CZTS Phase Research Articles

Influence of electrodeposited Cu2ZnSnS4 films for the reduction of 4-nitrophenol through electronic relay approach and serve as photoelectrode in PEC device

We explore the possibility of thin film Cu2ZnSnS4 (CZTS) as an effective catalyst for the reduction of 4-nitrophenol to 4-aminophenol in presence of NaBH4 through electronic relay process with the rate constant of 0.20 min−1, also as photoelectrode material for low-cost photoelectrochemical solar cells. Cu2ZnSnS4 thin films with thickness of ∼ 2 μm have been synthesized by an electrochemical approach. The electrochemical bath contained an aqueous solution of Cu(NO3)2·3H2O, Zn(NO3)2.6H₂O, SnC2O4 and Na2S2O3 with Citric acid as a chelating ligand at an optimum pH∼3.65. The morphology, composition, and optical properties were characterized by XRD, FE-SEM, HR-TEM, UV–Vis, FT-IR, and EPR analysis. The growth kinetics of CZTS have been invested with different time intervals, also changes of band gaps of deposited material have been noticed. Cyclic voltammetry of the electrode is done to predict the co-deposited system in the quaternary semiconductor in 0.1 M KCl as supporting electrolyte. The deposited Kesterite phase of CZTS has been systematically investigated to serve as an effective counter electrode material for photoelectrochemical (PEC) energy conversion in 0.5 M polysulfide (Na2Sx) redox couple which showed an efficiency of ∼ 4.395 %. The development of a facile and green chemical route for the preparation of a well crystallized and stable CZTS photoelectrode still remains a challenge.

Prospects of buffer layer optimization for electrodeposited CZTS-based thin-film solar cell using SCAPS-1D

Kesterite Cu2ZnSnS4 (CZTS) has recently attracted the intensive attention of researchers as a significant photovoltaic material for the scalable production of thin film solar cells. We have particularly focused on replacing the conventional CdS buffer layer with non-toxic and earth-abundant materials of zinc stannate (Zn2SnO[Formula: see text] in environmentally friendly thin-film solar cells based on CZTS. Zinc stannate (ZTO) with a wide bandgap energy of about 3.33[Formula: see text]eV can be a promising material to reduce photon absorption loss and improve the photovoltaic performance of the device. Thus, the absorber and buffer layers were practically prepared to determine the bandgaps of layers for citation in SCAPS-1D simulation program. We employed chemical methods to deposit the CdS and CZTS layers and succeeded to obtain a high-quality kesterite phase of CZTS. The common configuration of FTO/CZTS/buffer/ZnO/AZO was the basis of the simulations in which, the thicknesses of the absorber and buffer layers were optimized by using the SCAPS-1D. According to the outcome of the simulations, the ZTO buffer layer has a better performance than CdS.

Fabrication of CZTS Thin Film on Flexible Cu-Foil Substrate by Two-Stage Process

In this research, CZTS thin films grown on flexible Cu-foil with varying sulfurization times. Various characterization methods were employed, including X-ray diffraction (XRD), Raman spectroscopy, energy-dispersive X-ray spectroscopy (EDX), scanning electron microscopy (SEM), optical transmission, and photoluminescence (PL) measurements. Distinctive diffraction peaks characteristic of the kesterite CZTS phase were observed in the XRD analysis, occurring around at 2θ= 28.45° (112), 47° (220/204), and 56° (312/116). Additionally, some secondary phases such as Cu2S and SnS were identified. Raman spectroscopy confirmed the presence of the kesterite phase, with a prominent peak detected at approximately ~336 cm-1, attributed to sulfur atom vibrations within the kesterite structure. Apart from CZTS structure, minor peaks suggesting the presence of the Cu2SnS3 (CTS) phase was detected. EDX analysis revealed compositions with Cu-poor content and Zn-rich content across all samples, with slight variations in sulfurization dwell times affecting the chemical composition. SEM imaging at different magnifications showed alterations in surface morphology and grain structures. Films sulfurized for 30 s and 60 s displayed a granular structure morphology, while extending the dwell time to 120 s resulted in a more compact surface morphology. Optical band gap values ranged between 1.57 and 1.60 eV. PL measurements consistently exhibited strong PL emission around 1.25 eV for all samples, attributed to various transitions within the CZTS structure. The absence of observable band-to-band transitions in the PL measurements indicated the presence of intrinsic defect levels and recombination centers within CZTS. Overall, it was demonstrated in this study that CZTS thin films can be produced on flexible Cu-foils with short sulfurization times, thereby expanding the application areas of CZTS thin-film solar cells.

