Copper Zinc Tin Sulfide Thin Films Research Articles

Recent Progress and Challenges in Controlling Secondary Phases in Kesterite CZT(S/Se) Thin Films: A Critical Review

Kesterite-based copper zinc tin sulfide (CZTS) and copper zinc tin selenide (CZTSe) thin films have attracted considerable attention as promising materials for sustainable and cost-effective thin-film solar cells. However, the successful integration of these materials into photovoltaic devices is hindered by the coexistence of secondary phases, which can significantly affect device performance and stability. This review article provides a comprehensive overview of recent progress and challenges in controlling secondary phases in kesterite CZTS and CZTSe thin films. Drawing from relevant studies, we discuss state-of-the-art strategies and techniques employed to mitigate the formation of secondary phases. These include a range of deposition methods, such as electrodeposition, sol-gel, spray pyrolysis, evaporation, pulsed laser deposition, and sputtering, each presenting distinct benefits in enhancing phase purity. This study highlights the importance of employing various characterization techniques, such as X-ray diffraction, Raman spectroscopy, scanning electron microscopy, and energy-dispersive X-ray spectroscopy, for the precise identification of secondary phases in CZTS and CZTSe thin films. Furthermore, the review discusses innovative strategies and techniques aimed at mitigating the occurrence of secondary phases, including process optimization, compositional tuning, and post-deposition treatments. These approaches offer promising avenues for enhancing the purity and performance of kesterite-based thin-film solar cells. Challenges and open questions in this field are addressed, and potential future research directions are proposed. By comprehensively analyzing recent advancements, this review contributes to a deeper understanding of secondary phase-related issues in kesterite CZT(S/Se) thin films, paving the way for enhanced performance and commercial viability of thin-film solar cell technologies.

Enhancing the optoelectronic performance of CZTS thin films through cobalt doping via nebulizer-assisted spray pyrolysis technique

In the current investigation, the influence of cobalt doping on the optoelectronic performance of Copper Zinc Tin Sulfide (CZTS) thin films is analyzed. An economic route of synthesis is achieved by employing nebulizer-assisted spray pyrolysis technique. The cobalt concentration is varied from 1 to 5 wt%. The structural, morphological, optical and electrical studies were also made to understand the underlying mechanism that supports the enhancement of photo detecting-capability of these films. It is observed from the XRD studies that initially the doped cobalt replaces zinc in the CZTS lattice. When the concentration of Co was increased beyond 3 wt%, in addition to CZTS we could observe the phase of Copper Cobalt Tin Sulfide (CCTS). At higher concentration the samples exhibit the presence of two phases simultaneously with CCTS as dominant phase. Morphological images from SEM show larger distinct particles for 3% Co doped CZTS. A better absorption in the visible region is witnessed for all the films. The band gap was found to increase with the increase in the concentration of the dopant atom upto 3 wt%. The photoluminescence analysis supports a near-band edge emission around 735 nm. The photocurrent was found to be maximum for 3% Co doped CZTS sample. The rise time and fall time of Co-doped samples becomes halved when compared with the pristine sample. Our research demonstrates the potential applications of CZTS:Co thin films in the realm of photodetectors.

Synthesis and characterization of lithium-doped copper zinc tin sulfide (CZTS) thin films

The non-toxic nature and remarkable optoelectronic properties of kesterite (Cu2ZnSnS4 and CZTS) make CZTS a potential candidate for solar cell absorber layer material. Since alkali metal doping has shown a performance boost of active layers of solar cells, this work investigates the effects of significant lithium doping on sol-gel-produced CZTS thin films. CZTS- and lithium (Li)-doped CZTS thin films were prepared using the spin coating technique. The variation of structural, morphological, and optical properties of CZTS due to Li-doping has been studied by x-ray diffraction, scanning electron microscopy, and UV–visible spectroscopy techniques. All the synthesized LixCu2−xZnSnS4 (x = 0, 0.2, 0.4, 0.6) films showed fine crystallinity with average crystallite sizes of 4.745, 6.013, 6.255, and 6.404 nm, respectively. The average grain size decreases from 0.336 to 0.310 µm via increasing Li concentration. The inclusion of Li increased the bandgap energy ranges from 1.5 to 1.808 eV. The Li0.6Cu1.4ZnSnS4 thin showed the highest absorption coefficient of 3.505 × 104 cm−1 among all the prepared thin films. A high optical conductivity over 1014 s−1 was observed for CZTS, which further increased with an increased Li concentration. The synthesized structures showed enhanced characteristics suitable for solar cell application.

