CuInS2 Thin Films Research Articles

Fabrication of a CuInS2photoelectrode using a single-step electrodeposition with controlled calcination atmosphere

n-type CuInS2 thin films were fabricated by a one-step electrodeposition of Cu/In/S precursors on a transparent fluorine-doped tin oxide (FTO) substrate followed by calcination in a mixture of N2 and H2 at 500 °C without the need of toxic H2S gas for sulfurization. The analyses of structural and optical properties revealed that tetragonal chalcopyrite CuInS2 thin films were obtained when heat treated in a mixture of 8% H2 and 92% N2; whereas calcination in pure N2 resulted in the formation of CuInS2 with a considerable amount of In2O3 and CuxS impurities. The synthesized n-CuInS2 thin film has an optical bandgap of 1.3 eV with the conduction band at ca. −1.2 V vs. Ag/AgCl at pH 6.5. The heat treatment in a mixture of H2 and N2 provided a reducing atmosphere to suppress the oxide formation of the electrodeposited Cu/In/S elements. It also increased the donor density of CuInS2 sixfold by increasing the density of the sulfur vacancies (known to be electron donors) at the grain surface. As a result of the improved purity and increased donor density, the hydrogen treated CuInS2 thin film yielded a photocurrent density of ∼8 mA cm−2 at 0.5 V vs. Ag/AgCl in 0.25 M Na2S and 0.35 M Na2SO3 under visible light illumination, which is a fourfold enhancement as compared to that obtained from the CuInS2 film calcined in pure N2.

The Effect of Thickness on Optical Band Gap and N-type Conductivity of CuInS2 Thin Films Annealed in Air Atmosphere

Structural, electrical and optical properties of CuInS2 thin films of various thicknesses, grown on heated glass substrates at 100°C by thermal evaporation method were studied. These films were annealed in air atmosphere at temperature of 200°C. The thickness of the CIS films was varied from 436 to 80nm. It was found that the structural properties, FWHM and grain size degraded with decreasing its thickness. The peak intensity decreases with the film thickness and the X-ray spectra are polycrystalline in nature excluding films with thickness less than 111nm, the peak intensity disappears and films are amorphous in nature. However, with decreasing the film thickness from 436 to 111nm, the optical band (Eg) gap of CuInS2 material is in the range 1.42 to 1.81eV. Hot probe method showed that all the annealed CuInS2 samples exhibit n-type conductivity with low resistivity values in the range 3.60 to 0.08 kΩ.m. We suggests that the minimum thickness to obtain polycrystalline CuInS2 thin films is 111nm, the band gap energy of CuInS2 thin films can be controlled by varying the film thickness and the n-type conductivity can be obtained after annealing in air atmosphere.

Effects of sulfurization and Cu/In ratio on the performance of the CuInS2solar cell

Photovoltaic CuInS2 (CIS) thin films were prepared from thermally evaporated Cu/In precursors, having various Cu/In ratios, under different sulfurization conditions. The sulfurization was carried out in a quartz tube furnace under a steady or flowing H2S/Ar gas mixture at various temperatures ranging from 450 to 550 °C. The effects of the Cu/In ratio and sulfurization condition on the grain size, surface morphology, surface roughness, microstructure and defect formation of the resulting CIS films were examined. It was found that the effects depend on the processing conditions. Particularly, we show that sub-bandgap generated defects can be inferred by photoluminescence data. Selected CIS thin films were used as absorber layers for the fabrication of thin film solar cells. The best solar cell efficiency of 6.29% was obtained from the 500 °C-sulfurized absorber layer having a Cu/In ratio of 1.8. Effect of absorber layer characteristics on the cell efficiency was also discussed. Copyright © 2013 John Wiley & Sons, Ltd.