Nitrogen doped single layer graphene for CZTS-based thin film solar cells

CdS thin films are commonly utilized as a buffer layer in chalcopyrite thin-film solar cells. However, due to the toxic nature of Cadmium (Cd), ongoing efforts are being directed towards exploring alternative options. In this contribution, doped graphene film with remarkable optical and electrical properties has been introduced for the first time as an alternative buffer layer, replacing CdS in CZTS thin-film solar cell application. In this study, nitrogen-doped graphene (N-doped graphene) film was utilized as a substitute buffer layer in the CZTS thin-film solar cell structure, replacing the conventional CdS thin film. For comparative analysis, CZTS/N-doped graphene and CZTS/CdS traditional solar cell structures were fabricated and separately characterized. The CZTS thin films produced were examined through EDX, XRD, SEM, Raman, optical transmission and PL spectroscopy measurements. According to performed analyses, the Cu-poor and Zn-rich kesterite CZTS thin films exhibited a uniform and dense polycrystalline microstructure as observed in surface and cross-sectional SEM images. XRD spectra of the kesterite CZTS thin film displayed predominant peaks corresponding to the (112), (220/204), and (312/116) diffraction planes of the kesterite CZTS phase. Raman spectra showed a dominant peak at ∼336 cm−1 associated with the kesterite CZTS phase. PL emission spectra indicated transitions from the conduction band to defect levels. The CVD-grown doped graphene film exhibited a 3.43 I2D/IG ratio and a 25 cm−1 FWHM of the 2D peak, indicating a single-layer graphene according to Raman analysis. Permanent nitrogen doping with a 2% atomic concentration was confirmed by XPS measurement. The optical transmission measurement of the single layer doped graphene film showed a 95% transmittance value. Nitrogen doping was contributed to decrease the sheet resistance of the graphene film. The Glass/Mo/CZTS/N-doped graphene/i-ZnO/ITO/Al solar cell displayed a VOC of 0.267 V, JSC of 24.6 mA/cm2, FF of 36.46, and η of 2.37%, showing higher FF and Jsc values but lower conversion efficiency compared to the Glass/Mo/CZTS/CdS/i-ZnO/ITO/Al traditional solar cell structure. Hence, the superior working function and transparency properties position the N-doped graphene film as a competitive buffer layer for use in CZTS-based thin-film solar cells.

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.

The effect of step cooling treatment on the microstructure of Cu2ZnSnS4 film and its electric property

Flexible Cu2ZnSnS4 (CZTS) thin-film solar cells have the advantages of high flexibility, lightweight, and easy storage, which can provide portable and clean energy for various portable electronic and communication devices and vehicles. In this work, CZTS thin film deposited on flexible aluminum foil were prepared by vacuum magnetron sputtering and sulfide annealing in a tubular furnace. A step-by-step cooling way was applied to the annealing stage aiming at tuning the formation of CZTS, that is, when the slow cooling reached a target temperature (400 °C, 350 °C, 300 °C, 250 °C), a rapid cooling was triggered by opening the tube furnace lid. The effects of step cooling on the micro structure and property of CZTS film were studied by X-ray diffraction, Raman scattering, energy dispersive spectroscopy, scanning electron microscopy and current-voltage (I-V) characteristic curve test. The experimental results showed that all samples have CZTS phase and the Al/CZTS interface exhibited ohmic contact. And the formation of secondary phases like SnS, Sn2S3 and Cu31S16 in the sample film can be tuned by the step cooling treatments. The sample treated at 300 °C had the highest CZTS content, the average grain size of CZTS was 45 nm and the number of secondary phases was fewer. Beside, the I-V curve revealed that this sample had the lowest resistance. The experimental results in this work indicate the feasibility of Al as a substrate and back electrode for CZTS thin film.

One-Step Hydrothermal Synthesis of Cu2ZnSnS4 Nanoparticles as an Efficient Visible Light Photocatalyst for the Degradation of Congo Red Azo Dye.

