Cu2ZnSnS4 Thin Films Research Articles

Mapping the Energetics of Defect States in Cu2ZnSnS4 films and the Impact of Sb Doping.

The sub-bandgap levels associated with defect states in Cu2ZnSnS4 (CZTS) thin films are investigated by correlating the temperature dependence of the absorber photoluminescence (PL) with the device admittance spectroscopy. CZTS thin films are prepared by thermolysis of molecular precursors incorporating chloride salts of the cations and thiourea. Na and Sb are introduced as dopants in the precursor layers to assess their impact on Cu/Zn and Sn site disorder, respectively. Systematic analysis of PL spectra as a function of excitation power and temperature show that radiative recombination is dominated by quasi-donor–acceptor pairs (QDAP) with a maximum between 1.03 and 1.18 eV. It is noteworthy that Sb doping leads to a transition from localized to delocalized QDAP. The activation energies obtained associated with QDAP emission closely correlate with the activation energies of the admittance responses in a temperature range between 150 K and room temperature in films with or without added dopants. Admittance data of CZTS films with no added dopants also have a strong contribution from a deeper state associated with Sn disorder. The ensemble of PL and admittance data, in addition to energy-filtered photoemission of electron microscopy (EF-PEEM), shows a detailed picture of the distribution of sub-bandgap states in CZTS and the impact of doping on their energetics and device performance.

Enhancement of photoelectric properties of Cu2ZnSnS4 thin films by electronic excitations induced by swift heavy ions

The structural, optical, and current–voltage characteristics including photosensitivity of copper zinc tin sulphide (Cu2ZnSnS4) thin films were modified significantly by the electronic excitations. These excitations were induced by swift heavy ion (SHI) beams of 100 –120 MeV of O, Ag, and Au. X-ray diffraction patterns confirm that the pristine and irradiated films crystallize in kesterite structure and the crystallite size increases after O, and Ag ion irradiations compared to Au ions. The micro-Raman spectra reveal the presence of lattice defects in the Au irradiated sample. The analysis shows that the crystallinity of the Cu2ZnSnS4 thin film increases with O ion irradiation indicating that the density of defect states decreases after SHI irradiation. The maximum photosensitivity is found to be 62% for O irradiated thin films compared to other ion beams due to the reduction in the band gap.

Structural, optical and electrical properties of Cu2ZnSnS4 thin film deposited by electron beam evaporation method

In this research work, the Cu2ZnSnS4 (CZTS) powder was synthesized using microwave-assisted technique. Sandwich device of Al/ CZTS /Al thin film was deposited by electron beam gun evaporation method (EBG). The optical and structural properties of CZTS have been investigated using UV–visible optical absorption, scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. The XRD pattern confirmed the formation of kesterite structure for CZTS. SEM micrograph revealed the crystalline and porous surface characteristic of CZTS thin film. The CZTS particles have band gap energy 1.6 eV that was determined by UV–visible. In order to specify the dominant conduction mechanism, AC conductivity of CZTS thin film was measured at different temperatures and frequencies (290 K<T < 410 K and 102 Hz <f< 105 Hz). At the temperature range from 290 K to 410 K for 104 Hz <f< 105 Hz, hopping is the dominant conduction. The exponent s values (from 0.67 to 0.86) confirm the hopping mechanism in accordance with Jonscher law, also.

Characterization of Cu2ZnSnS4 thin films prepared with and without thin Al2O3 barrier layer

We investigated the effect of thin Al2O3 barrier layer (∼20 nm) deposited by radio frequency magnetron sputtering technique on the structural, morphological, optical, and electrical properties of Cu2ZnSnS4 (CZTS) films. Major differences in the crystalline qualities of the films were not observed with the addition of the Al2O3 layer except for a small decrease in crystallite size. Raman spectra of the film with the Al2O3 layer exhibited the peaks belonging to ZnS and Cu2-xS secondary phases. X-ray photoelectron spectroscopy analysis showed that SO42- and CuSO4 compounds were formed on the surfaces of the films. The formation of the CuSO4 phase was associated with the bonding between CuO and S in an oxidized CZTS surface. The presence of the ZnS, Cu2-xS secondary phases, and CuSO4 on the surfaces of the films were also confirmed by scanning electron microscopy images. The film with the Al2O3 layer differed from the other films with its surface that have randomly distributed porous-structured agglomerations and a decrease in the ZnS secondary phases on its surface. All films exhibited different Na distributions in secondary ion mass spectroscopy depth profiles. The Al2O3 layer caused a slower gradient in Na diffusion with decreasing the accumulation of Na element at a distinct region. The activation energy for the thermally activated band conduction was calculated as 0.030 eV and attributed to the thermal release of the holes from the vacancy of copper (VCu) defect states. The results of temperature-dependent conductivity measurements indicated that there were different conduction mechanisms in the films.