Low-cost kesterite (CZTS) bilayers as an effective hole-transport layer for perovskite solar cells

This study investigates the utility of Copper Zinc Tin Sulfide (CZTS) thin films as inorganic hole-transporting layers (HTLs) in low-temperature perovskite solar cells (PSCs). The primary goal is to improve power conversion efficiencies (PCE) in PSCs using CZTS thin films fabricated through solution-based methods, with CH3NH3PbI3 perovskite and ZnO serving as the light-absorbing and electron-transporting components, respectively. Precise control over CZTS thin film growth significantly influences the formation of uniform perovskite layers. The study underscores the importance of achieving dense ZnO films with suitable grain sizes to confirm consistent coverage of perovskite films, enabling efficient charge transport while reducing recombination at the CZTS/perovskite interface. Results reveal that CZTS/CZTS bilayers exhibit superior photoelectrochemical performance compared to conventional CZTS(A)/FTO and CZTS(B)/CZTS(A) configurations. Evaluation of water splitting performance demonstrates that the CZTS/CZTS bilayer photoelectrode achieves the maximum photocurrent density, reaching 12 mA/cm2 vs. Ag/AgCl, with an Incident Photon-to-Current Efficiency of 9 % at 400 nm and an applied potential of 0.4V vs. Ag/AgCl. The study comprehensively examines CZTS impact on PSC photovoltaic properties and stability, culminating in a high-performance device with a PCE potential of up to 7 %. This underscores the pivotal role of CZTS− perovskite contacts in determining PSC photovoltaic performance and highlights CZTS potential as a versatile HTM for various PSCs designs.

Photosensitivity reversal in solution-processed Copper Zinc Tin Sulphide/Cadmium Sulphide superstrate junction

Inverse photosensitivity is a sought-after property for the development of photonic devices and non-volatile memories with low power conversion. Herein, we report on the development of a superstrate-type thin film junction exhibiting inverse photosensitivity which does not involve the use of a pricy transparent conducting oxide layer, providing a method for engineering low-cost thin film devices. Sequential ionic layer adsorption reaction (SILAR) was used to grow Copper Zinc Tin Sulphide (CZTS) and Cadmium sulphide (CdS) large area thin film p-n diode junction. Uniform CZTS thin films with an area of ∼10 cm2 which were free of pin holes or voids could be deposited using an optimized SILAR process recipe. The grown CZTS films exhibited an electrical resistivity of 4.4 × 10−4 Ωm using silver (Ag) electrodes. CdS thin films were sub-sequentially grown over the CZTS layer to form a p-n junction. A knee voltage of 0.2 V in the device configuration “glass/CZTS/CdS/Ag” was observed in the current voltage characteristics. The as-prepared and the vacuum-annealed p-n junction exhibited negative photosensitivity of magnitude 0.21 and 0.16 respectively. The air-annealed device structure exhibited photosensitivity of 216.

Physical properties of the low-cost CZTS absorber layer deposited by spin-coating: effect of the copper concentration associated with SCAPS-1D simulation.

Five samples of copper zinc tin sulfide (CZTS) thin films were deposited by a spin-coating technique at various copper concentrations ranging from 0.5 M to 2.5 M in steps of 0.5 M, in order to improve their stability, efficiency, performance, and reduce the production costs. The XRD patterns showed the existence of the three main characteristic peaks of CZTS (112), (220), and (312), which indicated the formation of the kesterite structure of CZTS. The gap energy of the thin films was calculated based on the derivation method using the absorbance data, and the values obtained varied from 1.46-1.58 eV for 0.5, 1, 1.5, 2, and 2.5 M copper molarity, respectively. Hall effect measurements were used to determine conductivity, which in turn increased with the concentration of copper in the films. The characterization results showed that the sample C3, which represents the 1.5 M copper concentration, exhibited higher crystallinity and better optical and electrical performance than the others. Finally, a theoretical efficiency of 11.6% was obtained when simulating the solar cell using the CZTS thin film (CZTS/ZnS/S:ZnO) in the SCAPS-1D simulation program using the parameters obtained in this study. Under the adopted synthesis conditions, the theoretical simulation corroborated the experimental findings, thus confirming that the synthesized material is a promising candidate for solar cell applications as an absorber layer.