A hydrothermal method was successfully employed to synthesize kesterite Cu2ZnSnS4 (CZTS) nanoparticles. X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), field-emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM), and optical ultraviolet-visible (UV-vis) spectroscopy were used for characterization of structural, chemical, morphological, and optical properties. XRD results confirmed that a nanocrystalline CZTS phase corresponding to the kesterite structure was formed. Raman analysis confirmed the existence of single pure phase CZTS. XPS results revealed the oxidation states as Cu+, Zn2+, Sn4+, and S2-. FESEM and TEM micrograph images revealed the presence of nanoparticles with average sizes between 7 nm to 60 nm. The synthesized CZTS nanoparticles bandgap was found to be 1.5 eV which is optimal for solar photocatalytic degradation applications. The properties as a semiconductor material were evaluated through the Mott-Schottky analysis. The photocatalytic activity of CZTS has been investigated through photodegradation of Congo red azo dye solution under solar simulation light irradiation, proving to be an excellent photo-catalyst for CR where 90.2% degradation could be achieved in just 60 min. Furthermore, the prepared CZTS was reusable and can be repeatedly used to remove Congo red dye from aqueous solutions.

Plasmonic resonance and type-I heterojunction interface in SrTiO3/CZTS/Ag nanocomposite for enhanced photocatalytic degradation of organic pollutants

As a novel plasmonic-heterostructure photocatalyst, the Silver (Ag)-modified SrTiO3/Cu2ZnSnS4 ternary nanocomposite was prepared through a co-precipitation method. The incorporation of Cu2ZnSnS4 (CZTS) and Ag into the SrTiO3 host phase reduced the mean particle size from 65 to 38 nm, doubled the surface area, and decreased the bandgap energy from 3.20 to 2.86 eV. A study of UV–visible diffuse reflectance spectroscopy (DRS) and valence band X-ray photoelectron spectroscopy (VB-XPS) confirmed the formation of type-I heterostructure charge transfer mechanisms between SrTiO3 and CZTS phases. Results from photoluminescence (PL), electrochemical impedance spectroscopy (EIS), and transient photocurrent experiments indicated that the ternary nanocomposite exhibits less internal resistance and a higher capacity for charge carrier separation. The effect of different photocatalytic experiment parameters on the photodegradation performance has been studied. In this regard, 90 min visible light irradiation time, 5 mg/L initial dye concentration, and 1 g/L powder dosage were found to be the best values. The designed system exhibited excellent photocatalytic performance, in which more than 99% of methylene blue (MB) dye degraded under optimum conditions. The reaction mechanism and kinetics were comparatively investigated in-depth. After a four-run cyclic experiment, the prepared photocatalyst exhibited high stability and reusability. The prepared sample demonstrated photocatalytic efficiencies of 87%, 66%, and 71% for the degradation of methyl orange (MO), Rhodamine-B (RhB), and Ciprofloxacin (CIP) pollutants, respectively.

Impact of the ZnS layer position in a stacked precursor film on the properties of CZTS films grown on flexible molybdenum substrates

In the present study, CZTS thin films were prepared by annealing and reaction of Cu–Sn–ZnS precursor layers. First, sputter deposition was carried out on flexible molybdenum (Mo) foil to form Mo-foil/CuSn/ZnS/Cu, Mo-foil/CuSn/Cu/ZnS and Mo-foil/ZnS/CuSn/Cu stacked precursor structures. Annealing process was performed in sulfur atmosphere using Rapid Thermal Processing (RTP) method to obtain kesterite CZTS phase in the reacted layers. All prepared precursors and CZTS thin films displayed Cu-poor and Zn-rich chemical composition, as targeted. XRD patterns of CZTS samples showed that the kesterite phase was obtained in all samples regardless of the stacking order of the precursor films. However, the full width at half maximum (FWHM) values of the (112) preferential peaks extracted from the XRD patterns, and the corresponding structural parameters (crystallite size and microstrain), indicated that the Mo-foil/ZnS/CuSn/Cu precursor structure yielded more promising crystalline quality. The occurrence of kesterite phase in all samples and existence of low amount of CTS phase were verified by Raman spectroscopy measurements. The CZTS sample prepared employing the Mo-foil/ZnS/CuSn/Cu precursor film structure presented more prominent, homogenous and compact surface microstructure as observed in SEM images. Optical band gap values were found to be in the range of 1.44–1.50 eV. The room temperature photoluminescence (PL) measurements showed that the transitions from the conduction band to intrinsic defect levels dominated the spectra instead of the band-to-band transitions. Electrical characterization of the films showed that Mo-foil/CuSn/ZnS/Cu and Mo-foil/ZnS/CuSn/Cu precursor films yielded lower electrical resistivity and higher carrier concentration due to better crystalline quality. Overall, it was seen that the CZTS thin films produced using the Mo-foil/ZnS/CuSn/Cu stacked precursor layers displayed better properties in terms of crystalline quality, surface microstructure, and optical and electrical properties, which are favorable for photovoltaic applications.