Inhibiting the formation of MoS2 between Cu2ZnSnS4 thin film and Mo(211) foil substrate by inserting a Mo(110) intermediate layer

In Cu2ZnSnS4 (CZTS) thin film solar cells, a MoS2 layer is often found at the CZTS/Mo interface, which limits the photovoltaic performances of solar cells. In this work, a Mo (110) intermediate layer was inserted between the CZTS thin film and Mo (221) foil substrate to inhibit the formation of MoS2 layer. The experimental results showed that a MoS2 layer with a thickness of 2.0 μm was observed at the CZTS/Mo foil interface without Mo intermediate layer. After the insertion of a sputtered Mo (110) intermediate layer between CZTS and Mo foil substrate, the thickness of MoS2 reduced as the thickness of Mo intermediate layer increased. The MoS2 interface layer can not be detected from the cross-sectional SEM images when the thickness of Mo intermediate layer exceeded 277 nm. The inhibition of MoS2 was considered to be due to the chemical inertness of Mo (110) during sulfurization. The ohmic contact characteristic of CZTS/Mo foil was improved when the Mo layer had a suitable thickness. Therefore, the interface properties between CZTS and Mo (221) foil can be enhanced by using a Mo (110) intermediate layer.

Influence of sulfurization time and Cu-ZnS-Sn stack order on the properties of thermally evaporated CZTS thin films

Cu2ZnSnS4 (CZTS) thin films were synthesized in a two-step procedure. Sulfurization of stacked thin films SLG/ZnS/Sn/Cu (S1) and SLG/Cu/Sn/ZnS (S2) after sequential deposition of Cu, ZnS, and Sn precursors was carried out. At 550 °C, two sulfurization periods were applied to both stack orders. Sample S1 sulfurized for 30 min (S1-T30) had a better crystallite size of roughly 50 nm, lower lattice strain, and lower dislocation density than other samples. The Cu/Zn cation ordering in the CZTS crystal system was significantly affected by stack sequence and sulfurization time, according to Q-factor calculation. The stack order of the S1 series allowed for homogenous and distinct particle development. From the elemental analysis, it is observed that the stack sequence and sulfurization used for sample S1-T30 permitted a near stoichiometric composition. The sample S1-T30 exhibited an optimal band gap value of 1.47 eV. To propose feasible alterations in the structural ordering, band gap calculations were used. In comparison to the stack order of the S2 series, the stack order SLG/ZnS/Sn/Cu with a sulfurization time of 30 min created a single-phase CZTS, implying less synthesis time to obtain an absorber quality CZTS layer for solar photovoltaic application.

Photovoltaic performance of Cu2ZnSnS4 thin film solar cells on flexible molybdenum foil formed by electrodeposition and sulfurization

Photovoltaic performance of Cu2ZnSnS4 thin film solar cells on flexible molybdenum foil formed by electrodeposition and sulfurization

Improvement of hetero-interface engineering by partial substitution of Zn in Cu2ZnSnS4-based solar cells

This paper investigates the effects of partial substitution of zinc (Zn) in pure sulfide kesterite (Cu2ZnSnS4) by cadmium (Cd) and manganese (Mn) incorporation. Thin films of Cu2ZnSnS4 (CZTS), Cu2Zn1–xCdxSnS4 (CCZTS) and Cu2Zn1–xMnxSnS4(CMZTS) were produced chemically. A comparison of pure CZTS with CCZTS and CMZTS was performed to study the influence of Cd and Mn incorporation on the morphology, structure, optical and electronic properties of the films. The results show an improvement of the morphology and an adjustment of the band gap and valence band position by partial substitution of Zn with Cd and Mn. In addition, for the first time, the band alignment at the absorber/buffer hetero-interface is studied with partial Zn substitution. Band alignments at the absorber/buffer hetero-interface were estimated by XPS and UV/Visible measurements. The results show a cliff-like CBO for CZTS/CdS heterojunction, a spike-like CBO for CCZTS/CdS and a near flat-band CBO for CMZTS/CdS heterojunction.