Characterizations of extrinsically doped CZTS thin films for solar cell absorbers fabricated by sol-gel spin coating method

In copper zinc tin sulfide (CZTS) based thin films, copper zinc antisite (CuZn) represents the major p-type acceptor defect with low formation energy. This antisite can create defect-dominated carrier recombination hotspots, which reduces power conversion efficiency. Extrinsic doping in cationic sites of the CZTS thin film during synthesis is an effective way to passivate this defect. It has previously been reported that employing Cd as a dopant can passivate this defect and improve film quality. Injecting toxic Cd into non-toxic CZTS may create more problems than it solves. Simultaneous doping of Cd and other atoms like Mg is hypothesized to accomplish this goal of lowering Cd concentration. For this, it is important to know the effect of doping Cd and Mg separately under analogous experimental conditions. The structural, morphological, and optical properties, as well as the chemical bonding states, of sol-gel spin-coated CZTS thin films were investigated in this study using independent and controlled Cd and Mg doping. The fabrication procedure consisted of two steps: sol-gel spin coating followed by sulfurization. As a solvent for precursors in creating sols for spin coating processes, dimethyl sulfoxide (DMSO) was employed. Each dopant's precursor concentration was chosen to ensure an identical mole percentage of zinc precursor in the solution. The fabricated films were characterized undoped and doped forms using X-ray diffractometry (XRD) with Rietveld refinements, Raman spectroscopy, Field emission scanning electron microscopy (FESEM), 3D profilometry, and Ultraviolet-visible near-infrared (UV-Vis NIR) spectroscopy. The elemental composition ratio and chemical bonding states of the fabricated films were probed by Energy dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS), respectively. Fabricated thin films exhibit distinct synergistic features depending on the dopant types used in the fabrication process. The crystal structure of the doped absorber and the chemical valence states of the other elements (Cu, Zn, Sn, and S) were not changed as shown by XRD, Raman, and XPS analyses. The main diffraction peak at the (112) plane is found at Bragg's diffraction angle of 28.6° for an undoped sample. This peak shifts left upon Cd and Mg doping to 28.2° and 28.4° owing to different ionic radii of dopants relative to Zn ions, which indicates the presence of dopants in the fabricated films. Raman spectroscopy probes the Cu-Sn-S secondary phases: cubic Cu2SnS3 at 305 cm−1 in the undoped sample, tetragonal Cu2SnS3 at 296 cm−1 in the Cd-doped sample, and orthorhombic Cu3SnS4 at 291 cm−1 in the Mg-doped sample. From the EDS results, it appears that 45% of the Zn atoms in both the Cd-doped and Mg-doped samples are partially substituted by Cd and Mg, respectively. The optical band gap for Cd-doped samples decreases from 1.61 eV to 1.56 eV when compared to undoped samples. For Mg-doped samples, the optical band gap shrinks even more to 1.1 eV. This corresponds to shifting of absorbance spectra to higher wavelengths known as “redshift”. Urbach energy is determined to be 284 meV and 1072 meV for Cd and Mg doped samples, respectively, to address band tailing issues. Mg doping enhances crystallite size slightly while decreasing microstrain and dislocation density. The RMS surface roughness of Cd and Mg doped samples is 147 nm and 280 nm, respectively. Nevertheless, the primary peaks of Cu, Zn, Sn, S, Cd, Mg, and O, as well as the secondary photoelectron emission lines of these elements, are all found to be present and identified in both the doped samples. These results imply that Cd and Mg doping in the Zn-cationic site of virgin CZTS thin film can be regulated systematically to get appreciated features as a solar cell absorber.