Biological investigation of sonochemically synthesized CZTS nanoparticles

Cu2ZnSnS4 (CZTS) nanoparticles (NPs) are synthesized by sonochemical technique. The composition analysis showed the synthesized NPs to be stoichiometric. The X-ray diffraction confirms the CZTS phase and tetragonal unit cell structure. Three peaks corresponding to CZTS have been observed in Raman spectroscopy positioned at 293.47 cm−1, 373.8 cm−1, and 336.67 cm−1. The electron diffraction in the selected area showed faded rings with spot patterns indicating crystalline nature. The CZTS NPs have a direct optical bandgap of 1.62 eV, being ascertained by optical absorbance spectroscopy. The CZTS NPs antibacterial activity is determined against pathogenic gram-negative (E. coli, P. aeruginosa, P. vulgaris, and E. aerogenes) and gram-positive (S. aureus) bacteria by measuring the inhibition zone. The 2, 2-diphenyl-1-picrylhydrazyl assay is employed in deciding the antioxidant efficacy of CZTS NPs. The cytotoxicity of CZTS NPs is evaluated in Brine shrimp (Artemia salina) eggs hatched in synthetic seawater made from 38 g/l commercial sea salt. The findings are discussed in detail.

Integration of single layer graphene into CZTS thin film solar cells

In this study, CZTS samples were produced on Mo and graphene/Mo coated glass substrates using quaternary target. The CZTS thin films deposited by RF magnetron sputtering were annealed using rapid thermal processing (RTP) method in sulphur atmosphere at 500, 525, and 550 °C so as to obtain glass/Mo/CZTS and glass/Mo/graphene/CZTS (g-CZTS) structures. The obtained CZTS and g-CZTS thin films were then characterized by several methods such as EDX, XRD, Raman spectroscopy, SEM etc. The EDX data demonstrated that all CZTS thin films had Cu poor composition regardless of the sulfurization temperature and increasing the temperature led to Sn loss from the films. Diffraction peaks of kesterite CZTS phase were observed in all the samples; additionally, SnS and CuS secondary phases were also observed in CZTS samples annealed at 500 °C. The crystallite size of the CZTS thin films were found to be increasing with both increasing annealing temperature and use of graphene film as an inter-layer. The creation of kesterite phase with a very small CTS phase in all the samples were verified by the Raman spectroscopy measurement. The SEM images of the samples indicated that using graphene improves the crystalline quality of the CZTS films and contributes to forming more compact, homogenous and larger crystal structure. The determined optical band gap values varied from 1.41 to 1.44 eV depending on the Sn-content of the samples. The produced solar cells selected from the more promising absorber layers showed that implementing graphene in CZTS cell structure enhanced the conversion efficiency from 2.40% to 3.52% due to improvement of crystalline quality of the absorber layer.

Non-stoichiometric effect and disorder in as-prepared Cu2ZnSnS4 films deposited at different temperatures by ultrasonic spray pyrolysis

A better understanding of its crystal structure, the formation of possible secondary phases, defects and Cu–Zn disorder effects is needed to improve the photovoltaic device performance of CZTS films. In this direction, the effect of deposition temperature on the structural inhomogeneities, such as secondary phases and Cu–Zn disorder, etc. as well as opto-electrical properties of CZTS were experimentally examined. For this purpose, a non-stoichiometric spraying solution was prepared and ultrasonically sprayed onto glass substrates at different deposition temperatures (350 °C, 400 °C, 450 °C, and 500 °C) to obtain CZTS films. Afterward, the structural, morphological, elemental, optical, and electrical properties of the deposited films were investigated in detail. By Lorentzian deconvolution of Raman spectra, 14 Raman vibrational modes were detected and seven of these were assigned to the secondary phases. Also, the ordered-kesterite phase (337 cm−1) of CZTS was found to crystallize along with the disordered-kesterite phase (329 cm−1) due to the disorder of the cation (Cu–Zn) sublattice. Optical band gaps for CZTS films decreased from 1.89 eV to 1.42 eV with increasing in deposition temperature. It was seen that not only optical band gaps but also Cu–Zn disorder and the amount of secondary phases in CZTS films tightly depend on the deposition temperature.

