CuInS2 Thin Films Research Articles

Photoelectrochemical Hydrogen Production from Water Using Copper‐based Chalcopyrite Thin Films

AbstractCopper (Cu)‐based chalcopyrite compounds are promising photoabsorber materials not only for solar cells but also for photoelectrochemical (PEC) systems for conversion of sunlight energy into chemical energy. PEC water splitting to generate hydrogen (H2) is one of the most advanced technologies in a PEC system for the use of Cu‐based chalcopyrite compounds. In this review, we firstly introduce crystallographic/energetic structures of Cu‐based chalcopyrite compounds in view of their applications to PEC water splitting. Explanations for the operation of PEC water splitting using semiconductor materials are then overviewed. Based on these backgrounds, studies on PEC H2 evolution over photocathodes based on CuInS2 and CuGaSe2 thin films that we have developed are reviewed in detail. For realizing efficient PEC H2 evolution over these thin films, surface modifications with an n‐type layer such as CdS and a catalytic site such as Pt deposit were found to be indispensable. Precise controls of p‐n heterointerfaces formed by introducing an n‐type layer should also be required to enhance PEC performance. Although PEC water splitting has not reached the required efficiency to be useful, effective combinations of appropriate surface and interface modifications should lead to further improvements of properties to be close to practical applications.

Studies of Undoped and Doped Films of CuInS2

To find out the effect of the rare earth doping element Holmium (Ho) on CuInS2 thin films, various studies have been carried out and the results have been reported in this paper. The PL study shows that intensity of doped film is more than undoped film. The PL emission peak appears at 570–580 nm. SEM images of CIS:Ho (4 ml) film shows agglomeration on the surface. Both synthesized film of CuInS2 appears to be amorphous in nature with chalcopyrite structure as clear from XRD. Hall measurement and optical studies were also performed.

Electro-optical characterization of rare earth doped CuInS2 thin films synthesized by CBD

This work aims to study the electrical and optical properties of CuInS2 thin films to see the impact of rare earth doping on the properties of films obtained by Chemical bath deposition (CBD) in alkaline medium at 80 °C bath temperature. The observed and calculated lattice parameters are in good agreement with each other as confirmed from structural studies. Hall mobility and other parameters were calculated. The mobility of Pr doped film was quite high. E = hν = hc λ has been used to calculate the band gaps of various doped films of CuInS2. It is found that band gap is low for Sm doped film. This could be due to small particle size. Presence of dopant has been confirmed from EDS. PC studies has been done to know about the possible states in band gap. The photoconductive gain is high in Sm doped film. The emission spectrum were recorded for the wavelength 300–1000nm. The peak sharpness in terms of intensity is very high in Sm doped films. Spherical shape particles are prominently appeared on the surface of the film.

Improving FTO/ZnO/In2S3/CuInS2/Mo solar cell efficiency by optimizing thickness and carrier concentrations of ZnO, In2S3 and CuInS2 thin films using Silvaco-Atlas Software

Optimization of optical and electrical properties of active semiconducting layers is required to enhance thin film solar cells' efficiency and consequently became the cornerstone for sustainable energy production. Computational studies are one of the ways forward to optimize solar cells’ characteristics. In this study, Silvaco-Atlas, a powerful software that excels in both 2D and 3D electrical simulations of semiconductors has been used for the simulation in order to investigate the solar cell properties. The architecture of the solar cell simulated was FTO/ZnO/In2S3/CuInS2/Mo. This study aims to optimize solar cell efficiency by optimizing film thicknesses and carrier concentrations via simulation. The designed solar cell was exposed to the presence of a sun spectrum of AM1.5 from a 1kW/m2 incident power density at 300K. The thickness values of the window (ZnO), absorber (CuInS2) and buffer (In2S3) layers were varied to record a solar cell's optimum thickness. The resulting FTO/ZnO/In2S3/CuInS2/Mo solar cell formed by simulation is presented. The best efficiency and fill factor of the solar cell simulated were found to be 41.67% and 89.19%, respectively. The recorded values of current density and the open circuit voltage of the cell were 40.33mA/cm2 and 1.15 V, respectively. Additionally, the maximum power of the simulated solar cell device was 41.68 mW. Optimization results revealed that the most efficient cell found was made up of a window layer with a thickness of 0.03μm, an absorber layer with a thickness of 6.0μm and a buffer layer with a thickness of 0.2μm. The optimized carrier concentration of ZnO, In2S3 and CuInS2 was respectively 1e21 cm-3, 1e20 cm-3, 3e18 cm-3 and the optimized Al-doped ZnO value was 1e25 cm-3. The Absorption spectra indicated that the solar cell's peak absorption occurs between 350 nm and 1250 nm and presented a good external quantum efficiency (EQE) of around 84.52% to 92.83% which indicates good efficiency in the visible domain. This performance is attributed to the transparency of FTO, ZnO and good absorption of In2S3 and CuInS2 thin films.