Solvothermal synthesis of CuInS2 powders and CuInS2 thin films for solar cell application

In this study, a facile solvothermal method was developed to prepare CuInS2 powders and CuInS2 thin films. The CuInS2 powders and CuInS2 thin films were prepared by solvothermal route using the precursor of Copper (II) chloride, indium (III) nitrate, thiourea, oxalic acid, hexadecyl trimethyl ammonium bromide and ethanol. The morphology, crystallographic structure, chemical composition and optical band gap of CuInS2 powders and CuInS2 thin films were investigated using scanning electronic microscope (SEM), X-ray diffraction (XRD), energy dispersive spectrometry (EDS) and UV–vis spectroscopy. The results reveal that both CuInS2 powders and CuInS2 thin films are in chalcopyrite phase. The CuInS2 powders are mainly composed of flower-like microspheres. Both microstructure of the sphere surface and diameter of sphere are affected by indium nitrate concentration in precursors. The CuInS2 thin films are composed of a large number of uniform flower-like nanosheets, and the nanosheets become smaller in size and denser in distribution density with increasing concentration of thiourea. The optical band gap is found to be 1.44 and 1.52 eV for CuInS2 powders and CuInS2 thin films, respectively. The deposition mechanism of the CuInS2 is discussed.

Crystal Quality Improvement of CuInS<sub>2</sub> Thin Film by Two Step Fabrication Method with Bismuth Addition

CuInS2 (CIS) is the promising candidate of an absorber layer of high efficiency thin film solar cells. The crystal quality of CIS is one of the important factors for high efficiency. A chemical doping approach using antimony and bismuth (Bi) is well known for improving crystal quality in Cu (In,Ga)Se2 thin films. In this study, the effect of Bi doping on evaporated CIS thin films was investigated. A CIS thin film without Bi doping annealed at 600°C showed small crystal grain size of ~1 μm, which was smaller than the CIS film thickness of 2 μm. The small addition of 50 nm-thick Bi promoted crystal growth and large grain size of greater than 1 μm, which was comparable to the CIS film thickness, was realized. The CIS films without and with Bi addition had surface precipitates identified as Cu-S and Cu-Bi-S compounds, respectively. The crystal growth promotion by Bi addition can be attributed to that the Cu-Bi-S compound which has lower melting point of 470~490°C than that of the Cu-S compound of 507°C acted as flux for crystal growth.

Synthesis and characteristics of spray deposited CuInS2 nanocrystals thin films for photovoltaic applications

Nanocrystalline thin films of CuInS2, an attractive absorber material for highly efficient and terrestrial photovoltaic devices, were deposited on ultraclean glass substrates using spray pyrolysis technique. The prepared films were characterized by FESEM, FETEM, HRTEM, AFM, XRD, optical absorption spectroscopy, photoluminescence and current–voltage characteristics. The films exhibit almost smooth, dense and uniform topography; and have nano-sized particles 40–60nm of CuInS2. XRD data show that the films are polycrystalline and have chalcopyrite (tetragonal) structure with crystallite size 45–60nm. Optical absorption studies show that the band gap of spray deposited CuInS2 films is 1.55eV, while absorption coefficient is of ∼105cm−1. PL spectra have only one peak at 1.43eV which may be attributed to the excitonic recombination through donor–acceptor impurity levels in the sample. Furthermore, CdS/CuInS2 heterojunction was also produced onto ITO coated glass substrate to evaluate solar cell parameters such as short circuit current density, open circuit voltage, fill factor and conversion efficiency.

Studies in CuInS2 based solar cells, including ZnS and In2S3 buffer layers

The influence of the growth conditions on the surface chemistry and on the homogeneity of the chemical composition of CuInS2 (CIS) thin films, prepared by sequential evaporation of metallic precursors in presence of elemental sulfur in a two-stage process, was studied by X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). It was found that the growth temperature affects the phase in which this compound grows. The samples deposited at temperatures around 500°C (2nd stage) contain mainly the CuInS2 phase; however, secondary phases like In2S3, Cu2S were additionally identified at the surface and in the bulk of CuInS2 samples deposited at temperatures greater than 550°C. Also, the elemental composition of the layers constituting the Glass/Mo/CuInS2/buffer/ZnO structure was studied through Auger electron spectroscopy (AES) depth profile measurements. AES measurements carried out across the Glass/Mo/CuInS2/buffer/ZnO heterojunction gave evidence of Cu diffusion from the CuInS2 layer towards the rest of the layers constituting the device, and of the formation of a MoS2 layer in the Mo/CuInS2 interface. The performance of CuInS2-based solar cells fabricated using CBD (chemical bath deposition) deposited ZnS as buffer layer was compared to that of cells fabricated using CBD deposited In2S3 as buffer.

