Properties Of CZTS Thin Films Research Articles

Optical and structural properties of CZTS thin films produced by electrodeposition

Copper-zinc-tin sulfide (Cu2ZnSnS4 or CZTS), a quaternary compound, behaves as an intrinsic p-type semiconductor, making it an attractive, cost-effective and environmentally-friendly alternative as an absorber layer in photovoltaic cells. In this study, we deposited CZTS onto ITO conductive glass substrates using a single-step co-electrodeposition technique known as Cu-Zn-Sn-S (Co-Ed). The deposition process occurred at room temperature in an aqueous citrate electrolyte bath containing copper (II), zinc (II), tin (II), and sulfur. The deposition process was assisted by cyclic voltammetry to study the influence of cycle numbers, in particular 5, 10 and 15, on the structural and optical characteristics of sulfidation-free films. Scans were carried out at a rate of 20 mV/s in the potential range from −1.6 to 0 eV. CZTS thin films were characterized using X-ray diffraction (XRD) and UV–visible spectroscopy (UV–vis). The XRD results indicate the formation of CZTS kesterite, as evidenced by characteristic peaks. Likewise, optical analysis reveals an optical gap energy closely aligned with the optimum gap for the CZTS absorber layer (1.5 eV), making it suitable for photovoltaic applications.

Study of optical and structural properties of CZTS thin films using copper capping layer and sulfurization to correct stoichiometry

Non-toxic, environment friendly and low cost Cu2ZnSnS4 (CZTS) thin films were deposited on sodalime glass substrates by radio frequency magnetron sputter deposition technique. Stoichiometry analysis revealed that the as-deposited films were Cu deficient. Hence, Cu capping layer was deposited, to study its’ effect on optical and structural properties of the films. These films were subsequently sulfurized in a quartz setup. Ultimately, stoichiometric CZTS films with improved Cu content up to 27.4% were obtained. The kesterite CZTS phase was identified in the samples using x-ray diffraction measurements. The morphological studies revealed that, grain size varies as a function of the thickness of Cu capping layer. The formation of undesired Cu2S and ZnS phases were also observed in the film with Cu content above and below the optimum range. Optical bandgap (Eg) of the films could also be optimized by controlling the Cu content in the film. An optimal Cu content between 24% and 26% was found to be appropriate for achieving a desired bandgap within a range of 1.55 to 1.4 eV, suitable for application in thin film solar cells. The CZTS films with corrected stoichiometry have a charge carrier density in the rage of ∼1021 cm−3, which are much better than values reported so far in the literature.

Dependence of CZTS thin film properties and photovoltaic performance on heating rate and sulfurization time

In this study, effect of heating rate and sulfurization time on the properties of CZTS thin films and their photovoltaic performances was investigated. CZTS layers were prepared by a two-stage technique comprising deposition of precursor films by sputtering on Mo-foil substrates (Mo-foil/ZnS/CuSn/Cu) and a sulfurization process utilizing Rapid Thermal Annealing (RTA) approach. Heating rates and sulfurization times at 550 °C were changed to determine the best conditions. CZTS films were characterized by several techniques. All samples showed Cu-poor and Zn-rich chemical composition regardless of the heating rate and annealing time of the sulfurization process. XRD diffraction patterns showed that only kesterite CZTS phase was formed in all samples. Although Raman spectroscopy measurements confirmed formation of kesterite CZTS phase in all samples, forming of Cu2SnS3 (CTS) secondary phase was detected in all films except for the sample prepared utilizing a relatively low heating rate of 1 °C/s and 60 s sulfurization time (CZTS-I-60). The largest crystallite size and the less micro strain and dislocation density were also found in this sample. All CZTS thin films displayed dense and compact polycrystalline surface microstructure. Optical characterizations showed that the optical band gaps of the films were in the range of 1.48–1.58 eV. PL emission spectra of the films exhibited transition from conduction band to acceptor/defect levels instead of band-to-band transition. Solar cells were fabricated and the highest Voc and conversion efficiency (4.39%) were achieved employing the film obtained with ramp rate of 1 °C/s and the sulfurization time of 60 s, because of better structural properties and purer crystal structure determined for this sample.