Experimental and theoretical study of electrodeposited CuInS2 thin films for solar cell applications

Absorbent CuInS2 layers were successfully prepared using an electrodeposition technique on ITO-coated glass, followed by a sulfidation process. The effects of sulfurization time on the structural, morphological and optical properties of samples were examined. The structure, morphology, and composition of synthesized films were characterized by using X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectrometer (EDS), while the optical properties were examined by UV-VIS-NIR spectrophotometry. The experimental results show that the resulting films (CIS) are polycrystalline with a chalcopyrite structure with a preferential orientation along the (112) plane and show that Cu atoms separate near the grain boundaries and a wide bandgap value of 1.52 eV. The SEM study showed that the surface of the CIS films was dense and uniform. Theoretical calculations carried out by TB-mBJ showed a wide bandgap of 1.15 eV, a high refractive index, and absorption coefficient in the visible region which is consistent with the experimental results found.

Synthesis of CuInS2 thin film photocathode with variation of sulfurization sources and Pt-In2S3 modification for photoelectrochemical water splitting

CuInS2 thin films have been successfully synthesized from the electrodeposition of copper (Cu), indium (In), and sulfurization on a molybdenum glass substrate as a water splitting photocathode. The effect of various sources of sulfurization with thiourea, sulphur, and H2S and modification with Pt-In2S3 on the character and performance of the material was observed. The success of the synthesis was confirmed by the typical peaks of 28.2, 46.8, and 55.4° on XRD, the presence of Cu, In, S elements on SEM-EDX analysis, the appearance of peaks of 298 cm−1 on Raman analysis, and the detection peaks of Cu 2p, In 3d, and S 2p with XPS analysis. Meanwhile, performance effectiveness and photoelectrochemical properties were analysed with photocurrent linear sweep voltammetry (LSV), applied bias photon-to-current efficiency (ABPE), and incident photon-to-current conversion efficiency (IPCE). Variations of sulfurization sources give different character and photocurrent results due to differences in the existing reaction mechanisms. While the modification treatment with Pt-In2S3 increased the resulting photocurrent. Sulfurization with H2S and modification of Pt-In2S3 gave the best results with a photocurrent of 18 mA cm−2, an efficiency of 3% ABPE, 47.2% IPCE, was evolved 467 μmol H2 and 230,1 μmol O2. This shows good potential as a water splitting material to produce environmentally friendly hydrogen fuel.

The upsurge of absorption coefficient in CuInS2 thin film with Ru doping: an energetic absorber layer in a superstrate solar cell

In this work, a clear increase in electrical mobility and absorption coefficient has been demonstrated in spray pyrolysis-deposited CuInS2 (CIS) thin films by ruthenium (Ru) doping. This film was then employed as an efficient absorber layer in superstrate photovoltaic cells for the first time. Ru doping into the CIS tetragonal crystal structure increases the tensile strain causing structural modifications including average crystallite size and dislocation density. Further, the Ru causes an adjustment in the Brillouin zone boundary of the CIS semiconductor leading to alternative morphologies on the surface of the substrate such as particles (2 wt%), rods (4 wt%), and leaf-like mixed nanoparticles (6 wt%). The absorbance and emission properties of this CIS absorber layer were studied for possible enhancement in optical properties due to the surface modification. A higher absorption coefficient (1.20 × 106 cm−1 compared to pristine CIS 0.84 × 106 cm−1) was observed in the Ru-doped CIS film. The possibility for Ru-4d to S-3p transition explains the electronic origin of an enhanced absorption coefficient in Ru-doped CIS thin films. The atomic elements such as Cu, In, S, and Ru and their corresponding 1+, 3+, 2−, and 4+ oxidation states remained unchanged following doping illustrating an intact lattice. The Ru-doped CIS films, optimized at 6 wt%, exhibited both higher electrical and photo responses as compared to a pristine CIS film. Solar cells were fabricated using the ITO/AZO/CdS/CuInS2 superstrate configuration with and without the Ru doping (0 and 6 wt% Ru-doped CIS)/Au showing an increase from 2.84% to 4.46% PCE a 1.62% increase overall. Following this, similar durability over 500 h was observed in both device types.

