Cu2ZnSnS4 Thin Films Research Articles

Studies on Cu2ZnSnS4 (CZTS) powder and thin film prepared from Molecular ink

Abstract Copper Zinc Tin Sulphide (Cu2ZnSnS4) is one of the most promising materials in the field of thin film based solar cell. Nanoparticles and ink form of CZTS prepared by chemical method is well-studied. In the present work CZTS powder made from chemical method and used to prepared films by physical evaporation technique, i.e. flash evaporation. CZTS films were prepared at 200 °C substrate temperature and annealed at 300 °C and 450 °C in vacuum for one hour. The structural, morphological, optical and electrical properties of the as-deposited and annealed were studied. The XRD confirms the wurtzite structure of the CZTS films. Atomic force microscopy indicates that the surface morphology also improves with the annealing. The band gap value of the annealed films is 1.7 eV, implied that the formation of the CZTS material. An electrical measurement signifies the p-type conductivity of the films. As a sum-up, as-deposited films were amorphous, non-uniform and highly resistive, and after annealing all had improve.

A holistic approach to optical characterizations of vacuum deposited Cu2ZnSnS4 thin film coatings for solar absorbing layers

This article aimed at making a good absorber layer of Cu2ZnSnS4 thin film coatings deposited onto glass substrates via spin coating technique with different rotational speeds. Three sets of Cu2ZnSnS4 thin film coatings were prepared at rotations of 3000, 3500, and 4000/min. The thickness of the thin film coatings was measured using a surface profilometer, and the coating thickness shows good rpm dependence i.e., the thickness of the coatings decreased with increasing rpm. The thicknesses of the coatings were in the nanometer (nm) range for all samples. The structural, morphological, and optical properties of the as coated thin films were studied using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), and ultraviolet–visible (UV–Vis) absorption spectroscopy. The XRD pattern confirmed the body-centered tetragonal lattice structure with Kesterite Cu2ZnSnS4 phase having good crystallinity. The average crystallite size increases while lattice strain, dislocation density, and crystallite number are decreased with increasing thicknesses of the Cu2ZnSnS4 coatings. SEM micrographs represent the homogeneous, agglomerated surface without any cracks and pores. The average optical band-gap of the coatings was found to be 1.5 eV. Dielectric parameters such as refractive index, high-frequency dielectric constant, and static dielectric constant were declined with increasing thickness of Cu2ZnSnS4 thin film coatings. These characteristics would allow the Cu2ZnSnS4 thin film coatings to be suitable for an absorber layer used in photovoltaic devices.

Articulating effect of low copper content on structure and optoelectronic properties of spray deposited Cu2ZnSnS4 thin films – From experiment and first-principles investigations

Improvement in the efficiency of truly inexpensive spray-pyrolysed Cu2ZnSnS4 (CZTS) thin film solar cells demands both the minimal presence of secondary phases as well as low carrier concentration. The present work deals with a strategy to obtain high quality spray pyrolysed CZTS films with low carrier concentration by controlling Cu-precursor concentration ([Cu2+]). By reducing [Cu2+] from 0.0136 M to 0.0129 M, film’s microstrain changes from compressive (1.76 × 10−3) to tensile (5.89 × 10−3) in nature, allowing the suppression of secondary phase formation. At an optimally low [Cu2+] of 0.0122 M the film shows pure phase, a lower tensile strain and a free carrier concentration of 3 × 1018 cm−3 with p-type conductivity and a high mobility of 3.22 cm2/Vs. Interfacial charge transfer is also promoted in this condition which is verified from electrochemical impedance spectroscopy. Moreover, the consequence of the modulation in the electrical properties through precursor [Cu2+] on the electronic structure and its optical absorption properties are corroborated from first-principles calculation.