Influence of annealing temperature on the phase composition and optical properties of CuInS2 films

We studied the growth of CuInS2 thin films by single-source evaporation of CuInS2 powder in a high-vacuum system with a base pressure of 10−3Pa. After evaporation, the films were annealed in a sulfur atmosphere at temperatures from 200 to 500°C for 1h. XRD curves and Raman spectra of the films demonstrated that chalcopyrite CuInS2 was the major crystalline phase. The morphology of CuxS exhibited a star-like structure, which we report for the first time. The phase composition and optical properties of our polycrystalline thin films were effectively modified by annealing in S. For films annealed at 200 and 350°C, a secondary CuIn11S17 phase appeared, which may be related to solid-state reaction in the S atmosphere. This secondary CuIn11S17 phase has not been widely reported in previous studies. After annealing at 500°C, only a chalcopyrite phase was detected, with bandgap energy of 1.46eV, which is nearly identical to the optimal bandgap energy (1.5eV) of single-crystal CuInS2. This indicates that the composition of the CuInS2 film annealed at 500°C was nearly stoichiometric. The bandgap of the samples first increased and then decreased with increasing annealing temperature, which may be attributed to an increase in grain size, the secondary CuIn11S17 phase, and deviation from stoichiometry.

Preparation and characterization of cost effective spray pyrolyzed absorber layer for thin film solar cells

In this study, highly (112) oriented crystalline copper indium disulfide (CuInS2) thin films with high mobility have been deposited via ultrasonic spray pyrolysis. Structural and electrical properties of CuInS2 thin films were examined to utilize them in solar cell applications. Various amounts of precursor solution ranging from 0.25 to 2.02ml/cm2 were used to form CuInS2 thin films onto the soda lime glass substrates. Scanning electron microscopy (SEM) analysis revealed that all sprayed films were pin-hole and crack free. Atomic percent ratios of the Cu/In and S/In were very close to the targeted stoichiometric ratios of 1/1 and 2/1, respectively. X-ray diffraction (XRD) studies revealed that all the deposited films were polycrystalline and exhibiting the chalcopyrite structure. Optical band gap energy of the films were calculated as 2.85eV and decreased to 1.40eV by increasing the solution loading. Hopping mechanism could be considered as the dominant conduction mechanism in the studied temperature range. Carrier concentrations in CuInS2 films were ranging between 1015 and 1017cm−3. Mobility and the carrier concentration of the CuInS2 thin films deposited from 1.52ml/cm2 solution loading were 40.1cm2/Vs and 1.69×1017, respectively. At last but not least, the amount of solution used in this study to form CuInS2 thin films was one of the lowest values reported in the literature.

Fabrication of CuInS2 thin film by electrodeposition of Cu–In alloy

CuInS2 thin films of chalcopyrite structure were fabricated on indium tin oxide substrates by electrochemical co-deposition of copper–indium alloy layers at 1 atm, followed by sulphurization. Co-deposition potential was determined according to voltammetric study. The effect of deposition potential, concentration of complexing agent, and heat treatment temperature on the morphology and crystal structure of the obtained thin films was examined. Then the influence of heat treatment on the optical and photoelectrochemical performance of CuInS2 thin films was studied. In the electrodeposition solution containing 5 mM CuCl2, 5 mM InCl3 and 0.2 M triethanolamine at pH of 4.0, Cu2In alloy layers were observed at the deposition potential of −1000 mV (vs. saturated calomel electrode). After sulfurization, chalcopyrite CuInS1.5 thin films with the impurity elements of C and O were obtained. Those thin films exhibited p-type semiconductor behavior with the bandgap of about 1.5 eV. The conversion efficiency can be improved further by depositing PbS particles on the thin films.

Binder-Free Cu–In Alloy Nanoparticles Precursor and Their Phase Transformation to Chalcogenides for Solar Cell Applications

A low-cost, nonvacuum fabrication route for CuInSe2 and CuInS2 thin films is presented. To produce these films, binder-free colloidal precursors were prepared using Cu–In intermetallic nanoparticles that were synthesized via a chemical reduction method. The Cu–In alloy precursor films were transformed to CuInSe2 and CuInS2 by reactive annealing in chalcogen-containing atmospheres at atmospheric pressure. The as-synthesized nanoparticles and the annealed films were characterized by X-ray diffraction, transmission electron microscopy, scanning electron microscopy, energy dispersive X-ray spectrometry, electron probe X-ray microanalysis, Raman spectroscopy, and Auger electron spectroscopy depth profile measurements to elucidate the phase evolution pathway and the densification mechanism of the Cu–In–Se–S system. Solar cell devices made with CuInSe2 and CuInS2 absorbing layers exhibited power conversion efficiencies of 3.92% and 2.28%, respectively. A comparison of the devices suggested that the microstructur...