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.

In situ one-step synthesis of CuInS2 thin films with different morphologies and their optical properties

In situ one-step synthesis of CuInS2 thin films with different morphologies and their optical properties

Low Temperature Ink-Based Cuins2 Thin Films for Photoelectrochemical Water Splitting and Photovoltaic Applications

Low Temperature Ink-Based Cuins2 Thin Films for Photoelectrochemical Water Splitting and Photovoltaic Applications

Tunable structural, morphological and optical properties of undoped, Mn, Ni and Ag-doped CuInS2 thin films prepared by AACVD

The preparation of high-quality copper indium sulphide, CuInS2 photo-absorber material with tunable properties for efficient, low-cost, thin film solar cells using scalable methods remains a challenge. In order to address this, high quality off-stoichiometric undoped and Mn, Ni and Ag-doped CuInS2 (CIS) thin films have been deposited onto glass substrates by aerosol-assisted chemical vapour deposition (AACVD) using metal diethyldithiocarbamate precursors at temperatures of 350, 400 and 450 °C. Data from powder X-ray diffraction (p-XRD), Raman spectroscopy and scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS) suggest a correlation of morphology and composition of tetragonal phase (chalcopyrite and copper-gold-type) sulphur-deficient microcrystalline CIS thin films. For undoped thin films, near-infrared optical absorption and emission with tunable band gap between 1.32 and 1.42 eV are likely associated with donor-acceptor pairs involving deep or shallow electronic states such as sulphur vacancies (VS••), indium-copper anti-sites (InCu••) and indium interstitials (Ini•••) as donors and copper vacancies (VCu′) as acceptors. Whilst Mn-doped thin films exhibit minimal tunable properties, Ni and Ag-doped films exhibit tunable morphology, composition and near-infrared absorption for small dopant content. Though further studies are required to explore the defect chemistry, these results show the utility of AACVD in tuning structural, morphological and optical properties of undoped, Mn, Ni and Ag-doped CIS thin films.

CuFeO2/CuInS2 Composite Thin Film Photocathode Prepared by Template Method for CO2 Conversion Into Methanol

The huge consumption of fossil fuels in industrialization has caused increasingly aggravated greenhouse effect. To address this problem, converting CO2 into liquid solar fuels by photoelectrochemical technology is highly expected. In order to enhance the photoelectrochemical performance of the photocathodes, the composite thin film photocathodes have been constructed by covering CuFeO2 nanoparticles (CFO NPs) on CuInS2 (CIS) thin film surface by the impregnation (I-CFO/CIS) and the template method (T-CFO/CIS). In addition, the p–p heterostructure is formed between CIS and CFO NPs. Furthermore, the adsorption behaviors of intermediates are altered because of the well dispersed and smaller size of CFO NPs on T-CFO/CIS thin films. As a result, enhanced photoelectrocatalytic CO2 reduction is achieved. The yield of methanol on T-CFO/CIS thin film reaches up to 270 μM, which is 3.5 and 11.2 times as high as that on I-CFO/CIS and CIS thin films, respectively. At the applied voltage of −0.65 V vs saturated calomel electrode (SCE), the maximal faradic efficiency of methanol on T-CFO/CIS photocathodes is as high as 87%.