CZTS thin film solar cells on flexible Molybdenum foil by electrodeposition-annealing route

Earth-abundant and non-toxic Kesterite-based Cu2ZnSnS4 (CZTS) thin film solar cells are successfully fabricated on flexible Molybdenum (Mo) foil substrates by an electrodeposition-annealing route. A well-adherent, densely packed, homogeneous, compact, and mirror-like CZT precursor is initially produced through electrodeposition by using a rotating working electrode. Subsequently, the co-electrodeposited CuZnSn (CZT) precursor is sulfurized in quartz tube furnace at 550 °C for 2 h in N2 atmosphere with the presence of elemental sulfur in order to form CZTS. Different characterization techniques like XRD, SEM, HR-TEM, Raman, and Photoluminescence demonstrate that almost phase-pure CZTS formed after sulfurization. A flexible Al/Al-ZnO/i-ZnO/CdS/CZTS/Mo foil solar cell is produced, where CdS is deposited by chemical bath deposition and transparent conducting oxide (TCO) is deposited by DC sputtering. The CZTS solar device shows a 0.55% power conversion efficiency on flexible Mo foil substrate and it constitutes the first prototype of this kind of solar cell produced by electrodeposition-annealing route without any surface modification of the Mo substrate.Graphic abstract

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.

A thin Cu interlayer-mediated control of phase evolution of Cu2ZnSnS4 thin films grown by RF magnetron sputtering of a single elementary target with high white light sensitivity

Although sputter deposition from a single target to prepare Cu2ZnSnS4 (CZTS) thin films appears attractive, it must suppress the growth of secondary phases that detrimentally affect performance of CZTS based thin film solar cells. Here we demonstrate a rational strategy for deposition of phase pure kesterite CZTS films by RF magnetron sputtering using a single target prepared from elemental powders via a thin Cu interlayer-mediated control of phase evolution. The films grown from a target of stoichiometric elemental proportion were Cu poor that determined the reaction pathway during sulfurization and resulted in growth of spurious phases despite a large variation in the sulfurization configuration. Inserting a 195 nm thick Cu interlayer between successively sputtered precursor layers provided improved compositional stability through thermally activated diffusion of Cu from the intermediate layer towards both the sides and resulted in the formation of kesterite CZTS even at a modest sulfurization temperature of 500 °C. The obtained phase-pure films have a bandgap of ~1.58 eV. The films show excellent photoresponse behavior characterized by increase in current by three orders of magnitude at a bias of 3 V upon white light illumination, typically that required for a potential absorber layer in thin film solar cells.

Effect of sulfur powder mass on the formation of MoS2 interface layer between Cu2ZnSnS4 thin film and Mo foil

Cu2ZnSnS4 (CZTS) thin films were fabricated on Mo foil substrates using magnetron sputtering followed by sulfurization. In sulfurization, the solid sulfur powder mass was used to control the formation of MoS2 layer at the CZTS/Mo interface. X-ray diffraction, Raman spectroscopy, and scanning electron microscopy were used for the analyses of crystal phases and morphologies of the samples. The thickness of MoS2 layer and void formation at the CZTS/Mo interface reduced as the sulfur powder mass decreased. However, the reduction of sulfur powder mass reduced the crystallinity of CZTS. No MoS2 layer was found at the CZTS/Mo interface when the sulfur powder mass was 0.5 g. The slopes of linear current-voltage curves of CZTS/Mo structures increased as the sulfur powder mass reduced. Therefore, the interface qualities of CZTS/Mo structures were improved by reducing sulfur powder mass.

Secondary phases and disorder degree investigation of Cu2ZnSnS4 films

In this study, Cu2ZnSnS4 (CZTS) thin films are deposited onto the glass slides via the radio frequency (RF) magnetron sputtering, and subsequently sulfurized at different heating rates of 5 °C/min, 20 °C/min, 35 °C/min and 50 °C/min, respectively. The disorder degrees and the secondary phases of finally obtained CZTS thin films are then systematically investigated by using scanning electron microscopy, X-ray diffraction, energy dispersive X-ray, Raman spectroscopy, Raman mapping, UV–vis–NIR spectroscopy, and the Hall effect measurement system. The morphological, structural, and electrical properties of fabricated CZTS films affected by the heating rate are subsequently evaluated. The heating rate of 20 °C/min during the sulfurization process is found to produce a nearly single-phase kesterite CZTS with a substantially low disorder degree. However, more Cu2-xS and Cu3SnS3 secondary phases are found in samples that are annealed at other heating rates. The effect of heating rate on the decomposition during the sulfurization process is also studied and then elaborated. This study provides an optimal condition for minimizing the secondary phases and disorders, in other words, providing the idea process condition to manufacture the high-quality CZTS thin films for solar cells with high conversion efficiency.

