Kesterite CZTS Research Articles

Enhancing the performance of Cu2ZnSnS4 solar cell fabricated via successive ionic layer adsorption and reaction method by optimizing the annealing process

Kesterite Cu2ZnSnS4 (CZTS) solar cells are regarded as a promising photovoltaic technology owing to the non-toxic and earth-abundant constitutes. With the application of scalable and low-cost solution methods, the possibility of its commercialization can be further increased. This work explores preparing prominent CZTS films by an economically feasible successive ionic adsorption and reaction (SILAR) synthesis method. The obtained precursor with the Mo/ZnS/Cu2SnS3 structure requires appropriate substantial annealing under a chalcogen atmosphere to form kesterite CZTS films. The annealing process is therefore optimized to improve the film quality and the performance of solar cells. Specifically, the optimal annealing condition is determined by adjusting the annealing temperature and holding time, respectively. The CZTS film annealed at 580 °C for 60 min demonstrates better film quality in terms of surface morphology, crystallinity, and phase purity. Consequently, CZTS solar cells fabricated with the optimal absorber exhibit a preferable efficiency of up to 4.26%.

Solution-processed pure Cu2ZnSnS4/CdS thin film solar cell with 7.5% efficiency

Abstract The kesterite Cu2ZnSnS4 (CZTS) thin-film solar cell is one of the emerging solar cells. The Zn and Sn materials were prepared to substitute the rare In and Ga materials in previous CuInGaS2 cell generation. However, the secondary phase formation and the non-uniform film formation during the solution process affect deteriorating cell performance. By considering the CZTS kesterite structure, secondary phases, bandgap, and absorbance, this work aims to present the novel achievement of solution processed-pure Cu2ZnSnS4/CdS solar cell. The solar cell was made with the structure of Mo/Cu2ZnSnS4/CdS/ITO/Ag consisting of 21 subcells. The characterizations were employed through X-ray diffraction (XRD), external quantum efficiency, energy gap, and J-V curve. To the best knowledge, without further cation exchange modification and the atomic ratio of Zn/Sn = 1.26 and Cu/(Zn + Sn) = 0.86, the fabricated solar cell exhibits the novel achievement for the pure Cu2ZnSnS4/CdS standard solution process with the power conversion efficiency of 7.5% with 1.43 eV bandgap and 83.5% external quantum efficiency at 570 nm. The correlation between kesterite, secondary phases, bandgap, absorbance, dan cell performance statistics were further discussed. This work implied considering the atomic ratio of Cu-poor, Zn-rich, and the film uniformity during the spin coating process; it plays a significant role in achieving high-performance solution-processed CZTS solar cells.

Copper concentration effect on physical properties of ultrasonically sprayed Cu2ZnSnS4 absorber thin films for solar cell applications

Cu2ZnSnS4 (CZTS) thin films have been successfully deposited on glass substrate using ultrasonic spray pyrolysis (USP) technique with different copper concentrations ranging from 0.005 to 0.020 M. The effect of copper concentration on the structural, morphological and optoelectrical properties of deposited films has been investigated. Choice of USP method and copper concentration was found to have a crucial role in stoichiometry, band gap and conductivity of sprayed CZTS thin films. X-ray diffraction indicated that all deposited films have CZTS Kesterite structure with a preferential orientation along (112) plane confirmed by Raman scattering measurements. Copper sulfide (CuS) is present as a secondary phase in all films. The presence of this secondary phase causes films optical band broadening. Good film with nearly stoichiometric CZTS film and desirable band gap of 1.51 eV was obtained at copper concentration of 0.015 M. This result indicates that this film is suitable for being applied as an absorber layer in photovoltaic solar cells.

Design and characterization of a chloride-free organic copper solution: Electrochemical synthesis of Zn/Cu/Sn precursor stack for CZTS-based photoconversion devices