Facile single step synthesis of Cu2ZnSnS4 thin films by sputtering from a single target and their electrical characterization

Facile deposition of ternary semiconducting Cu2ZnSnS4 (CZTS) thin films has been a challenge due to a very narrow range of single phase stability in the Cu-Zn-Sn-S system. While sputtering has been a very efficient method of growth of various optoelectronic thin films, the formation of secondary phases should be suppressed during sputter deposition of CZTS films. Differently with the reported studies on deposition of a precursor film followed by a delicately - controlled sulfurization process required for the formation of the kesterite CZTS phase, we demonstrate a single step synthesis route to grow phase pure CZTS thin films using a single elementary target with excess Cu by RF magnetron sputtering at a substrate temperature of 450 °C. The route did not require any post-deposition sulfurization. These films had an optical band gap of ~1.6 eV and white light sensitivity> 200% at a bias potential of 5 V, highly suitable for photovoltaic and photocatalytic activities. Detailed electro-impedance analyses from Nyquist, Bode and Mott-Schottky plots of a Mo/CZTS/Pt/electrolyte device revealed p-type conductivity with a flat band potential of 0.51 V (reversible hydrogen electrode), carrier concentration of 6.2 × 1017 cm−3 and a carrier life time as high as of ~17 μs.

A rapid microwave-assisted method of synthesizing wurtzite Cu2ZnSnS4 in a novel solvent and its controlled phase evolution

Stable pure wurtzite Cu2ZnSnS4 (CZTS) microparticles are successfully synthesized and the phase control evolution is studied, where a mixture of ethylene glycol (EG) and triethylenetetramine (TETA) is used in conjunction with a rapid and low-cost microwave-assisted method to control the crystalline phases of the particles. The CZTS phase is mainly controlled by changing the reaction time, reaction power, surfactant vs. raw material ratio. The particles are characterized with X-ray diffraction, Raman spectroscopy, scanning electron microscope, transmission electron microscope and UV–vis spectrophotometer. The results show that when EG and TETA are mixed in a ratio of 1:6 and the reaction power is 800 W, CZTS in pure wurtzite phase is obtained rapidly when the raw material ratio is Cu: Zn: Sn: S = 2 : 1.25: 1: 6 and the reaction time is 120 s. The phase transition can be effectively controlled by controlling the reaction conditions such as raw material ratio, reaction power and reaction time.

Electrodeposition assisted sol-gel process to prepare CZTS thin films

The traditional sol-gel process usually takes a long time to form a stable Cu2ZnSnS4 (CZTS) sol-gel solution, which increases the whole process time. In this paper, an electrodeposition assisted sol-gel process was employed to reduce the solution preparation time. Cu was electrodeposited on Mo surface and ZnSnS sol-gel was rotated on Cu surface to prepare CZTS films. The solution preparation time was reduced from 12h to 30min. The mechanism of CZTS phase formation with sol-gel method assisted by electrodeposition was studied. Cu3SnS4 phase was formed during the electrodeposition assisted sol-gel process, while Cu2SnS3 phase was formed when the CZTS precursor during sol-gel process. Cu content was rich at the beginning of the reaction to form Cu3SnS4 during the electrodeposited assisted sol-gel process. CZTS films with Cu/(Zn + Sn) of 0.84 and Zn/Sn of 1.03 were prepared by sol-gel method assisted by electrodeposition. Compared with CZTS films prepared by sol-gel method, CZTS films prepared by this method have larger and more uniform grains. It is also found that the thickness of MoS2 layer was thinner than the one prepared by sol-gel method.

Insight into the Growth Mechanism of Mixed Phase CZTS and the Photocatalytic Performance.