Effects of incorporation of Ag into a kesterite Cu2ZnSnS4 thin film on its photoelectrochemical properties for water reduction.

Kesterite Cu2ZnSnS4 (CZTS) thin films in which the Cu site was partially replaced with Ag were prepared by spray deposition on an Mo-coated glass substrate. Successful replacement of Cu components in the CZTS lattice with Ag up to an Ag/(Cu + Ag) ratio of 0.20 was achieved. Samples with relatively low contents of Ag (Ag/(Cu + Ag) ratios of 0.05 and 0.10) showed obvious grain growth compared to that of bare CZTS, whereas samples with higher Ag contents showed an appreciable decrease in grain sizes. Photoelectrochemical properties for water reduction (H2 production), which was examined after surface modifications with an In2S3/CdS double layer and Pt catalyst for H2 evolution, depended strongly on such morphological differences; a maximum conversion efficiency, i.e., half-cell solar to hydrogen efficiency, of 2.4% was achieved by the photocathode based on the film with an Ag/(Cu + Ag) ratio of 0.10. Minority carrier dynamics examined by photoluminescence measurements indicated that such an active sample of PEC H2 production had a relatively long carrier lifetime, suggesting that the suppression of carrier recombination at grain boundaries in the bulk of these kesterite films is one of the important factors for enhancing PEC functions.

Deposition of Cu2znsns4 Thin Film at Different Solution Flow Rates

Deposition of Cu2znsns4 Thin Film at Different Solution Flow Rates

On the Deposition and Characterization of Cu2znsns4 Thin Films and Fabrication of Cadmium Free Heterojunction Solar Cells

On the Deposition and Characterization of Cu2znsns4 Thin Films and Fabrication of Cadmium Free Heterojunction Solar Cells

Computational and experimental characterizations of annealed Cu2ZnSnS4 thin films

We report on the synthesis and characterization of Cu2ZnSnS4 (CZTS) thin films prepared at different annealing temperatures using the sol-gel method and deposited on glass substrates using the immersing method. The XRD analysis demonstrates that the films annealed at 450 °C exhibit the most stable tetrahedral kesterite structure. Computationally, the Vienna ab initio simulation package (VASP) has been implemented to calculate critical structural properties of as-prepared CZTS) thin films and compared with those extracted from the XRD patterns. An excellent agreement is obtained between the calculated and measured structural parameters. Optical measurement of key optical parameters of annealed CZTS thin films shows a drastic manipulation of all-optical properties compared to the as-prepared thin films. In particular, an optical band gap of 1.62 eV obtained for annealed CZTS thin films at 450 °C makes them eligible to be potential candidates for thin film-based high-efficiency solar cells. Calculations of elastic properties of annealed thin films reveal that crystallite size increases and microstrain decrease compared with those of as-prepared thin films. The sheet resistance of annealed CZTS thin films exhibits a significant decline as the annealing temperature is increased. The electrical properties of annealed CZTS thin films could match some conductors. Remarkably, at 450 °C annealing temperature, the sheet resistance decreases to 74 Ω.cm−1 indicating the possibility of using the annealed CZTS thin films for efficient and low cost solar cell applications.

Properties of Cu2ZnSnS4 films obtained by sulfurization under different sulfur-vapor pressures in a sealed ambient

Thin-films of Cu2ZnSnS4 (CZTS), a promising photoabsorber for photovoltaics, were obtained by sulfurization of the precursor films at 550 °C in evacuated and sealed quartz ampoules under various partial pressures (22.3–232.5 kPa) of sulfur-vapor, and its effects on the morphological and optical properties were studied. The precursor films were obtained on the molybdenum (Mo) coated soda-lime glass substrate via solution-chemistry. The observed changes in the morphology have been explained based on the amount of CuS formed and its conversion to sulfur-poor Cu2S. A decrease in the grain size from 448 to 223 nm was observed with the increase in partial pressure of sulfur-vapor. The thickness of the molybdenum sulfide (MoS2) layer that forms at the CZTS – Mo interface during sulfurization, increased from 62 to 479 nm. The structural disorder, estimated using Raman spectroscopy, increased with the increase in the partial pressure of sulfur-vapor.