Tailoring the electrical properties of Cu2ZnSnS4 thin film by heterovalent Al3+ doping

Kesterite Cu2ZnSnS4 (CZTS) thin film is an attractive photovoltaic material. Harmful vacancy and anti-site defects in CZTS can be reduced by equivalent doping. However, equivalent doping leads to a reduction in the carrier concentration that is essential to the built-in electric field and built-in potential of the device. In this work, we propose heterovalent Al doping to provide hole conduction in CZTS thin film. The chemical valence of doping cation Al3+ is different from that of the substituted cation Sn4+. Al-doped CZTS thin films were fabricated by magnetron sputtering and sulfurization. The Al content was controlled by the Al sputtering time of the precursor. The experimental results revealed the successful fabrication of heterovalent Al-doped CZTS with the preferred orientation of the (112) plane. The partial substitution of Sn by Al led to a right shift of the CZTS diffraction peaks. Al doping could improve the crystalline quality of CZTS, reduce the dislocation density and microstrain of CZTS, and enhance the compactness of the thin-film surface. With the increase in Al content, the distance decreased between the Fermi level and the valence band maximum of CZTS, and the hole concentration and conductivity of CZTS increased monotonously while the non-radiative recombination of carriers was suppressed. The conductivity of CZTS reached 1.47 × 102 S/cm. Therefore, heterovalent Al doping was found to be a useful method to regulate the electrical properties of CZTS thin film.

Influence of annealing conditions on the performance of sputtered grown CZTS thin film solar cells

Kesterite Cu2ZnSnS4 (CZTS), with direct and tunable bandgap, high absorption coefficient, low-cost processing, earth-abundance, and non-toxicity, has become a promising absorber material for emerging thin film solar cells. The film growth, phase formation, and stoichiometry, as well as the electrical and optical properties of the sputtered grown CZTS thin films, are greatly influenced by the annealing temperature and pressure. In this work, we use a series of material characterization techniques followed by numerical simulations to determine how the annealing conditions affect the properties of CZTS thin films and the photovoltaic performance of the corresponding thin film solar cells. Sputtered grown CZTS samples were annealed at different temperatures (470 and 560 °C) and pressures (250 and 350 Torr). UV-visible spectroscopy was used to determine the optical bandgap and the absorption spectra. The experimentally determined values are then used as input parameters in the Solar Cell Capacitance Simulator-1 Dimension (SCAPS-1D) simulator tool to determine the solar cell performance. Simulation results show a maximum theoretical power conversion efficiency for the CZTS sample annealed at 560 °C and 350 Torr pressure. The results can lead to the optimization of sputtering conditions for obtaining high quality CZTS films that can yield excellent solar cell performance.

Effect of Al-doping on the thermoelectric properties of CZTS thin film grown by sol-gel method

In this paper, thermoelectric (TE) properties of sol-gel grown Cu2-xAlxZnSnS4 thin films were investigated using Seebeck data. Several thermoelectric parameters such as Seebeck coefficient (71–110 μV/°C), electrical conductivity (29.4–36.98 S/cm) and power factor (1.48 × 10−5- 4.29 × 10−5 Wm−1C−2) were improved with the concentration of Al atoms. The improvement in thermo-electrical properties is linked to the transfer of the electron density to the Cu and Sn atoms, which generated the copper and tin based secondary phases. The formation of secondary phases with the addition of Al atoms in the host CZTS structure is resulted in the simultaneous improvement of Seebeck coefficient and electrical conductivity due to energy filtering effect. Additional measurements such as X-ray Diffraction, Raman Spectroscopy, and Scanning Electron Microscopy were performed to back up this argument. The formation of extra secondary phases with increasing Al atoms concentration was justified by XRD and Raman data. SEM images revealed the irregular formation of grain size having micro and nanoscale.

Impact on Structural, Morphological, and compositional properties of CZTS thin films annealed in different environments

The present study focuses on the impacts of annealing temperature in different ambiances on the morphological behavior and thin-film quality of CZTS nanoparticles. CZTS nanoparticles have been synthesized via the hot-injection colloidal route method. CZTS nanoparticles have been annealed in air, vacuum atmosphere, and sulphur environment (N2 + H2S(5%), respectively at 450 °C for 30 min. The structural, morphological, compositional, and optical properties of all CZTS thin films were analyzed. The volume fraction is increased in the vacuum annealed thin film keeping crystallite size as same as in the as-deposited film. This results in a reduction of cracks and voids and thus the surface defects of the vacuum annealed thin film as confirmed by scanning electron microscope (SEM). AFM also confirms the improved quality of CZTS thin film annealed in a vacuum. PL curves also confirm the minimum defects in the case of vacuum-annealed thin films. Thus, the study reveals that the best quality CZTS thin films i.e. films with the least pinholes, cracks, and voids without any significant change from the initial conditions can be obtained after annealing in the vacuum environment.