Effect of Na Doping on Some Physical Properties of Chemically Sprayed CZTS Thin Films

In this work, sodium-doped copper zinc tin sulfide (CZTS) thin films are prepared by depositing them on glass substrates at temperature of (400±10) °C and thickness of (350±10) nm using Chemical Spray Pyrolysis (CSP) technique. 0.02 M of copper chloride dihydrate (CuCl2.2H2O), 0.01 M of zinc chloride (ZnCl2), 0.01 M of tin chloride dihydrate (SnCl2.2H2O), and 0.16 M of thiourea (SC(NH2)2) were used as sources of copper, zinc, tin, and sulphur ions respectively. Sodium chloride (NaCl) at different volumetric ratios of (1, 3, 5, 7 and 9) % was used as a dopant source. The solution is sprayed on glass substrates. XRD diffraction, Raman spectroscopy, FESEM, UV-Vis-NIR, and Hall effect techniques were used to investigate the structural, optical, and electrical properties of the produced films. The XRD diffraction results revealed that all films are polycrystalline, with a tetragonal structure and a preferential orientation along the (112) plane. The crystallite size of all films was estimated using Scherrer's method, and it was found that the crystallite size decreases as the doping ratio increases. The FESEM results revealed the existence of cauliflower-shaped nanoparticles. The optical energy band gap was demonstrated to have a value ranging from 1.6 to 1.51 eV with a high absorption coefficient (α ≥104 cm-1) in the visible region of the spectrum. Hall measurements showed that the conductivity of CZTS thin films with various Na doping ratios have p-type electrical conductivity, and it increases as the Na doping ratio increases.

Numerical Analysis of a CZTS Solar Cell with MoS2 as a Buffer Layer and Graphene as a Transparent Conducting Oxide Layer for Enhanced Cell Performance.

Copper zinc tin sulfide (CZTS) can be considered an important absorber layer material for utilization in thin film solar cell devices because of its non-toxic, earth abundance, and cost-effective properties. In this study, the effect of molybdenum disulfide (MoS2) as a buffer layer on the different parameters of CZTS-based solar cell devices was explored to design a highly efficient solar cell. While graphene is considered a transparent conducting oxide (TCO) layer for the superior quantum efficiency of CZTS thin film solar cells, MoS2 acts as a hole transport layer to offer electron–hole pair separation and an electron blocking layer to prevent recombination at the graphene/CZTS interface. This study proposed and analyzed a competent and economic CZTS solar cell structure (graphene/MoS2/CZTS/Ni) with MoS2 and graphene as the buffer and TCO layers, respectively, using the Solar Cell Capacitance Simulator (SCAPS)-1D. The proposed structure exhibited the following enhanced solar cell performance parameters: open-circuit voltage—0.8521 V, short-circuit current—25.3 mA cm−2, fill factor—84.76%, and efficiency—18.27%.

Structural and Optoelectronic Characterization of Synthesized Undoped CZTS and Cd-doped CZTS Thin Films

Copper zinc tin sulfide (CZTS) thin films with different doping ratios of Cadmium (Cd) were successfully fabricated using the sol-gel method by dip-coating technique. The surface morphology, the crystal structure properties as well the optical properties of undoped CZTS thin film and Cd- doped CZTS thin films were investigated using scanning electron microscopy (SEM), x-ray diffraction (XRD), and UV-Vis spectrophotometer. SEM micrographs demonstrated that the size and morphology of the particles improve due to increasing the Cd concentration in CZTS thin films. In addition, the XRD patterns exhibited the crystalline nature for CZTS thin films with kesterite crystal structure and showed improvement in some crystal structure properties such as crystal size and volume of unit cell with the incorporation of Cd into CZTS thin films. Moreover, optical bandgap energy

Optimization of the optoelectronic properties of copper zinc tin sulfide thin films for solar photovoltaic applications