Preparation of Cu₂ZnSnS₄ Thin Films by Successive Ionic Layer Adsorption and Reaction (SILAR) Method for Supercapacitor Applications.

The Cu₂ZnSnS₄ (CZTS) thin films have been prepared at different deposition cycles, deposited on a glass substrate by successive ionic layer adsorption and reaction (SILAR) method followed by the annealing process at elevated temperature. The investigations on the films have been carried out to understand and confirm its structure, functional group present, crystalline morphology, optical and electrochemical behavior. The powder X-ray diffraction patterns recorded indicate that the deposited films are formed in the tetragonal structure. Other parameters like grain size, dislocation density, and microstrain are also calculated. The uniform surface of the films with spherical shaped morphology has been observed by Scanning Electron Microscopy, and the elemental compositions have been confirmed by EDAX. Electrochemical behavior such as cyclic voltammetry, electrochemical impedance spectroscopy and galvanostatic charge-discharge analysis have been carried out by electrochemical workstation. The modified electrode exhibits maximum specific capacitance value as 416 F/g for a pure sample. Optical studies have shown that the band gaps are estimated between 1.40 eV and 1.57 eV.

EFFECT OF TIN PRECURSORS ON THE DEPOSITION OF Cu2ZnSnS4 THIN FILMS

Cu2ZnSnS4 is a potential compound semiconducting material for solar absorber layer in thin film heterojunction solar cells. Chemical spray pyrolysis technique has been successfully employed to deposit these thin films using two different tin precursors. Thin films were characterized by studying their structural, composition, electrical and optical properties. X-ray diffraction pattern reveals that these films exhibit polycrystalline nature with kesterite structure. Lattice parameters of Cu2ZnSnS4 films are found to be a = b = 0.544 nm and c = 1.084 nm. Optical band gap, evaluated from spectral transmittance data, is close to ideal energy gap (1.5 eV) exhibit highest conversion efficiency. Optical absorption coefficient of these films is ≥ 104 cm-1 . These films exhibit p-type nature. A humble attempt is made to fabricate a typical heterojunction Cu2ZnSnS4 thin film solar cell.

The preparation of Cu2ZnSnS4 thin film solar cell based on oxygen containing precursor

In this paper, we reported a new method to fabricate Cu2ZnSnS4 (CZTS) thin film solar cells. Oxygen containing precursor thin films were deposited on the Mo-coated soda lime glass (SLG) by sputtering ZnO, SnO2 and Cu targets. For getting higher quality CZTS thin films, the effects of different annealing temperatures of 380 °C, 480 °C, 580 °C and 650 °C on CZTS films were systematically investigated. The results showed that the optimum annealing temperature was 580 °C. Through optimizing the sulfurization process, phase-pure CZTS thin films with compact and large grains were obtained. Composition analysis showed that O was not detected after sulfurizing process which indicated all of O was replaced by S. And due to the stability of SnO2, the loss of tin can be avoided. In addition, ZnO not only can provide zinc sources, but also can decrease the thickness of MoS2 as a barrier layer. Finally, CZTS solar cells based on sputtering oxides targets were obtained and the preliminary fabricated CZTS thin film solar cells had an efficiency of 5.08%, with an open-circuit voltage of 645 mV, a short-circuit current density of 21.74 mA/cm2 and a fill factor of 36.23%.

Investigation of Zn/Sn ratio for improving the material quality of CZTS thin films with the reduction of Cu2-xS secondary phase