Fabrication of metal chalcogenide thin films by a facile thermolysis process under air ambient using metal-3-mercaptopropionic acid complex

We report a facile and low-cost solution-based approach to synthesize various binary, ternary and quaternary metal chalcogenide thin films. Homogeneous metal chalcogenides single precursor is prepared by dissolving metal salt (metal chloride/acetate) in ethanolic/methanolic solution of 3-Mercaptopropionic acid (MPA) at room temperature. High-quality CdS, ZnS, Sb2S3, CuInS2 (CIS) and Cu2ZnSnS4 (CZTS) metal sulfide thin films are successfully synthesized by thermalizing these metal-MPA precursor solution at 350 °C in air for 15 min. The mechanism of metal sulfide formation is analyzed by FTIR and thermogravimetry coupled with mass spectrometry. This study highlights the formation of intermediate metal-MPA complex as a single precursor, which eventually decomposes into metal sulfide upon heating at 350 °C. The film thickness, morphology and composition of metal sulfide can be controlled by the concentration of reactants, deposition cycles and the choice of solvent. XRD, Raman, UV–vis spectroscopy, diffuse reflectance spectroscopy and energy dispersive analyses ascertain the phase purity of the films. Bandgap estimates, morphology, narrow Urbach width with low defect densities in the bandgap region, uniform thickness discerned from cross-section SEM, uniformity in the elemental maps and the photoconductivity studies further confirm high-quality of the films. Attaining molecular-level homogeneous precursor solution and inertness to the air ambient enables precise control on the stoichiometry and the enhanced uniformity of deposited films. This facile method will have potential application in large scale synthesis of different metal chalcogenide thin films by a thermolysis process and is highly suitable for controlling stoichiometry and spatial uniformity of deposited films sought in solar cell, optoelectronic and catalysis applications.

Structural and optical properties of Pr doped CuInS2 thin films synthesized by chemical bath deposition

The Pr doped CuInS2 thin films have been prepared by chemically bath deposition technique at 80°Ctemperature. The semiconducting films are grown in bath containing aqueous solution of copper (II) chloride dihydrate, Indium (III) chloride, thiourea, TEA, ammonia (25%). Pr is used as the doping element. Chloride dehydrates is used for the copper ion source, Indium chloride for indium ion source and thiourea for sulphur ion source, TEA is a complexing agent and ammonia maintains the pH. The SEM Studies of Pr doped CuInS2 films show that at lower volume polyhedral shaped particle appears on the surface. No voids are seen. But at higher volume of Pr; voids are seen on the surface. Particle looks like accumulated woolen balls or cubic like grains. Agglomeration of particle increases with volume and hence particle size also increases. In the XRD of prepared sample characteristic peaks of chalcopyrite phase appears between (240- 800) in all the films. Hall measurement shows that resistivity of Pr (6ml) doped film is very high. The conductivity of all doped films is higher than undoped film. In general, increased doping will leads to increased conductivity. In the Photoluminescence study the emission peak appears at wavelength 575nm, 550nm and 525nm wavelength. High transmittance, low reflectance found in the visible region in the entire prepared sample. The absorption peaks fall in the visible region. High Photocurrent is found, and in dark current study the linear behavior between voltage and current are seen. Quite good photosensitivity is observed in Pr doped CuInS2 films.

A novel low-temperature growth of uniform CuInS2 thin films and their application in selenization/sulfurization-free CuInS2 solar cells

In terms of manufacturability, there is a high tendency to deposit light-absorbing CuInS2 films by solution processing methods like ink-based depositions. In particular, for nanoparticle inks, the synthesis of highly dispersed and stable inks, with uniformity in the deposition process, is a serious challenge. Here, we demonstrate a novel two-step low-temperature CuInS2 film deposition method in which the In2S3 is deposited first. It then partially is converted into CuInS2 through the infiltration of Cu+ ions in the In2S3 layer in a dip-coating process. The resulting films are highly uniform, with diffraction peaks indicating the formation of pure CuInS2 phase. The proper stoichiometry of CuInS2 layers is confirmed by the optical absorption spectrum, energy–dispersive x-ray spectroscopy, and X-ray photoelectron spectroscopy analysis. Our Cd-free devices are structured by FTO/TiO2/In2S3/CIS/carbon, in which the residual In2S3 film acts as a buffer layer. The results demonstrate that the planar superstrate CuInS2 solar cell with the optimized absorbing layer composition has a power conversion efficiency of 2.11 %, which is the highest reported efficiency for a low-temperature solution-based selenization/sulfurization-free CuInS2 device structures prepared by ion-exchange method.

