CuInS2 Films Research Articles

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.

Preparation and Structural Characterization of Thin Films of CuInS2 by Sintering Colloidally Synthesized Nanoparticles at Moderate Temperature

Copper indium disulfide nanoparticles continue attracting attention as absorber material in light harvesting devices. The preparation of thin films by deposition of this material from colloidal solution remains challenging. Typically, colloidal semiconductor nanoparticles are surrounded by long organic ligand molecules which are required to stabilize the particles during synthesis. A common way to obtain conductive thin films is the development of ligand exchange procedures that need to be applied prior to film deposition. However, in the case of copper indium disulfide nanoparticles, appropriate procedures are still missing. Therefore, an alternative approach is investigated herein. Colloidal copper indium disulfide nanoparticles are synthesized and deposited on substrates. Instead of applying a ligand exchange procedure, thermal removal of the ligands and sintering of the inorganic film are explored. Results on the preparation of the nanoparticle films, their structural investigation, and conductivity measurements are reported.

Photoelectrochemical and Photovoltaic Performance of As-deposited Ink-based CuInS2 Heterojunction Thin Film

In this report, we demonstrate low-temperature ink-based fabrication of CuInS2-based photoelectrodes for hydrogen production capable of producing photocurrent densities as high as 8.8 mA.cm−2. In this process, molecular ink made of metal chlorides and thiourea dissolved in methanol was spin coated onto Mo-coated soda lime glass substrates. Samples were then placed on a hot plate (sample surface temperature: 250 °C) to induce CuInS2 formation and remove the solvent and by-products. No further processing, such as high temperature sulfurization, was performed. The CuInS2 films were then integrated as photocathode for hydrogen evolution by photoelectrodeposition of Pt nanoparticles. Photocurrent density of 0.4 mA.cm−2 at 0 V vs. RHE was detected from such electrodes. However, samples coated with CdS/ZnO/ITO overlayers forming heterojunction prior to Pt deposition exhibited significant improvement of the photocurrent density, reaching 8.8 mA.cm−2 at 0 V vs. RHE, highlighting the improved charge transfer by the p-n junction formed at the CuInS2/CdS interface. The charge transfer resistance of the CuInS2/CdS/ZnO/ITO-Pt photoelectrode was almost 5 times lower than that of the CuInS2-Pt photoelectrode as revealed by electrochemical impedance spectroscopy analysis. In addition, the onset potential was shifted by ca. 0.45 V toward the anodic direction, reaching 0.75 V vs. RHE. Solar cell made of identical structure (Mo/CuInS2/CdS/ZnO/ITO) showed power conversion efficiency of 2.1% with short-circuit photocurrent density and open circuit voltage of 7.4 mA.cm−2 and 820 mV, respectively.

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.

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.

Optimization of selenization process to remove Ga-induced pin-holes in CIGS thin films

In thin-film solar cells, deposition of pinhole and the crack-free absorber layer, with the right chemical stoichiometry is highly important for high-performance solar cell devices. In solution-based CIGS solar cell technology, a nanoparticle ink approach provides phase stability of the final chalcogenide absorber layer. However, the sintering of small nanoparticles to form large grains with reduced grain boundaries is an important challenge in the fabrication process. This is usually realized by annealing in the Se atmosphere, i.e. selenization process. However, the presence of Ga in CIGS films leads to pinholes after selenization. In this study, the synthesis and deposition of high-quality films of CuInS2 (CIS) and CuIn0.75Ga0.25S2 (CIGS), are studied by using FESEM, XRD, EDS, and DLS characterization of CIGS and CIS nanoparticles and final films. We show that by selenization at reduced pressure and optimizing time and temperature, growing pinhole-free CIGS films with large grains is possible.

Self-powered anti-interference photoelectrochemical immunosensor based on Au/ZIS/CIS heterojunction photocathode with zwitterionic peptide anchoring

Accurate detection of important biomarkers with ultra-low levels in complex biological matrix is one of the frontier scientific issues because of possible signal interference of potential reductive agents and protein molecules. Herein, a self-powered anti-interference photoelectrochemical (PEC) immunosensor was explored for sensitive and specific detection of model target of cardiac troponin I (cTnI). Specifically, a novel ternary heterojunction served as the photocathode to offer a remarkable current output and a zwitterionic peptide was introduced to build a robust antifouling biointerface. CuInS2 (CIS) film with porous network nanostructure was first prepared and then modified in order with ZnIn2S4 (ZIS) nanocrystals and Au nanoparticles to fabricate the Au/ZIS/CIS heterojunction photocathode. After capture cTnI antibody (Ab) was immobilized, the zwitterionic peptide KAEAKAEAPPPPC was then anchored to compete the immunosensor. The elaborated PEC immunosensor exhibited high sensitivity for target cTnI antigen (Ag) detection, with good anti-interference against reductive agents and nonspecific proteins. This integration strategy of heterojunction photocathode with zwitterionic peptide provides a new sight to develop advanced PEC immunosensors applying in practical biosamples.