Impact of stacking order and annealing temperature on properties of CZTS thin films and solar cell performance

In this study, Cu2ZnSnS4 (CZTS) thin films were synthesized by a two-stage process. In the first stage, CuSn/Zn/Cu (E-type) and CuSn/ZnS/Cu (B-type) stacked films were formed using the sputtering method. In the second stage, precursor films were annealed in sulfur atmosphere utilizing various annealing temperatures (500, 525, 550 and 575 °C) employing the Rapid Thermal Processing (RTP) method. The EDX measurements demonstrated that almost all the samples had Cu-poor and Zn-rich compositions, as targeted. The XRD patterns of all the CZTS samples were dominated by diffraction peaks of the kesterite CZTS phase. In addition to CZTS phase, Cu–S/Sn–S based secondary phases in all E-type CZTS thin films and some B-type CZTS samples annealed at lower temperatures (500 and 525 °C) were observed. The samples annealed at above 525 °C revealed purer crystal structure in terms of secondary phases and they have more promising crystallite size in both types of CZTS thin films. The Raman spectroscopy measurements confirmed the formation of kesterite CZTS phase and distinguished the formation of Cu2SnS3 (CTS) phase for some samples. The samples annealed at 550 °C presented purer structure for potential solar cell application. The SEM surface and cross-section images of all CZTS samples displayed dense and polycrystalline structures but samples annealed at 550 °C presented a larger-grained surface and cross-section structure in both types of CZTS films. PL spectra of the B-type CZTS samples exhibited a purer band structure with respect to E type CZTS samples according to their PL band values. The best solar cell performance was achieved with CZTS thin film prepared using CuSn/ZnS/Cu stack annealed at 550 °C temperature with 252 mV, 32 mA/cm2, and 3.79% parameters.

Impact on Structural and Optical Properties of CZTS Thin Films with Solvents and Ge Incorporation

This report demonstrates nontoxic colloidal nitrate route CZTS (Cu2ZnSnS4) synthesis at room temperature, along with their band grading due to incorporation of Ge as cost of Sn (3%). The parent CZTS, CZGTS (Cu2ZnGeSnS4), and their polyvinyl alcohol (PVA), dimethyl sulfoxide (DMSO) solvent containing solutions doctor blade-coated thin film structural and optical properties are discussed. Their sulfurized thin films thickness have been achieved ±2 μ. It has noticed that addition of Ge in CZTS alloy affects the grain sizes, crystallographic structure, Raman spectral peak shift toward the higher wave number side. The addition of PVA and DMSO is also substantially contributed in their physical property modification by demonstrating the gradual improvement in grain sizes and compactness. Moreover, the gradual changes have also appeared in their X-ray diffractometer (XRD) and Raman spectroscopic results. The optical energy band gaps of the CZTS, CZGTS, and their PVA, DMSO mixed alloyed thin films are obtained in between 1.27 eV to 1.57 eV and 1.58 eV to 1.83 eV.

Influence of thiourea in the precursor solution on the structural, optical and electrical properties of CZTS thin films deposited via spray coating technique

CZTS films were prepared by spray coating using non-aqueous precursor solutions with and without sulphur source and studied their structural, optical and electrical properties. The films prepared by both the routes were sulphurized at different temperatures to study the effect of temperature on the phase formation. Phase purity was confirmed by XRD, Raman analysis and Rietveld refinement technique. The studies revealed proper phase and crystallinity for the films of both routes sulphurized at 550 °C. These films exhibited dense and improved grain structure, optimal bandgap and higher absorption coefficient. The non-thiourea films sulphurized at 550 °C had a carrier concentration of 1.544 × 1019 cm−3, mobility of 0.87 cm2V−1 s−1 and resistivity of 0.46 Ω·cm, while the thiourea films achieved carrier concentration, mobility and resistivity of 3.67 × 1019 cm−3, 0.33 cm2V−1 s−1 and 0.52 Ω·cm, respectively. The comparative study demonstrates that the films under investigation have the potential for the fabrication of efficient solar cells.