In the present study, an ethylene glycol-based electrolyte is used to electrodeposit copper onto zinc for the synthesis of the Zn/Cu/Sn stack, precursor of Cu2ZnSnS4. The employed solution contains diethanolamine (DEA) which supports the formation of amine-complexes, whose features are studied by UV–vis absorption, ESI-MS, and FTIR measurements, providing insight on the optimal concentration of DEA for copper complexation. Cyclic voltammetries (CVs) are carried out at increasing [DEA]/[Cu2+] ratios, highlighting the amine effect on the reduction potential of the copper species. The displacement reaction between copper and zinc is investigated by immersion potential measurements, showing a direct correlation to the voltammetric data. The optimized copper solution resulted in a negligible displacement contribution, allowing the electrochemical synthesis of Mo(sub)/Zn/Cu/Sn stack on a relatively large area (4 cm2). The metallic precursor is analyzed by SEM/EDS, AFM, XRD, and GDOES techniques. Finally, the kesterite CZTS phase is obtained through reactive annealing with elemental sulfur and it is characterized by SEM/EDS, XRD, and Raman spectroscopy. Photoelectrochemical water splitting on CZTS/CdS/Pt heterostructure is carried out in an aqueous solution at pH 6.85, showing a photocurrent of -5.05 mA/cm2 at 0 V vs RHE. A maximum applied bias photon-to-current efficiency (ABPE) value of 2.15% was found at 0.84 V bias.

Fabrication of Cu-rich CZTS thin films by two-stage process: Effect of gas flow-rate in sulfurization process

In this study, CZTS thin films were prepared using a two-stage process consisting of sputter deposition of Cu, Sn and ZnS layers on the glass substrates to form CuSn/ZnS/Cu stacked precursor films followed by sulfurization process under various flow-rate (0, 20, 40, 60, 80, 100 sccm) of Ar+H2 mix gas in a tubular furnace. The EDX measurements of the precursor and reacted films are Cu-rich and Zn-rich composition. However, Zn and Sn loss was observed for samples annealed under the flow-rate of gas above the 60 sccm. The XRD pattern of the samples showed diffraction peaks of pure kesterite CZTS structure and the FWHM values extracted from their XRD patterns and W-H plot calculations demonstrated that CZTS-40 thin film had a more desired crystallite size. The Raman spectra of the samples confirmed the formation of CZTS phase for all samples and indicated the formation of some secondary phases such as Cu2SnS3, SnS2, Sn2S3 except for CZTS-40 thin film. All the samples displayed dense and polycrystalline microstructure according to their SEM images. The optical band gap values of CZTS samples showed variation between 1.40 and 1.48 eV. The room-temperature PL spectra of the samples revealed a broad band that had a peak value at around 1.36–1.40 eV that are close to the optical band gap values for prepared CZTS samples.

Anion exchange induced formation of kesterite copper zinc tin sulphide-copper zinc tin selenide nanoheterostructures.

We report the colloidal synthesis of quaternary kesterite CZTS-CZTSe heterostructures via anion exchange reactions on a kesterite CZTS template. The crystal phase selectivity during the synthesis (kesterite vs. wurtzite) is due to the initial nucleation of cubic Cu9S5 seeds, followed by incorporation of Zn and Sn. Upon injection of Se-precursor, which triggered simultaneous anion exchange and overgrowth of the pristine CZTS template, sandwich CZTS-CZTSe (core-tip) nanoheterostructures were obtained. X-ray photoelectron spectroscopy (XPS) and optical band gap measurement results suggest a change of intrinsic electronic structure of CZTS by Se-treatment. Our study not only provides insight into mechanisms of formation of kesterite CZTS nanocrystals (NCs) and subsequent anion exchange reactions, but also opens doors to access novel CZTSSe nanostructures for potential applications.

Origin of the low conversion efficiency in Cu2ZnSnS4 kesterite solar cells: the actual role of cation disorder

The role of cation disorder in the persistently low efficiency of CZTS kesterite solar cells is elucidated.

Characterization of Cu2ZnSnS4 thin films deposited by one-step thermal evaporation for a third generation solar cell

In this study, one-step thermal evaporation was employed for the fabrication of phase-pure CZTS thin films on glass substrates from single crystalline Cu-poor ingot grown by Bridgman technique. Structural analyses revealed the formation of a mono-phase CZTS kesterite structure for the thin films annealed at 450 °C under N2 atmosphere. The AFM measurements demonstrated significant morphological changes in films with increasing the annealing temperature from 200 °C to 450 °C, supporting the results obtained via XRD and Raman studies. From the optical measurements, the band gap was estimated to be 1.47 eV for the CZTS film annealed at 450 °C, which is close to the optimum value required for photovoltaic applications. As a device application of the optimized CZTS thin films, an attempt was made to construct a TiO2 NRs based and CdS-free FTO/TiO2 NRs/CZTS/Ag superstrate CZTS solar cells. TiO2 NRs were grown by hydrothermal technique, which offers a simple and a cost-effective route for large-scale production of one-dimensional nanostructures. The solar cell exhibited an open-circuit voltage of 0.35 V, a short-circuit current density of 7.28 mA/cm2, a fill factor of 23.9% and a power conversion efficiency of 0.61%, the highest efficiency recorded so far for a single-dimensional TiO2 nanostructures based superstrate CZTS solar cell.