In this study, a sputtering system was adopted for the preparation of Cu2ZnSnS4 (CZTS) thin films with high material quality. The system precisely controlled the elemental ratio in a copper-zinc-tin (CZT) precursor for contributing to the grain growth of CZTS crystallites, and reduced the detrimental formation of the Cu2-xS secondary phase during the high-temperature sulfurization process.The CZT precursor was prepared in a layer sequence of Zn/Sn/Cu/Zn, as the Cu-capping layer could protect the underlying Zn/Sn bilayer from volatilization during the high-temperature sulfurization. The CZT precursors were subjected to the sulfurization process at varied temperatures ranging from 480 to 560 °C for 20 min to form the CZTS thin film. In this study, the Cu/(Zn + Sn) and Zn/Sn ratios in the CZTS film were studied by energy dispersive X-ray spectroscopy measurements, and both ratios revealed elevations with an increasing sulfurization temperature, owing to the thermal volatilization of Zn and Sn. Thus, the formation of the undesirable Cu2-xS secondary phase was enhanced, and the surface roughness and density of voids on the CZTS thin films were increased. For a reduced Zn/Sn ratio with a reduced sulfurization temperature, the improved CZTS thin-film quality was demonstrated by the increased X-ray diffraction (XRD) and Raman intensity, along with the reduction of the XRD linewidth of the (112) CZTS crystal phase. A CZTS thin film with a sulfurization condition of 500 °C for 20 min showed a low Zn/Sn ratio (at 1.1), along with the features of a dense and smooth thin-film surface. Moreover, a reduced photoluminescence spectra full width at half maximum (FWHM) value of 92.7 meV was observed.In addition, for further improving the grain growth of CZTS, a pre-annealing process of a CZT precursor was conducted at a temperature of 350 °C for 30 min. An enhancement of the CZTS crystallite size with the stoichiometric formation of a CZTS phase and a reduced Cu2-XS phase was observed, indicating the superior material quality of the CZTS thin films.

Preparation and photocatalytic properties of Cu2ZnSnS4 for H2 production

Cu2ZnSnS4 (CZTS) thin film photocatalytic water splitting for hydrogen production under visible light irradiation has been reported together with CZTS nanoparticles prepared by ultrasonic spray pyrolysis and hydrothermal method, respectively. CZTS thin film provided higher H2 production rate (68.68 μmol · g−1 · h−1), which was 32 times higher than that of CZTS nanoparticles (2.08 μmol · g−1 · h−1) without loading any noble metals. What’s more, photocatalytic activity of CZTS thin film remained 94% after 48 h which confirmed the good stability and reusability of CZTS thin film. CZTS thin film is a potential and durable candidate for photocatalysis.

Vibrational studies on Cu2ZnSnS4 thin films prepared by single step reactive DC magnetron sputtering

Cu2ZnSnS4 (CZTS) is a potential absorber material among its contemporary contenders for thin film solar cells. Controlling secondary phases in CZTS is a major concern. In the present study, CZTS thin films are prepared by a single step deposition technique: sputtering of individual metal targets of copper, zinc and tin in the sulfide plasma. The control on secondary phase formation and better microstructure properties are realized in the CZTS thin films prepared at low tin-target powers. The vibrational modes investigated by Raman measurement reveal transformation of CZTS thin films from less stable stannite phase to the stable kesterite phase under low Sn-power (30 W and 40 W) conditions.

Cu2ZnSnS4 Thin Film Fabricated by the Calcinated Nanocrystals

AbstractIn the present work, Cu2ZnSnS4 (CZTS) thin film is successfully prepared by the calcinated nanocrystals with screen‐printing approach. The dependences of the obtained samples’ properties on the annealing parameters of temperature and time are well studied via X‐ray diffraction, Raman, field emission scanning electron microscopy, ultraviolet‐visible‐infrared (UV‐vis‐IR) spectroscopy, energy‐dispersive X‐ray spectroscopy, and X‐ray photoelectron spectroscopy treatments. The results suggested that the best performances of prepared sample can be obtained at 600 °C for 20 min. The obtained sample features a kesterite CZTS phase, a surface morphology consisting of microns nanoparticles, a Cu‐rich and Zn‐rich chemical composition, and an ideal band gap of 1.4 eV. Additionally, the impurity phase of copper sulfide resulting from Cu‐rich composition is needed to further improve in the next work.

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.

Atmospheric Modified Thiol-Based Solution Deposition for Cu2ZnSn(S,Se)4 Absorber Layer

Abandoning the traditional deposition of as-prepared Cu2ZnSnS4 (CZTS) thin films in a glove box, a modified thiol-based solution system suitable for deposition in air is described to further reduce device production costs. In this modified approach, metal salts and thiourea are used as the starting materials and are dissolved in a mixed solution of thioglycolic acid and 2-methoxyethanol, forming a homogeneous precursor solution. The as-deposited CZTS thin films are obtained by spin-coating the precursor solution in air, followed by the selenization process to form large-grained Cu2ZnSn(S,Se)4 thin films. Combining the microstructural results with compositional analyses, the optimal selenization conditions for the Cu2ZnSn(S,Se)4 absorber layer were found to be 540°C and 10 min.