Enhancing microstructural and optoelectronic properties of CZTS thin films by post deposition ionic treatment

Kesterite structure Cu2ZnSnS4 (CZTS) was deposited by RF magnetron sputtering, followed by ionic treatment using 0.25 M of NaF and 0.05 M of SnCl2 before being sulphurized. The ionic treatment using sodium and tin improved the structural, morphological, optical, and electrical properties of the CZTS thin films. The added Na and Sn before the sulphurization process promoted the growth of the main peak in (112) direction, indicative of improved crystallinity of the samples. Homogeneously large and smooth grains were also observed. The bandgap was found to be 1.5 eV with a corresponding Urbach energy value of 0.167 meV. The Urbach energy for the treated samples is lower than the untreated, signifying that the treated samples are less disordered and possessed better crystallinity. The carrier concentration was found to have increased by two orders of magnitude to 1.97E+15 cm−3.

Effect of Prefabricated Layer Structure on Properties of CZTS Thin Films and Solar Cells

Cu2ZnSnS4 (CZTS) thin films based on single-layer and double-layer prefabricated layer structure were prepared on substrates by two-step method. The influence of prefabricated layer structure on the surface morphology, element composition and photoelectric properties of CZTS thin film was studied. The crystal structure, surface morphology and composition of the films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS), respectively. The experimental results showed that the CZTS thin film with double-layer prefabricated structure had larger grain size, better crystallization and uniform distribution of film components than the CZTS thin film with single-layer prefabricated structure. The conversion efficiency of CZTS solar cells based on the double-layer prefabricated structure increased from 0.25% of the single-layer prefabricated structure to 3.05%. Therefore, the double-layer prefabricated structure CZTS thin film was more suitable as the absorption layer of CZTS thin film solar cells.

Growth and Characterization of CZTS Thin Films Synthetized by Electrodeposition Method for Photovoltaic Applications

In the present work we deposited CZTS absorber material using a one-step electrodeposition method on ITO glass substrates. We studied the effect of sulfurization temperature on structural, morphological and optical properties of CZTS thin films sulfurized in N2+H2S atmosphere at 350, 375, 400 and 425°C for 10 min respectively for 10 min. The films have been charaterized by different techniques including X-ray diffractometer (XRD), Raman spectroscopy, scanning electron microscopy (SEM) and UV-visible-NIR spectrophotometer. XRD patterns indicated kesterite CZTS with preferential orientation along (112) plane, the intensity of peaks increased with increase of sulfurization temperature signified the amelioration of the crystallinity with sulfurization temperature increased, the estimated crystallite size are in the range of 14.27-37.32 nm. Raman scattering experiments confirmed the presence of CZTS thin films by the characteristic peak at 336 cm−1. SEM images showed the morphology of CZTS thin films improved with increasing of sulfurization temperature. UV-Visible-NIR spectrophotometer showed that the values of optical absorption coefficient are larger than 104 cm−1 and optical band gap energy of CZTS thin films decreased with increasing of sulfurization temperature ranging 1.56 and 1.66 eV. These results make the electrodeposited CZTS films a suitable material as absorber material in solar cells applications based thin films.

Impact of sulfurization parameters on properties of CZTS thin films grown using quaternary target