Pre-deposited alkali (Li, Na, K) chlorides layer for effective doping of CuInSSe thin films as absorber layer in solar cells

We introduce an effective method for copper indium sulfide selenide (CISSe) doping with different alkali metals (Li, Na and K) based on a pre-deposited alkali chloride layer. A simple and fast spray method is used for pre-deposition of alkali chloride layer (LiCl, NaCl, KCl) on substrate surface before spray pyrolysis deposition of copper indium disulfide CuInS2 (CIS) films followed by selenization. The different properties of alkali-doped CISSe films by the alkali chloride pre-deposition (ACPD) method were compared to the post-deposition treatment (PDT) method. Based on FESEM images, a highly compact film with large grains can be obtained for CISSe films doped with K(∼0.72 μm) and Na (∼0.56 μm) by the ACPD method that is considerably higher than un-doped films (∼0.47 μm). While for the PDT method, grain size decreased after the doping process. UV–Vis analysis showed that alkali atoms with larger size result in more band gap widening of CISSe film. According to Mott-Schottky results, all films are p-type but doping density is dependent on the doping method. CISSe films doped by the ACPD method show smaller doping density, the smallest value of carrier concentration is 3.1 × 1017 cm−3 for K-doped CISSe film. All CISSe doped films by ACPD method show higher mobility compared to CISSe film doped by PDT method and larger atom results in higher mobility. The numerical modeling work using SCAPS software showed that solar device with ACPD K-doped CISSe film as absorber layer results in higher efficiency compared to Li, Na- doped and undoped CISSe films.

A new optimization approach for high efficiency of FTO/InS/CIS heterojunction solar cells

ABSTRACT In this work, a new approach is developed to optimize FTO/InS/CIS hetero-junction solar cell using the Slivaco-Atlas software. Each single thin film was prepared by spray pyrolysis method on glass substrates in order to characterize its proper material parameters. Structural and morphological analysis confirmed the deposition of F-doped SnO2, In2S3 and CuInS2 films with porous structures. The extracted physical properties such as thickness, optical, and electrical parameters are considered as input data for Silvaco-Atlas software simulation. It was found that thickness layers and carrier concentration of CIS-based solar cell play an important role in determining solar cell performances. The combination of the optimum parameters enables to obtain the efficiency of 38.20%. The overall investigation on CIS solar cell gives potential suggestions that may lead to the fabrication of the high-efficiency CIS-based solar cell.

Investigation on CuInS2 Films with Wurtzite Structure Prepared from Nitrates

The phases, morphology and band gap of CuInS2 films with wurtzite structure prepared by spin-coating and chemical co-reduction method were studied. Experimental results show that, CuInS2 films with wurtzite structure can be prepared by using nitrates at low temperatures below 220 °C. When the anhydrous ethanol is used as the solvent, CuInS2 film samples prepared with the sulfur powder as the sulfur source, the prepared CuInS2 film has a wurtzite structure with poor crystallinity. When the other solvents such as ethylenediamine and ethanolamine were used, the CuInS2 films prepared by using thiourea as the sulfur source also have the wurtzite structure. The product film with sulfur powder consists of a number of irregular particles with diameters between 0.3 and 0.5 μm, while the product films with thiourea consist of a number of flaky crystals and small spherical particles. The band gaps of the CuInS2 films were estimated by extrapolation method. The estimated band gap of the wurtzite CuInS2 film prepared by sulfur powder as sulfur source is about 1.45 eV, which is close to the theoretical value.

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.

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.

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.

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.

Effect of supporting electrolyte concentration on one-step electrodeposited CuInS2 films for ZnS/CuInS2 solar cell applications

A one-step electrodeposition process was used to obtain CuInS2 (CIS) films on a molybdenum substrate by varying the supporting electrolyte (lithium chloride, LiCl) concentration. The as-deposited samples were characterized by scanning electron microscopy, energy-dispersive spectroscopy, profilometry, and diffuse reflectance spectroscopy. From characterization, it was found that different concentrations of LiCl mainly lead to a morphological change in the obtained CIS films. Moreover, their chemical composition shifted to the stoichiometric composition for high concentrations of the supporting electrolyte. After annealing, the structural analysis from X-ray diffraction revealed that all samples crystallized in the tetragonal phase of CIS. In addition, it was found that the crystallite size increased for samples grown at higher concentrations of LiCl. Optical studies carried out by diffuse reflectance spectroscopy revealed that the band gap values increased from ~ 1.40 to ~ 1.45 eV (average) after the annealing process. Finally, zinc sulfide (ZnS) thin films were chemically deposited onto electrodeposited CIS films in order to evaluate the photovoltaic response of ZnS/CIS bilayer systems. We discovered that ZnS thin films covered the surface of CIS more effectively for the highest concentration of LiCl and that only the ZnS/CIS bilayer with the CIS film obtained at the highest concentration of LiCl showed a photovoltaic response.

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.

An affordable method to produce CuInS2 ‘mechano-targets’ for film deposition

We report on the room temperature, simple and cheap preparation by mechano-synthesis of polycrystalline targets of complex sulphide semiconductors, namely CuInS2 (CIS), to be used for film deposition in physical vacuum techniques such as PLD, sputtering or LT-PED. The sulphur (S)-based targets usually require expensive high pressure equipment to compensate the high S vapour pressure; nevertheless they are indispensable for the deposition of high band-gap semiconductor materials. The comparison of CIS films grown by mechano-synthesis and by commercial targets demonstrates similar material quality, making the mechano-synthesis a viable solution in the fabrication of high band-gap, S-based targets of complex chalcogenides.