Copper Zinc Tin Sulfide (CZTS), a successful contender for environmentallybenign thin film photovoltaics was successfully prepared on soda-lime glass substrates through an economically feasible nebulizer assisted spray pyrolysis technique. Further, a solar cell structure withn-CdS/p-CZTSheterojunction was fabricated to study the performance of the nebulizer sprayed CZTS absorber layer using different precursor solutions for copper such as copper acetate, copper chloride, and copper nitrate. Investigations were done to ascertain the influence of different copper precursors on the optoelectronic properties of CZTS thin films by systematically analyzing their characteristics determined by using different analytical techniques. X-ray diffraction studies show a preferential orientation along (112) plane for the deposited kesterite film. The obtained film thickness and crystallite size were found to be 507 nm and 8 nm, respectively, for the film derived from copper nitrate based spray solution. AFM morphological analysis also confirmed a higher particle size for copper nitrate based CZTS film whose band gap was found to be 1.50 eV. The absorption characteristic was also in the favor of nitrate form of the copper precursor which shows a higher absorption value in the visible region than the rest of the samples. Its carrier concentration was found to be 8.06 × 1017 cm−3 which is 4 times higher than the rest of the films and mobility was found to be of the order of 12.3 cm2 V−1 s−1. The open circuit voltage, short circuit current, fill factor, and efficiency of copper nitrate based CZTS solar cell structure was found to be better and is determined to be 0.27 V, 2.51 mA cm−2, 24.3%, and 0.165%.

Deposition of CZTS|ZnO Hetero-Junction Using SILAR and Spray Pyrolysis

Copper zinc tin sulphide (CZTS) thin films have been deposited on glass substrate at 323 ± 5 K using sequential ionic layer adsorption reaction (SILAR). The number of SILAR cycles required for optimum crystalline quality CZTS thin films was optimized. The as-deposited CZTS thin films showed kesterite crystalline structure with preferential orientation along (103) plane. Structural, optical, electrical, and morphological properties of the films changed when the as-prepared films were subjected to annealing in a vacuum chamber maintained at 3 × 10–4 Torr at temperatures of 473, 573, and 673 K. Film resistivity was found to decrease exponentially as the annealing temperature was increased. We have achieved a resistivity of 4.4 × 10–4 Ω m for the as-prepared thin film, which is lowest among SILAR-grown films at temperature lower than 373 K without any post-deposition processing. A superstrate-type p–n junction was fabricated by growing nano-structured zinc oxide (ZnO) on top of the glass|CZTS structure using chemical spray pyrolysis technique. The photosensitivity of the p–n junction was reversed when the structure was subjected to vacuum annealing at 673 K.

Surface-treated Cu2ZnSnS4 nanoflakes as Pt-free inexpensive and effective counter electrode in DSSC

Inexpensive semiconducting counter electrode (CE) was fabricated from copper zinc tin sulfide (CZTS) nanoflakes (NFs) through simple non-vacuum-based techniques. The kesterite CZTS NFs were synthesized by hot injection method using oleic acid as solvent. CZTS CE was prepared through solid-state ligand exchange method using ammonium sulfide salt ((NH4)2S) as the displacement ligand. Thin-film CZTS CE (on FTO substrate) was developed through inexpensive layer-by-layer (LbL) approach, without any post-treatment such as toxic sulfurization process. Hence, the fabrication of CZTS CE through this approach is scalable. The CZTS thin film showed NFs like morphology with higher surface area and achieved good electrocatalytic activity towards the reduction of iodide electrolyte. Two DSSCs using different CEs (CZTS NFs and Pt) were fabricated in separate cell structures in our laboratory. DSSC with CZTS NFs as CE showed the power conversion efficiency of 2.95% which is comparable to the DSSC with Pt (3.11%).

Investigation on the sulfurization temperature dependent phase and defect formation of sequentially evaporated Cu-rich CZTS thin films