Study of the semiconducting properties of Cu2ZnSnS4 thin films grown by ultrasonic spray pyrolysis of water-dissolved precursors

Cu2ZnSnS4 (CZTS) thin films were deposited on glass-slide substrates by ultrasonic spray pyrolysis at the substrate temperatures in the 330–420 °C range, using water–ethanol solutions containing CuCl2–H2O, ZnCl2, SnCl2, and (NH2)2CS (thiourea). After being deposited, CZTS films were annealed under vacuum and then characterized in regarding their structural and optical properties. The X-ray diffraction and Raman spectroscopy studies indicated that CZTS thin films with kesterite as predominant phase could be obtained. The X-ray diffraction patterns of all deposited samples displayed diffraction peaks corresponding to the planes (112), (220), and (312) of kesterite CZTS and diffraction peaks belonging to phases other than CZTS were apparently undetectable for the X-ray technique. Furthermore, their Raman spectra were featured for a widely structured Raman band in the 200–400 cm−1 wavenumber area. After being deconvoluted, Raman peaks belonging only to kesterite CZTS were revealed. However, a further analysis of the UV–Vis absorbance spectra indicated all our films strongly absorbs in this spectral region. In the low photon energy region (< 1.5 eV), Tauc plots revealed electron transitions with characteristic energy values in the 1.15–1.34 eV range, which could be attributed at the presence of tetragonal Cu2SnS3 and point defects (VS and VZn) into CZTS. All prepared CZTS films display the p-type conductivity as verified by Hall measurements.

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.

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.

High efficient hybrid bulk hetero junction thin-film solar cell embedded with kesterite Cu2ZnSnS4 quantum dots

The photovoltaic performance of kesterite Cu 2 ZnSnS 4 (CZTS) quantum dot (QD) incorporated poly(3-hexylthiophene-2,5-diyl) (Alvarado et al., 1998; Alvarado et al., 1998) [6,6]: phenyl-C61butyric acid hexyl ester (P3HT:PCBH) polymer matrix based organic hybrid heterojunction solar cell configuration is investigated. The inorganic filler material CZTS QDs with P3HT:PCBH matrix, forms double bulk hetero junction (BHJ) throughout in the active layer, which facilitates rapid exciton dissocitaion process at P3HT:PCBH and CZTS:PCBH interfaces that results effective charge carrier separation. The prepared active layer material has been characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), x-ray diffraction (XRD), Raman and fourier transform infra red (FTIR). The enhanced optical absorbance of prepared hybrid structure has been verified by UV–Visible analysis. It has been observed that the improvement in photo conversion efficiency (PCE) from 2.36% for the solar cell device P3HT:PCBH to 4.12% for CZTS QD based P3HT:PCBH hybrid organic solar cell device. This dramtaic increase in PCE, is mainly due to the significant enhancement in short-circuit current density (J sc ) from 7.6 mA/cm 2 to 11.2 mA/cm 2 . That suggests, the incorporation of p-type kesterite CZTS QDs into P3HT:PCBH polymer matrix enhances the effective exciton dissociation at interfaces resulting charge separation and their fast extraction to electrodes inhibiting e − /h + pair recombination. Furthermore, the hybrid solar cell shows remarkable time stability retaining 80% of original PCE measured after 30 days under ambient environment conditions. The hybrid organic solar cell device shows thermal stability by retaining 95.6% of its intial efficiency measured which has been tested in the temperature range 20–80 °C. • Photovoltaic performance of CZTS QDs:P3HT:PCBH hybrid thin film solar cell is investigated. • PCE of hybrid device has been observed to enhance from 2.36% to 4.12%. • It shows time and thermal stability retaining 80% and 95.6% efficiency.

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.

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.

