theoretical model. This model is applied to study the zone-centre (GAMMA = 0) phonon frequencies of CuAlS2, CuGaS2, CuInS2, and AgGaS2. The interatomic interactions up to third nearest neighbours were calculated. The calculated zone-centre phonon frequencies are found to be in very good agreement with observed and previous calculated data available in the literature. Single crystal elastic constants and related properties for these materials were also calculated and compared with the available data in the scientific literature.

Solution-based synthesis of dense, large grained CuIn(S, Se)2 thin films using elemental precursor

Compared with the expensive and complicated vacuum techniques, the solution-based process to deposit I-III-VI2 chalcogenide thin films (I=Cu, III=In or Ga, VI=S or Se) has attracted great interests due to its lower cost, higher scalable production and better application in flexible substrate. Herein, a low-toxic and high-active mixture solvent comprised of 1, 2-ethanedithiol and 1,2-ethylenediamine is utilized to dissolve elemental Cu, In and S powders at 60°C, forming the CuInS2 (CIS) precursor solution. After spin coating and annealing in a both Ar gas and selenium atmosphere, a dense and large-grained chalcopyrite CuIn(S,Se)2 (CISSe) thin films with a close-packed grain size of ~800nm are prepared, eliminating a undesired fine fine-grained bottom layer. In addition, the selenization temperature of the CISSe thin films is also discussed, which influences the phase composition, crystallinity and morphology of CISSe thin films. Photovoltaic device of the CISSe-based thin films is fabricated, obtaining a power conversion efficiency of 6.2% with an active cell area of 0.5cm2 under AM 1.5 illumination.