We report synthesis of Copper Zinc Tin Sulfide (CZTS) thin films using sequential evaporation technique. The as-deposited films were subjected to various sulfurization temperatures ranging from 520 °C to 640 °C. This paper presents a detailed analysis of temperature dependent phase and defect formation in Cu-rich off-stoichiometric CZTS thin films. CZTS thin films moved from F-type to C-type with decreasing Cu/Zn disorder and defect concentration with increasing sulfurization temperature. The resulting films showed less off-stoichiometry in contrast to initial choice of intended off-stoichiometry exhibiting the structural flexibility within the compositional limits. Despite being off-stoichiometric, all the samples exhibited the tetragonal CZTS phase with preferred orientations. Raman analysis showed the disappearance and reappearance of secondary phases with increasing sulfurization temperature. EDS analysis suggested that composition of the films moved towards better stoichiometry till 580 °C before deteriorating again. Composition and lattice parameter values suggested Cu-rich off-stoichiometric nature of sulfurized CZTS thin films. AFM study showed dependence of roughness with sulfurization temperature. Band gap was obtained in the range of 1.28 eV to 1.48 eV from UV–Vis spectroscopy measurement. PL analysis revealed the asymmetric shape and blue shift of the peaks. Band-to-tail recombination becomes pronounced with increase in sulfurization temperature. XPS analysis showed elements are in expected oxidation states.

Investigations on post sulphurised Cu2ZnSnS4 absorber layer thin films prepared using radio frequency magnetron sputtering

Copper zinc tin sulfide (CZTS) quaternary semiconductor thin films were prepared using binary sulfur rich sputtering targets - copper sulfide (CuS), zinc sulfide (ZnS), and tin sulfide (SnS) by Radio Frequency Magnetron Sputtering with the stacking sequence CuS/ ZnS/ SnS at a substrate temperature of 300 °C. The films were then subsequently sulphurised at 350 °C in Hydrogen Sulfide atmosphere for 60 min. X-ray diffraction studies carried out on the CZTS films revealed the presence of CZTS kesterite phase along the 〈112〉 and 〈220〉 directions. X- ray diffraction results were validated by Raman spectroscopy. The composition of CZTS thin films were confirmed using X-Ray photoelectron spectroscopy and the atomic percentage of the individual elements were quantitatively estimated. The Valance band spectra and Ultra-violet photoelectron spectroscopy were used to study the electronic properties of the sulphurised CZTS thin films. The optical properties of CZTS thin films were studied using Ultraviolet - visible spectrophotometer and the optical band gap was found to be 1.477 eV. The Hall Effect measurements confirmed the p-type nature of the films and the results are discussed.

Current-voltage characteristics of Cu2ZnSnS4 absorber layer for energy harvesting devices

Environment friendly Copper-Zinc-Tin-Sulphide (CZTS)/Cadmium sulphide (CdS) thin film solar cells have been fabricated by sequential vacuum thermal evaporation technique. The developed CZTS films having the thickness of 1μm from layer by layer deposition of Cu: ZnS: Sn precursors having various compositional ratios (2:1:1, 2:1.5:1 and 2:2:1). Structural and morphological information of CZTS films were analyzed by XRD, Raman and SEM. The structural analysis showed increase with thickness and grain size increases whereas strain and dislocation density decreases. UV–vis absorption studies revealed that CZTS thin films have an optical band gap around 1.5 eV and it shows a large absorption coefficient (>104 cm−1). Four probe and Hall measurements indicate that CZTS thin film has the resistivity from 1.5–2.96 Ω-cm and the hole concentration from the value 9.1 × 1016–2.09 × 1018 N (cm−3). The deposited film CZTS were annealed at 500°C, to avoid forming binary compounds. Thin film solar cell has the structure of ITO/Mo/CZTS/CdS/i-ZnO/Al-grid/ITO exhibits the photovoltaic conversion efficiency of 5.6% under Air Mass (AM) 1.5 conditions and its photovoltaic performances were examined. This approach is favoured due to cell efficiency has a very large influence on the acceptable manufacturing cost of a PV module.