The impact of precursor thickness and surface roughness on the power factor of Cu2ZnSnS4 (CZTS) at near room temperature: Spin-coating deposition

This work investigated the thermoelectric properties of Cu2ZnSnS4 (CZTS) thin films deposited on the soda-lime glass using spin-coating techniques with different layers. X-ray diffraction (XRD) pattern confirms the increase of the layer number leads to improve the crystallite size and all the films exhibit tetragonal structure with the presence of secondary phases. EDX shows a reduction of Cu and Zn contents while an increase in Sn contents is observed when the thickness increases. Surface topography is also carried out to study the surface roughness and it is found to be minimum when we deposit 4 layers. The absorption spectra show that CZTS exhibit a bandgap varied between 1.33 and 1.9 eV, the resistivity and the Seebeck coefficient have been found to increase with the increase of surface roughness. This investigation indicates that Cu2ZnSnS4 thin films can be a suitable material for thermoelectric application at near room temperature range.

Effect of heating rate and precursor composition on secondary phase formation during Cu2ZnSnS4 thin film growth and its properties

Cu2ZnSnS4 (CZTS) as an absorber material has proven its potential for high efficiency solar cells. However, commercial viability for low cost photovoltaic depends on improving its efficiency beyond the existing values which require an understanding of secondary phase formation. In this work, CZTS layer of up to one micron thickness is prepared by sulfurization (annealing in the sulfur environment) of a precursor prepared using magnetron co-sputtering of Cu, Zn and Sn on soda lime glass. Precursor composition during co-sputtering and heating rate of the sulfurization process were varied to study its effect on secondary phase formation during CZTS growth. Characterization techniques like X-ray diffraction, Raman spectroscopy and UV-Vis spectroscopy were used to detect the phases formed in the film. Scanning electron microscopy and energy dispersive x-ray spectroscopy were performed to estimate the elemental composition and its distribution in the film. The studies and the results obtained therein bring out the impact of heating rate on the grain size. Simultaneously the secondary phase formation is found to be affected more by precursor composition than the heating rate. Raman measurements and bandgap estimation from UV-visible absorption spectra indicated the formation of ZnS in the film. The study showed the possibility to completely avoid the formation of both copper sulfide (CuS, Cu2S, etc.) as well as ZnS secondary phases under certain combination of process parameters.

Effect of RF sputter power on deposition of CZTX (X[dbnd]S, Se) active layer without selenization/sulfurization, for solar cell applications

Copper Zinc Tin Selenide Cu2ZnSnSe4 (CZTSe) and Copper Zinc Tin Sulfide Cu2ZnSnS4 (CZTS) thin films were deposited from a multicomponent single target with different RF sputter powers and a constant annealing temperature of 450°C. One step deposition with in-situ annealing was performed in order to avoid the individual metal losses during the process. Effects of various deposition parameters were investigated to finely control the elemental ratio of the quaternary target which in-turn helps to obtain the desired stoichiometry suitable for solar absorber materials as confirmed from EDS analysis. The phase purity of thin films was investigated and confirmed using XRD and Raman spectroscopy. A thin film solar cell device with n-CdS, ZnO, ZnO:Al layers and Al grids over the prepared kesterite CZTX (X = S, Se) films were deposited on Mo coated soda lime glass using complete vacuum deposition technique. Even though the optical, electrical and structural results are promising, the conversion efficiency for these single step processed CZTSe and CZTS solar cell devices were limited to 3.72% and 2.6% due to possible interface effect and smaller grain size of the deposited films. Considering the industrial fabrication of kesterite thin film solar cells, this processes assures an environmental friendly approach with inherent purity leading to one-step reduction in the mass production process.

Growth of Cu2ZnSnS4 thin film absorber layer on transparent conductive oxides and molybdenum substrates by electrodeposition for photovoltaic application

Cu2ZnSnS4 (CZTS) absorber layer for the photovoltaic application was successfully deposited on different substrates, indium tin oxide (ITO), fluorine-doped tin oxide (FTO) and molybdenum (Mo) using a single step electrodeposition process. The structural, morphological and optical properties of the CZTS films were analyzed by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), and photoluminescence (PL). The present study was designed to determine the effect of the substrate on the kesterite thin film properties grown by electrodeposition. The results confirm that the CZTS properties depend on the substrate nature. Furthermore, the CZTS films deposited on Mo substrate was found more appropriate for CZTS based solar cells due to their crystallinity and good morphology as well as their suitable energy bandgap around 1.6 eV.