Synthesis and characterization of sprayed Zn-doped polycrystalline CuInS2 thin films

Copper indium disulphide (CuInS2) is an efficient absorber material for photovoltaic applications. In this work Zn (0.02 and 0.03M) doped CuInS2 thin films are (Cu/In=1.25) deposited onto glass substrates in the temperature range 300–400°C. XRD patterns depict, Zn-doping facilitates the growth of CuInS2 thin films along (112) preferred plane and other characteristic planes. Optical studies show, 90% of light transmission occurs in the IR regions; hence Zn-doped CuInS2 can be used as an IR transmitter. The absorption coefficient in the UV–vis region is found to be in the order of 104–105cm−1. Optical band gap energies increase with increase of temperatures (0.02M – (1.93–2.05eV) and 0.03M – (1.94–2.04eV)). Well defined, broad Blue and Green band emissions are exhibited. Resistivity study reveals the deposited films exhibit semiconducting nature. Zn species can be used as a donor and acceptor impurity in CuInS2 films to fabricate efficient solar cells and photovoltaic devices.

Influence of vacuum annealing on the properties of SILAR CuInS2 thin films and optimization of annealing duration

The structural, compositional, morphological and optical properties of as-deposited and vacuum annealed CuInS2 thin films prepared by successive ionic layer adsorption and reaction method are studied by X-ray diffractometer, energy dispersive X-ray analyzer, scanning electron microscope and spectrophotometer respectively. The influence of vacuum annealing on the properties of CuInS2 (CIS) thin films is discussed, annealing duration has also been optimized and reported in this paper.

Electrodeposition and Properties of CuInS<sub>2</sub> Thin Films

The preparation and characterization of CuInS2 thin films on ITO glass substrates prepared by one-step electrodeposition have been reported. Samples were characterized using X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDX) and scanning electron microscopy (SEM). The results indicate that CuInS2 is the major phase for the film deposited at -1.0 V, after annealing at 550°C in sulfur atmosphere, and the sample is Cu-rich and p-type semiconductor. Additionally, the energy band gap and carrier concentration for the sample were found to be 1.43 eV and 4.20×1017 cm−3, respectively. Furthermore, the maximum photocurrent density of the sample was found to be -1.15 mA/cm2 under 255 lx illumination, the sample shows the photo-enhancement effect.

Thermal behaviour of precursors for CuInS2 thin films deposited by spray pyrolysis

The thermal decomposition of precursors for copper indium disulphide (CuInS2) thin films obtained by drying aqueous solutions of copper chloride (CuCl2), indium chloride (InCl3) and thiourea (SC(NH2)2) at the Cu:In:S molar ratios of 1:1:3 (1) and 1:1:6 (2) was monitored by simultaneous thermogravimetry /differential thermal analysis/ evolved gas analysis-mass spectrometry (TG/DTA/EGA-MS) measurements in a dynamic 80 %Ar + 20 %O2 atmosphere. X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy were used to characterise the dried precursors and products of the thermal decomposition. The precursors 1 and 2 are mixtures of copper and indium chloride thiourea complex compounds, whilst 1 can also contain unreacted InCl3. The thermal degradation of 1 and 2 in the temperature range of 30–800 °C consists of six steps with a total mass loss of 71.5 and 89.8 %, respectively. According to XRD, CuInS2 is formed below 300 °C. Decomposition of 1 and 2 is completed at 620 and 600 °C, respectively. The final decomposition product of 1 at 800 °C consists of a mixture of In2O3 and CuO phases, whilst 2 consists of In2O3, CuO and Cu2In2O5 phases. EGA by MS revealed the release of CS2, NH3, H2NCN and HNCS, which upon their oxidation also yield COS, SO2, HCN and CO2.