In this work, CZTS particles with a mixed phase of wurtzite and kesterite were synthesized by the solvothermal method. The time-dependent XRD patterns, Raman spectra, SEM, and EDS analysis were employed to study the growth mechanism of CZTS. The results revealed that the formation of CZTS started from the nucleation of monoclinic Cu7S4 seeds, followed by the successive incorporation of Zn2+ and Sn4+ ions. Additionally, the diffusion of Zn2+ into Cu7S4 crystal lattice is much faster than that of Sn4+. With increasing time, CZTS undergoes a phase transformation from metastable wurtzite to steady kesterite. The morphology of CZTS tends to change from spherical-like to flower-like architecture. The mixed-phase CZTS with a bandgap of 1.5 eV exhibited strong visible light absorption, good capability for photoelectric conversion, and suitable band alignment, which makes it capable to produce H2 production and degrade RhB under simulated solar illumination.

Metastable wurtzite phase Cu2ZnSnS4 nanocrystal synthesis and application in solar cell

In this article, we propose a simple solution phase synthesis of wurtzite phase Cu2ZnSnS4 (W-CZTS) nanocrystals incorporating dodecanethiol mixed with oleylamine as sulfur source. The wurtzite phase formation was confirmed by XRD and Raman analysis. The synthesized W-CZTS nanocrystals displayed plate-like structure as observed by TEM imaging. The solar cell device fabricated with W-CZTS as p-type light absorber layer exhibited very good behaviour of p-n junction diode with n-type CdS layer and delivered the efficiency of 2.11% without any high temperature processing of absorber layer. The efficiency delivered by solar cell device utilizing wurtzite phase delivered slightly higher efficiency than using kesterite phase CZTS under similar conditions.

Solvent engineering to regulate the phase of copper zinc tin sulfide nanocrystals.

Copper zinc tin sulfide (Cu2ZnSnS4, CZTS) is attracting interest in photovoltaic applications due to its proper band gap, low cost and low toxicity. It has been found that two phases can be fabricated, i.e. kesterite and wurtzite CZTS structures. Though kesterite CZTS is proven to be thermodynamically stable, the free energy difference between kesterite and wurtzite CZTS is rather small. So, wurtzite CZTS can also stably exist under ambient conditions. Controlling the phase formation can expand the dimensions to optimize the performance of applications based on CZTS. In this study, we found that phase control can be achieved by simply using a mixed solvent of ethylene glycol and triethylenetetramine (TETA) in a two-stage heating process. It is found that the incorporation of the reductive solvent of TETA during the 1st heating process converts the phase of the precipitates from CuS (TETA poor) to Cu7S4 (TETA rich). In the subsequent 2nd heating stage, the phase of the final products is determined to be kesterite CZTS originating from CuS and wurtzite CZTS from Cu7S4, respectively. Thus, the key to control the phases of the final products is to control the chemical environment of Cu under Cu1+-rich or Cu2+-rich conditions in the fabrication process, which corresponds to the phase of the final products of wurtzite CZTS or kesterite CZTS, respectively. This summarized principle can not only be used to explain the previous versatile experimental results but also to guide the controlled synthesis of various phases of CZTS and CZTS-like materials in applications.

Investigation of CZTS absorber layer deposited by spin coating technique for photovoltaic applications

In this work we prepared and deposited Cu2ZnSnS4 (CZTS) absorber layers by sol gel spin coating technique on ordinary glass substrates. We studied the influence of annealing time on structural, compositional, morphological, optical and electrical properties of films at different times of 5, 10 and 20 min, respectively. The films have been analyzed by different characterization techniques such as X-ray diffractometer (XRD), Raman spectroscopy, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), UV–visible-NIR spectrophotometer and four point probe method. XRD patterns showed pure kesterite CZTS with preferential orientation along (112) plane and calculated lattice parameters a = b = 0.5428 nm and c = 1.0849 nm. Raman scattering measurements confirmed the existence of a single CZTS phase showing a single peak at 338 cm−1. SEM images showed compact, uniform and densely surface morphology. EDS analysis indicated near-stoichiometric CZTS films, UV–Visible-NIR spectrophotometer showed that the optical band gap energy of CZTS thin films is found to be between 1.48 and 1.7 eV. Four point probe measurements exhibited a suitable electrical conductivity in the range 3.03–3.44 (Ω.cm)−1. These properties make the as-synthesized CZTS films an appropriate material as absorber layer in solar cells applications.