In this study, CZTS thin films were grown by annealing of sputtered films using quaternary single target employing various annealing parameters. The effects of the post-sulfurization treatment, reaction temperature (500, 525, 550 and 575 °C) and sulfurization time (60, 90, 120 and 150 s) on the properties of CZTS thin films were analyzed. The optimization of reaction temperature for 60 s dwell time was examined by annealing the precursor films with/without sulfur atmosphere. It was shown that annealing of the films under the sulfur atmosphere prevents Zn-loss in the samples for higher annealing temperatures (550 and 575 °C) and hindering the formation of secondary phases such as Cu2−xS, Cu2SnS3 (CTS). The FWHM values of the sulfurized samples revealed that the sulfurization temperature of 550 °C is preferable for the fabrication of CZTS samples. Further optimization was performed at 550 °C for various sulfurization times. It was seen that all the samples have Cu-poor and Zn-rich composition. The XRD pattern of CZTS samples displayed formation of kesterite CZTS phase but SnS2 phase formations were also observed for longer sulfurization time (> 120 s). It was also observed that the sulfurization time has more significant contribution on the crystallite size of the samples with respect to sulfurization temperature. The Raman spectra of the CZTS samples confirmed the formation of kesterite structures for all the films and appearance of secondary phase for films prepared using longer sulfurization time (> 120 s). All the samples displayed a dense and polycrystalline surface morphology, but the sulfurized sample for 120 s displayed more homogenous and prominent morphology. The room temperature PL measurements demonstrated a broad band which peaked at about 1.36–1.37 eV, which is very close to the band gap of kesterite CZTS structure. The electrical characterization of the samples showed that all the samples have p-type conductivity and the CZTS-S-550-120 sample has a more promising result considering both resistivity and carrier concentration.

Effect of annealing under different atmospheres of CZTS thin films as absorber layer for solar cell application

The influence of annealing under several atmospheres on the structural and optical properties of Cu2ZnSnS4 (CZTS) thin films was investigated. Thin films were deposited on ordinary glass substrates by vacuum thermal evaporation method. In order to optimize the growth of CZTS films, the samples were annealed under different atmospheres: vacuum, nitrogen (N2), Sulfur (S2) and under vacuum followed by sulfuration. The structural study of CZTS films was carried out using the X-ray diffraction. The spectra indicated the improvement of the crystalline quality of CZTS films after the thermal treatments. All annealed films exhibited a preferential orientation along the (112) plane. The optoelectronic properties of CZTS thin films were investigated using UV–Visible spectrophotometry. The optical study of annealed samples revealed a high absorption coefficient that exceeded 104 cm−1 and a band gap in the range of 1.48–1.56 eV.

Fabrication of high-quality kesterite Cu2ZnSnS4 thin films deposited by an optimized sol–gel sulphurization technique for solar cells

Kesterite Cu2ZnSnS4 (CZTS) thin films were prepared by spin-coating deposition of sol–gel precursor followed by optimized sulphurization via custom-made home-built sulphurization setup. The effects of sulphurization on the structural, morphological, optical and electrical properties of CZTS thin films were investigated. X-ray diffraction and Raman spectroscopy studies revealed that the sulphurized CZTS thin films have a polycrystalline nature with a kesterite phase and the crystallite size of sulphurized CZTS thin film is higher as compare to as-synthesized CZTS thin films. The direct optical bandgap of sulphurized CZTS thin film is found to be 1.5 eV. Hall measurement indicates that the sulphurized CZTS thin films have p-type conductivity with charge carrier concentration of 9.47 × 1019 cm−3. Finally, a thin film solar cell was fabricated with the configuration—SLG/FTO/CdS/CZTS/Al. A photoelectric conversion efficiency of 1.5% was achieved with an open-circuit voltage of 0.32 V and a short-circuit current density of 11.9 mA cm−2. These findings clearly show that quality of CZTS samples and photovoltaic performance could be effectively improved by an optimized sol–gel sulphurization process.

Effect of Annealing Temperature on Morphology and Optoelectronics Properties of Spin-Coated CZTS Thin Films

The effect of different annealing temperatures (300, 400, 500 and 550 °C) on the crystallinity, morphology, linear and particularly the nonlinear optical properties of CZTS thin films that were deposited on glass substrate employing a sol–gel spin-coating method was investigated in this work. The obtained results for X-ray diffraction (XRD) indicate a polycrystalline structure of CZTS thin film, the scanning electron microscopy (SEM) and atomic force microscopy (AFM) micrographs showed a uniform and dense texture of the samples, besides the effect of annealing temperatures on CTZS morphology and surface was discussed. Linear optical properties of CZTS thin films were performed by UV–Vis spectrophotometer, both band-gap energy and absorption coefficient were determined and extracted from the variation of the optical transmission and absorption with the wavelength, Eg of the films annealed at 300, 500 and 550 °C was found to be 1.58 eV against 1.63 eV for the film annealed at 400 °C. However, the optical nonlinearity characterizations of CZTS films examined by third harmonic generation (THG) technique exhibited an interesting nonlinear optical responses between 1.10 × 10–20 and 1.84 × 10–20 m2 V−2 which can enlarge the application field of the studied material.