Structural and optical properties of CZTS nanoparticles prepared by a colloidal process

This research presents the influence of copper (Cu) concentration on the properties of copper zinc tin sulfide (CZTS) nanoparticles (NPs) synthesized by a colloidal method, employing oleylamine as an organic solvent. From the structural analysis, a pure phase of CZTS was obtained at an optimized molar ratio of 1.8:1.1:1:4, and secondary phases were observed as the Cu concentration increased. The increment of the NPs size from 15 to 50 nm was noticed as a function of Cu concentration. Importantly, the optical bandgap energy was tuned from 1.35 to 1.68 eV with respect to Cu concentration. The sample synthesized at the molar ratio of 1.8:1.1:1:4 showed a pure phase CZTS with desired elemental composition and bandgap. Furthermore, CZTS thin films were prepared by a doctor-blade method using synthesized NPs followed by annealing under a sulfur/nitrogen atmosphere. The annealed CZTS film showed a significant improvement in the morphological, electrical and optoelectronic properties. Thus, the annealed CZTS film can be efficiently used as an absorber layer in low-cost thin film solar cells. Synthesis of CZTS nanoparticles by hot injection process at different copper concentration and their impact on the particle size & bandgap.

Surface Characterisation of Spin Coated Quaternary Chalcogenide CZT(S, O) Thin Film for Optoelectronic Applications

Thin films of copper zinc tin sulphide (CZTS) have been deposited on glass substrate at various solution concentration and angular speed using sol-gel spin coating technique. Surface morphology showed that the deposited layers are continuous and pinhole free. The film’s particles are evenly distributed and adhered firmly to the substrates. X-ray diffraction studies revealed that the films are polycrystalline with tetragonal kesterite structure. Interplanar spacing and average crystallite size were estimated as 3.732 Å and 56.53 nm. Film’s thickness and stoichiometry were determined from Rutherford Backscattering Spectroscopy (RBS) as127 nm and Cu_1.5Zn_1.0Sn_1.1S_4.4O_3.3. Optical studies showed that the deposited films exhibit direct band transition. The values of the energy gap were found between 1.30 and 1.60 eV. The result of the study suggested that the deposited CZTS thin films can perform as a good absorber material in nanostructured optoelectronic devices.

Effect of defects and secondary phases in Cu2ZnSnS4 absorber material on the performance of Zn(O,S) buffered devices

Copper zinc tin sulfide (CZTS) absorber layer attracts so much attention in photovoltaic industry since it contains earth abundant, low cost and non-toxic elements contrary to other chalcogenide based solar cells. In the present work, CZTS absorber layers were prepared following a two-stage process: firstly, a stack of metal precursors (Copper (Cu)/Tin (Sn)/Zinc (Zn)/Copper (Cu)) were deposited on molybdenum (Mo) substrate by magnetron sputtering, then this stack was annealed under S atmosphere inside a tubular furnace. CZTS thin films were investigated using energy dispersive X-ray spectroscopy, X-ray diffraction, scanning electron microscopy and Raman spectroscopy. The effect of sulfurization time and the thickness of top and bottom Cu layer in precursors on the properties of CZTS thin films were investigated. The importance of Cu thickness adjacent to Sn to avoid detrimental phases was addressed. The significance of sulfurization time to restrict the Sn and Zn losses, formation of oxides such as tin dioxide and zinc oxide, and formation of molybdenum disulfide and voids between Mo/CZTS interface was also addressed. Moreover, cadmium sulfide buffer layer, which is conventionally used in CZTS solar cells, is replaced by an environmentally friendly alternative zinc oxysulfide buffer layer.

Optical and Electrical Properties of Copper Zinc Tin Sulfide Films As Solar Cell Absorber Materials Prepared by a Compacting Process

The copper zinc tin sulfide (CZTS) thin films are prepared by a promising non vacuum compacting process based on ball milling and coating technique. The results reveal that a well-formed crystalline structure of kesterite CZTS are observed after sintering at 450°C. The optical band gap is 1.49, 1.59, 1.33, and 1.21 eV for the films with Cu/Zn/Sn atomic radio of 1.00 : 0.50 : 0.52, 1.00 : 0.44 : 0.41, 1.00 : 0.60 : 0.49, and 1.00 : 0.49 : 0.58, respectively. The compacting process can further improve the performances of CZTS film. For the CZTS thin film with Cu/Zn/Sn atomic radio of 1.00 : 0.60 : 0.49, the surface morphology of the film is significantly improved by a compacting process applied to the coating films before sintering, and the resistivity decreased from 23.67 to 1.18 Ω cm with the compacting pressure increasing from 0 to 200 MPa at room temperature, which showing a promising application of the compacting process method in fabricating CZTS film for solar cells.