Intermittent sulfurization—a method promoting Macro-Porous Cu-Poor Zn-Rich—kesterite CZTS as HTM for inverted perovskite solar cell application

Porous semiconductors have emerged as a lucrative apparatus for energy-harvesting applications with more exceptional ability as compared to their bulk counterpart. Exposure of a new porous formation strategy for the abundant semiconductor CZTS could initiate an extensive exploration for solar cell applications. Available porous formation strategies for the CZTS have neglected a significant factor of its compositional balance, which needs to be assisted carefully. In this work, intermittent sulfurization technique is used to promote macro-porous CZTS towards perovskite solar cell applications. This technique not only promotes the macro-porosity of CZTS but also successfully controls its compositional balance to fulfill the favorable Cu-poor Zn-rich condition. Every tuned step of this technique causes a different morphology and composition, which has been investigated by FESEM and EDX mapping. Meanwhile, characterization of phase, crystallinity, and optical bandgap have also been investigated by XRD, Raman spectroscopy, and UV–Vis spectroscopy, respectively, for the resulted in macro-porous Kesterite CZTS. Inverted (p-i-n)-structured perovskite solar cell with p-type macro-porous CZTS as hole transporter material delivered 3.33% power conversion efficiency. Synthesis of perovskite material and electron transporting material along with the fabrication of (p-i-n)-structured perovskite solar cells have also been detailed here.

Facile solvothermal synthesis of Cu2ZnSn1-xGexS4 nanocrystals: Effect of Ge content on optical and electrical properties

Controlled incorporation of extrinsic elements in Cu2ZnSnS4 (CZTS) matrix has been proven to be a successful approach to improve the device efficiency of kesterite solar cells. In this paper, we have reported the synthesis of polycrystalline Cu2ZnSn1-xGexS4 (CZTGS) nanocrystals (NCs) (0≤x≤1;x=[Ge]/[Sn+Ge]) by facile and cost-effective solvothermal method. The powder samples were annealed under inert atmosphere in presence of sulfur powder to improve crystallinity. The effect of Ge alloying on structural, morphological, compositional, optical and electrical properties was studied using different characterization tools. X-ray diffraction analysis revealed the structural evolution of tetragonal Cu2ZnSnS4 (CZTS) to orthorhombic Cu2ZnGeS4 (CZGS) with the increase of Ge/Sn ratio. Characteristic Raman peaks were shifted to higher frequency with increasing Ge concentration. The transition of quasi-spherical morphology for kesterite CZTS into rod-like shape for orthorhombic CZGS was evidenced by Transmission electron microscopy. The band gap of resulting CZTGS NCs were found to increase from 1.37 to 1.96 eV by increasing Ge content. The doctor-blade printed CZTGS films were p-type. By increasing Ge concentration, carrier concentration was increased gradually, while electrical resistivity and hole mobility were found to decrease. The electrical properties suggest that a relatively low Ge incorporation might be beneficial for their application as photoabsorber in photovoltaic devices.

Investigations of the structural, optoelectronic and band alignment properties of Cu2ZnSnS4 prepared by hot-injection method towards low-cost photovoltaic applications

Cu2ZnSnS4 is a promising, versatile and inexpensive quaternary semiconductor with suitable optoelectronic properties for solar energy conversion. In this work, we report the synthesis of CZTS nanocrystals (NCs) using low-cost homemade hot-injection method. Oleylamine was used as both the binder and stabilizer for the CZTS NCs during the growth process. Detailed investigation of the influence of sulphur concentration and reaction temperature on the structural, stoichiometric, morphological, and optoelectronic attributes of CZTS NCs was carried out. The XRD, Raman, and TEM measurements confirm the formation of phase-pure tetragonal kesterite CZTS NCs. The synthesized CZTS NCs exhibit particle sizes in the range of 15–30 nm and display strong optical absorption in the visible region. The nearly optimal chemical composition of the CZTS NCs was confirmed by energy dispersive X-ray spectroscopy. UV–Visible spectroscopy and electrochemical measurements predict the band gap of the CZTS NCs in the range of 1.3–1.6 eV, which is very close to the optimum values for the fabrication of single junction solar cells. The estimated conduction band offset (CBO) and valence band offset (VBO) of the CZTS-3M/CdS heterostructure are predicted as 0.11 and 0.98 eV, respectively, whereas for CZTS-225 °C/CdS heterostructure, CBO and VBO are 0.10 and 1.0 eV, respectively. The small conduction band offset measured at the CZTS/CdS interface are encouraging characteristics for the carrier transport and the deeper understating of band alignment and interface properties provides a hopeful approach for designing higher efficiency and more efficient carrier separation in CZTS solar cells.

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.

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.