Solution processed copper zinc tin sulfide thin films for thermoelectric device applications

In this work, Cu2ZnSnS4 (CZTS) thin film has been fabricated on a soda-lime glass substrate through an economical green chemical route employing nebulizer assisted spray pyrolysis technique. The deposition is carried out under ambient atmospheric pressure without annealing and sulphurization. An investigation was done to reveal the temperature dependence of various characteristics especially the thermoelectric property of this Earth-abundant, nontoxic CZTS films in the range of 300 °C–375 °C. This study reveals the thermoelectric conversion capability of the material in addition to its photovoltaic conversion application. XRD spectra revealed the formation of tetragonal structured kesterite CZTS peaks preferentially oriented along [112] direction. The film thickness and size of the crystallites is found to increase with temperature up to 350 °C while the dislocation density and microstrain decreased. Raman spectra exhibit a phase pure CZTS layer free from secondary and tertiary phases at a substrate temperature of 300 °C whose composition seems to be off stoichiometric with a Cu/(Zn + Sn) ratio of 0.78. The surface morphological analysis shows a dense, smooth and compact surface for the 350 °C sample. The bandgap was found to vary in the range of 1.52–1.74 eV. Refractive index, extinction coefficient and electrical characteristics of the prepared films endorse its usage as an absorber material for thin-film photovoltaic energy conversion. The Seebeck coefficient of 350 °C grown film is found to be 153 μV/K and the corresponding power factor increases to 5.76 × 10−3 W/mK−2 which recommends its utility in the thermoelectric devices.

The choice of Zn or ZnS layer in the stacked precursors for preparation of Cu2ZnSnS4 (CZTS) thin films

Cu2ZnSnS4 (CZTS) thin films are commonly used as an absorber layer in the thin film solar cell structure. In this study, CZTS thin films were produced by sulfurization of stacked precursor films that is prepared by deposition of Cu, Zn, SnS, ZnS films on glass substrate using sputtering method. The sequential sputter deposition was performed to obtain two distinct stacked precursors, Cu/SnS/Zn/Cu and Cu/SnS/ZnS/Cu respectively. Afterwards, annealing process was implemented at various reaction temperatures (500–575 °C) for 1 min utilizing rapid thermal processing (RTP). The EDX measurements revealed that all the prepared CZTS samples had Cu-poor and Zn-rich composition that are non-stoichiometric chemical composition. This non-stoichiometric composition is important for high efficient CZTS based solar cells. XRD measurements revealed that all patterns are dominated by diffraction planes of kesterite CZTS. The CuS, Cu2S and SnS2 secondary phases also were detected in the XRD pattern of some CZTS films. Raman spectroscopy measurements verified formation of kesterite CZTS phase for all films and picked out CTS phase for some samples prepared using Cu/SnS/Zn/Cu precursor films. The surface microstructure of the films that were obtained through SEM displayed polycrystalline surface structure. Room temperature PL emission spectra of the films showed broad peak at around 1.37–1.38 eV, which is near to the optical band gap of kesterite CZTS structure. Electrical characterization of the samples demonstrated that B-525 CZTS thin film has more suitable electrical resistivity and carrier concentration values for CZTS based solar cell applications.

Improved Cu2ZnSnS4 thin film performance via Pb consumption layer

Abstract Adding a certain amount of Pb element into the perovskite solar cells can improve the devices' overall performance. However, there are few reports on the incorporation of Pb into Cu2ZnSnS4(CZTS) thin film solar cells. In this work, a novel absorber layer of CZTS:Pb thin film has been fabricated through sulfurization CZTS precursor with 15 nm Pb layer. XRD, Raman, and EDS characterizations exhibited that Pb was incorporated into CZTS and partially replaced Sn. Meanwhile, XPS measurement indicated that Pb was +4 valence and no distinct change of the CZTS chemical environment. SEM reveals that compact large grains almost span the whole thickness of the absorber when Pb is used as a consumption layer, while some fine grains and voids at the back contact exist in common CZTS films. The best efficiency of CZTS:Pb is 3.01% with the open-circuit voltage of 615.95 mV, the short-circuit current density of 14.74 mA/cm2 and the fill factor of 33.01%, which is mainly due to the Pb consumption layer improving the crystallinity of CZTS.