Effect of Cu and Sn concentration on the performance of all-sprayed CZTS solar cell

Cu2ZnSnS4/In2S3 thin film solar cell was prepared using chemical spray pyrolysis. Influence of variation in copper concentration in precursor solution on the properties of CZTS thin films was monitored. Concentration of copper was found to have essential role in adjusting composition and crystallinity of CZTS thin films. Junction was fabricated using CZTS as absorber layer and spray pyrolysed In2S3 as buffer layer. Two sets of devices were prepared, one by varying copper concentration and the other by varying tin concentration in the precursor solution for the deposition of CZTS thin films. For both sets, In2S3 thin films were deposited as buffer layer and Ag electrodes were used for taking contacts. All the performance parameters were found to have dependence on the concentration of Cu and Sn. For getting maximum conversion efficiency, the sprayed CZTS absorber layer should have elemental ratio of Cu:Zn:Sn:S=2.5:1:0.7:12 in the precursor solution. Maximum efficiency obtained was 1.85 %.

Effect of tin concentration on the structural, optical and thermoelectric properties of CZTS thin films gown by chemical solution method

In this work, we have modulated the structural, morphological, optical and thermoelectric properties of CZTS thin films (TFs) by controlling the concentration of tin atoms. The CZTS TFs were grown by simple chemical solution method by changing tin mole concentration from 0.5 mM to 2.0 mM (labeled as T1, T2, T3 and T4). XRD data have revealed the formation of best crystalline CZTS TF at 1.5 mM tin concentration because tin (Sn+4) atoms are placed its own lattice sites therefore achieved the best crystal quality of CZTS. Furthermore, the phase purity of CZTS TF was confirmed by Raman spectroscopy. The lattice vibration of CZTS TF were observed at 329 and 334 cm−1 with A1g mode and 367 cm−1 with B(TO) mode. The strongest Raman CZTS vibrational mode was observed for sample T3 which supported our XRD data. SEM images demonstrated that the surface of grown CZTS thin films became smoother with increasing the mole concentration of tin atoms up to 1.5 mM because the density of CuS grains has minimum value for this sample. The optimum band gap of T1, T2, T3 and T4 samples was estimated to 2.23, 2.15, 1.91 and 1.82 eV respectively which also confirmed that sample T3 has band gap value very close to reported value. The Seebeck coefficient, electrical conductivity and power factor values were enhanced from (243–762 μV/°C), (21–152 S/cm) and (1.24 × 10−4- 8.82 × 10−2Wm−1K−2) with increasing the mole concentration of tin (0.5–1.5 mM) at measurement temperature 100 °C.

Modulation of structural, optical and thermoelectric properties of sol-gel grown CZTS thin films by controlling the concentration of zinc

Abstract In this manuscript, we have demonstrated the effect of Zinc concentration on the structural, optical and thermoelectric properties of CZTS thin films (TFs) grown by sol-gel technique. We have deliberately changed the mole concentration of zinc from 0.5 to 2.0 mM (labeled as Z1, Z2, Z3 and Z4 respectively) to modulate the various properties. The XRD data demonstrated that Z2 sample with Zn concentration 1.0 mM has better structure with minimum number of secondary phases as compared to other samples because extra Zn atoms may create stress in the CZTS lattice. Raman spectroscopy measurements demonstrated that A1 mode of CZTS phases was observed at 334 cm−1 along with the presence of binary and ternary phases of Sulfide. It was also observed that Z2 sample has the strongest A1 Raman mode. The surface morphology of grown samples was observed using scanning electron microscope. The SEM images suggested that increasing Zinc concentration causes the surface rough. UV/Vis and photoluminescence spectroscopy results confirmed that sample Z2 has optimum value of band gap whereas Z1, Z3 and Z4 have band gap values deviated from experimentally reported value. Seebeck data depicts that sample Z2 has the lowest value of Seebeck coefficient. It may be explained as; Seebeck coefficient is strongly dependent upon the secondary phases and Z2 has minimum number of secondary phases, therefore lowest value is understandable.