Optimization of deposition temperature of SILAR Cu-rich CuInS2 thin films

CuInS2 (CIS) is studied widely as a promising absorber material for high efficient and low cost thin film solar cells. CIS thin films are prepared on soda lime glass substrates using Successive Ionic Layer Adsorption and Reaction (SILAR) technique at different deposition temperatures (40 to 70 °C). The structural, compositional and optical properties are studied with x-ray diffractometer, energy dispersive x-ray analyzer and spectrophotometer. The influence of the deposition temperature on the properties of CIS thin films is discussed in this paper in detail.

Preparation of CuInS2 thin films by paste coating

Precursor pastes were obtained by milling In2S3 and CuS. CuInS2 thin films were successfully prepared by precursor layers, which were coated on glasses and Mo foils substrates using these pastes, and were annealed in a N2 atmosphere. The annealed films were characterized by XRD, scanning electron microscopy (SEM) and UV–vis spectrophotometry. The results indicate that chalcopyrite CuInS2 is formed at 200 °C and the crystallinity of this phase is improved as the temperature rises. The compression of precursor layers before annealing step is one of the most essential factors for the preparation of perfect CuInS2 thin films. The UV–vis spectroscopy shows that the observed band gaps of the CuInS2 films increase from 1.21 to 1.45 eV corresponding to the Cu/In ratios.

Study on the effects of different sulfur vaporization temperature on the properties of CuInS2 thin films

CuInS2 (CIS) absorber thin films were prepared by sulfurization of In/Cu metallic stacked precursor. The precursor thin films were sulfurized using a commercial furnace system in the S2 (s)+Ar atmosphere at 425°C for 1h. Effects of different S vapor temperature from 150 to 400°C on the structural, morphological, compositional and optical properties of CIS thin films were investigated. X-ray diffraction and Raman studies showed that the sulfurized thin films with S vaporization temperature below 300°C exhibited CIS tetragonal structure with secondary phases such as CuxSy, CuIn5S8, and InxSy. The sulfurized thin films with S vaporization temperature over 350°C showed a single CIS tetragonal structure. Compositional ratio of CIS thin films showed that Cu/In and S/(Cu+In) ratio in the CIS thin films with S vaporization temperature over 350°C were 1.0–1.2 and 0.9–1.1, respectively, while compositional ratio deviated from stoichiometry when the sulfurized thin films below S vaporization temperature of 350°C. Optical study showed that the band gap energy and the absorption coefficient of CIS thin films were estimated from 1.18eV to 1.5eV and over 104cm−1, respectively.

Preparation of monodispersed CuInS2 nanopompons and nanoflake films and application in dye-sensitized solar cells

Monodispersed nanopompons and thin films of CuInS2 with hierarchical nanostructure are obtained via a solvothermal method. The hierarchical thin film of CuInS2 has been reported for the first time to display excellent catalytic activity as a counter electrode in dye-sensitized solar cells, and a power conversion efficiency of 4.8% is achieved.

Fabrication of CuInS2 and Cu(In,Ga)S2 thin films by a facile spray pyrolysis and their photovoltaic and photoelectrochemical properties

Polycrystalline CuInS2 chalcopyrite thin films were formed on a Mo-coated glass substrate by annealing of spray deposited precursor films in a sulfur atmosphere. Structural and photoelectrochemical analyses of CuInS2 films obtained by annealing at 500 °C and 600 °C revealed that a well-defined crystalline film was obtained by the 600 °C annealing. Owing to these favorable properties, the solar cell with an Al:ZnO/CdS/CIS/Mo/glass structure based on the 600 °C annealed CuInS2 film showed higher conversion efficiency than that obtained on the cell derived from the 500 °C annealed CuInS2. Partial incorporation of Ga in the CuInS2 film with a Ga/In ratio of ca. 0.2 to form a Cu(In,Ga)S2 mixed crystal without any reduction of photoelectrochemical properties can be achieved by introduction of a Ga source in the sprayed solution. As a result, the solar cell based on the 600 °C annealed Cu(In,Ga)S2 film showed the best conversion efficiency (5.8%) of the present sprayed chalcopyrite films. By introduction of a CdS thin layer followed by loading Pt deposits, moreover, the 600 °C annealed Cu(In,Ga)S2 film worked as a photocathode for photoelectrochemical water splitting with applied bias potential of >0.65 V.