Near-optimal composition of CZTS thin film via exploration of copper and thiourea molar concentration in spray pyrolysis technique

Attaining the optimal composition of Cu2ZnSnS4 (CZTS) thin film is a pre-requisite for photovoltaic application. Herein, the near-optimal composition of spray pyrolyzed CZTS thin film has been obtained by varying copper and thiourea molar concentrations in the precursor solution. Different characterization techniques such as x-ray diffraction (XRD), UV–vis spectroscopy, Scanning electron microscopy (SEM) and Energy-dispersive x-ray spectroscopy (EDS) have been employed to determine the changes in absorber layer properties. The CZTS thin films synthesized using Cu-0.016 M exhibits higher crystallinity with the direct band gap of 1.52 eV. Apart from that, the reduction of copper molar concentration in precursor solution minimizes the segregation of surface secondary phase. The variation of thiourea molar concentration facilities the growth of CZTS and reduces the formation of secondary phases. Besides that, the optical studies revealed that the increment in thiourea molar concentration leads to a broadening of band gap from 1.52 eV to 1.61 eV. The CZTS thin films synthesized using copper and thiourea molar concentrations of 0.016 M and 0.12 M showed appropriate absorber layer properties with near-optimal Cu-poor and Zn-rich ratio i.e., Cu/(Zn+Sn) = 0.81 and Zn/Sn = 1.26.

Suppressing the secondary phases via N2 preheating of Cu2ZnSnS4 thin films with the addition of oleylamine and/or 1-Dodecanethiol solvents

The demand for a reliable alternative renewable energy is skyrocketing given the detrimental effect of conventional energy sources on the environment and its rapidly depleting global supply. While Cu2ZnSnS4 (CZTS)-based photovoltaic devices have gained a foothold through enhanced energy conversion efficiency, efforts are still required to further boost the physical and chemical properties of the material for higher conversion efficiency. In this study, the impact of solvent addition on the purity of nitrogen (N2) preheating of CZTS ink formulations via the hot injection method was investigated. The CZTS inks were deposited using the spin coating technique and preheated at 150 °C under ambient N2 and then heated within the sulfurization process at 580 °C. Three types of CZTS samples were prepared comprising sulfur only, sulfur and Oleylamine (OLA), and 1-Dodecanethiol (1-DDT) dissolved in sulfur and OLA. Following the preparation of the CZTS thin films, the microstructural, vibrational, optical, and electrical properties of the thin films were performed via various analyses, including X-ray Diffraction (XRD) and Raman spectroscopy, Hall measurement, spectrophotometry, and Scanning Electron Microscope (SEM). Based on the results, the XRD patterns confirmed the formation of CZTS compounds with varying crystallite sizes, whereas the Raman analysis demonstrated that the synthesized films were composed of pure stannite phase CZTS. In addition, the sample ink with sulfur only exhibited a high crystallite size of 49 nm compared to 40 nm in the presence of OLA. Furthermore, a suitable bandgap for solar cells absorption was obtained in all samples. According to the electrical characteristics, all the p-type semiconductor samples recorded a low resistivity in the presence of 1-DDT and OLA. Overall, the sulfur/OLA/1-DDT sample demonstrated superior characteristics compared to the other materials based on its ideal surface morphology, high crystallite size, and low charge carrier concentration. The results presented in this paper demonstrated a promising approach for the synthesis of effective absorber thin films for photovoltaic applications.

Effect of Zn on nanoscale quaternary Cu2ZnSnS4 thin film electrodes for high performance supercapacitors

Nanostructured Cu2ZnSnS4 thin films have been deposited with different Zn concentrations by successive ionic layer adsorption and reaction (SILAR) method. The powder X-ray diffraction patterns have been confirmed the tetragonal structure of the Cu2ZnSnS4 film with the presence of wurtzite and kesterite phase. Scanning electron microscope attached with energy dispersive X-ray analyzer (EDX) has used to identify the existence of spherical morphology and confirmed the elemental composition present in the prepared films. The uniform distribution and rough surface of the film have been confirmed by atomic force microscopic (AFM) images. Tauc's plot have plotted and used to calculate the optical band gap of the films. The band gap obtained between 1.47 and 1.92 eV for different zinc concentrations. The optimized film has been examined by photo-electrochemical technique and the efficiency obtained as 1.678%. The electrochemical performances such as cyclic voltammetry, Galvanostatic charge-discharge and electrical impedance spectroscopy have been analyzed using the optimized film as a working electrode. This study resulted in maximum specific capacitance as 165.04 F g−1 at the current density 1 A g−1.