Photo-electrochemical CO2 reduction at CuInS2 thin-film cathodes modified with CuIn alloy particles derived from Cu2O particles

ABSTRACT In order to reduce CO2 to ethanol, the CuIn alloy-particle modified CuInS2 (CuIn AP/CIS) composite thin-film electrodes have been suggested and their catalytic activity and selectivity have been examined. The CuIn AP/CIS composite thin films have been fabricated via by two-step electrodeposition route – electrodepositing the Cu2O particles on the CuInS2 thin films, followed by electrodeposition of metallic indium on the Cu2O/CuInS2 thin films. Compared to the Cu2O/CuInS2 composite thin-film electrode, the CuIn AP/CIS composite thin-film electrode exhibits high catalytic activity and selectivity for ethanol formation. At the CuIn AP/CIS composite thin-film electrode with electrodeposition of In for 30 s, ethanol concentration reaches 0.046 mM at 1.5 h. The results of the electrochemical impedance spectra show that the interface charge-transfer is the rate-determining step in the CO2 reduction process, and the CuIn AP/CIS composite thin-film electrode with electrodeposition of In for 30 s exhibits the smallest resistant of the interface charge-transfer. The study on the adsorbed intermediates shows that the surface modification of CuIn AP increases *CO coverage and decreases *H coverage significantly, thus promoting coupling of *CO. Therefore, the selectivity for ethanol formation is improved.

Effect of substrate type on RF magnetron sputtered CuInS2 thin films properties based on nanoparticles synthesized by solvothermal route

Stereometric and fractal analyses have been performed on the three-dimensional surface microtexture of the sputtered copper indium disulfide films on various substrates. The target used in the sputtering was made from nanoparticles synthesized by the solvothermal route. The effects of substrate on structural and morphological properties of the films were investigated. The obtained CuInS2 films were polycrystalline textured, preferentially oriented in (112) crystallographic direction. Also, the (112) peak intensity changes with the substrate type. From atomic force microscopy (AFM) analysis, it can be concluded that the growth of the film on molybdenum substrate is promising for photovoltaic applications particularly as absorber layer in solar cells. The surface microtexture characterization in terms of surface dimensions, volume, curvature, shape was analyzed according to ISO 25,178–2: 2012 standard.

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.

Electrospray preparation of CuInS2 films as efficient counter electrode for dye-sensitized solar cells

In this study, CuInS2 (CIS) thin films were prepared via electrospray (ES) method using a stable CIS nanoparticle dispersion with the assistance of thiourea additive. When the optimized CIS film was utilized as counter electrode (CE) for dye-sensitized solar cell (DSSC), a PCE of 8.81% was achieved under AM 1.5 illumination (100 mW cm−2), constituting over 13% improvement compared with platinum (Pt) control-device and being the highest among CIS based DSSCs. Further analyses show that the porous network in CIS film and the close contact between the FTO and the CIS film may account for the improvement because it not only offers more sites for efficient catalysis of redox couples in the electrolyte but also promotes charge transfer in the DSSC device. Moreover, the CIS film in the DSSC device was also proved to contribute to the photocurrent generation. This work firstly demonstrates the capability of ES method to fabricate CIS films and proves that the ES-prepared CIS film is a promising alternative to Pt CE in DSSC devices. Furthermore, this method can be adopted to prepare the CIS absorber in thin-film solar cells, as well as to prepare functional films based on other semiconductors.

Influence of deposition parameters on surface morphology and application of CuInS2 thin films in solar cell and photocatalysis

Copper indium disulfide (CuInS2) thin films as an absorption layer for solar cell and photocatalytic degradation of organic pollutants, were successfully electrodeposited on the FTO coated glass substrate using the simple and inexpensive electrodeposition method and a sulfurization process. The effects of the Cu/In molar ratio, annealing temperature and kind of Cu2+ precursor (Cu(salen) and Cu(acac)2 as novel Cu2+ precursors) on the structural and morphological properties of samples were examined. The XRD diffraction patterns and energy dispersive spectroscopy measurements exhibit that high-quality film with superior crystalline structure was formed in the presence of Cu(salen) as Cu2+ precursor. Also, we found that a suitable heat treatment temperature could suppress the CuS phases and form well-crystallized CIS. As we know, this is the first reported efficiency for any CuInS2 superstrate solar cell to date that fabricated using Cu(salen) as Cu2+ precursor. In addition, the photocatalytic degradation of organic dye in the presence of as-synthesized CuInS2 thin films was studied. The as-prepared semiconductor photocatalysts have a good reusability; it can be successfully reused for 5 times recycling photoactivity tests.