CTS Films Research Articles

The evolution of the crystallinity depending on the annealing temperature in the CTS films obtained by spray pyrolysis

We report the effect of temperature annealing with nitrogen atmosphere in the CTS film deposited by spray pyrolysis, and their evolution in crystallinity, as well as the contribution in the optical parameters, such as optical absorption coefficient, band gap, and the contribution in morphology. We could obtain the Cu4Sn7S16 and Cu2SnS3 proving with the XRD diffractograms and Raman analysis. The films showed a good crystallinity, and crystallite size between 11.9 nm and 18.1 nm. The optical absorption coefficient is ∼105 cm−1 and the band gap is between 0.86 eV and 0.95 eV. The band gap showed dependence on CTS phase. The morphology of the samples is like petals. The sample that has the best characteristics to be applied as absorber film on photovoltaic devices is the sample C10T1-245 (0.1 M (SnCl2 · 2H2O), 0.1 M (CuCl2 · 2H2O), 0.3 M (CS(NH2)2) with temperature annealing of 245 °C.

Ternary Cu2SnS3 Thin Films Deposited by Fully Controlled System of Spray Pyrolysis

A fully computerized system of spray pyrolysis was employed for fabricating copper tin sulphite ternary thin film onto glass substrates. During deposition process, the glass substrate was maintained at 310 ± 10 °C. After dissolving the raw chemicals, a mixture of their aqueous solutions was used for spraying process. The optimum solution mixture at the volumetric ratio [S/(Cu+Sn)=1] at 1.5 of pH. XRD investigation was approved a monoclinic phase of CTS. A number of different platform speed was tested in the deposition process. XRD diffraction peaks were described at 2θ = 28.39°, 33.02°, 47.34°, and 56.39° corresponding to the and , respectively. These are crystal planes of monoclinic copper tin sulphide. The FTIR study certified a number of the chemical bond of Cu-, Sn- and S-. The grain size was observed in the range of nano using Scherrer formula. Studying surface morphology of CTS films reveals a uniform coating on the substrates which approved by SEM investigations.

Antimony induced crystal growth for large-grained Cu2SnS3 thin films for photovoltaics

Nowadays, Cu2SnS3 is emerging as a promising solar cell material because of its suitable optoelectronic properties. Large-grained Cu2SnS3 thin films are highly desirable to realize high efficiency in Cu2SnS3-based solar cells. The deliberate addition of impurities into the absorber is an appropriate approach to fabricate large-grained absorber layers. Hence, we have doped a pentavalent antimony (Sb) into Cu2SnS3 films via chemical bath deposition of SnS/Sb2S3/CuS stacks followed by annealing in a graphite box. The effects of annealing temperature and annealing duration on the grain growth of Sb-doped CTS films is discussed in detail. Owing to its surfactant property, Sb-doping promotes a layer-by-layer growth mode and results in uniform, compact, and large-grained Cu2SnS3 films with grain sizes of 5 μm. Thus, Sb-doping assisted the crystal growth, to produce large-grained Cu2SnS3 thin films, which can provide a new path-way to enhance the device efficiency of Cu2SnS3-based solar cells.

The effect of different Cu/Sn ratios on the properties of monoclinic Cu2SnS3 thin films and solar cells fabricated by the sol–gel method

Ternary Cu2SnS3 (CTS) is a promising material for thin-film solar cells because it consists of nontoxic and earth-abundant elements. The present paper reports the preparation of monoclinic CTS thin films by a sol–gel solution-based method. The effects of the Cu/Sn atomic ratio on the structure and morphology were investigated. As the atomic ratio of Cu/Sn varied from 1.6 to 2.0, the compactness of the CTS films improved; furthermore, secondary phases, such as SnS, gradually disappeared; and the grain size of the films decreased. The CTS film with a Cu/Sn ratio of 1.9 showed a monoclinic structure with homogeneous morphology and a band gap of 1.12 eV, yielding a power conversion efficiency of 0.58%. These results could pave the way for the development of CTS thin-film solar cells.

Investigation of Laser Grooving Process on Copper Tin Sulfite Thin Films

Spray pyrolysis deposition has been successfully applied to fabricate CTS thin films onto glass substrates that maintained at 300°C, via the homemade fully computerized system. A mixture aqueous solution of thiourea and dihydrate chloride of Sn (II) and Cu (II) were used for the spraying process. Structural, optical, and morphological properties of CTS films were examined. XRD endorses a monoclinic crystallinity. XRD pattern has diffraction peaks at 2θ = 28.39°, 33.02°, 47.34° and 56.39°, respectively. The FTIR examination certified the vibration mode of Cu-S and Sn-S bonds. The crystallite size was noted about 78 nm, where measured by debye-Scherrer’s formula. Both absorption and transmission spectra were recorded in the wavelength range of 300-800 nm. The surface morphology of the fabricated CTS films exposed a uniform coating on the substrate with an applicable distribution. Laser grooving process was applied to grove the fabricated film. The groove width was found about 37 μm, etched via 500 mW blue laser source.

Fabrication of Cu2SnS3 thin film solar cells by sulphurization of sequentially sputtered Sn/CuSn metallic stacked precursors

In this present work, we report a novel fabrication technique of ternary Cu2SnS3 (CTS) thin films by sulphurization of sequentially sputtered Sn/CuSn (elemental/alloy) stacked metallic precursors. The focal aim of our investigation is on the impact of metallic precursors’ Cu/Sn ratio on the overall material properties of CTS films, which in turn, influence the photovoltaic device performance. All CTSs exhibited polycrystalline films with a mixture monoclinic CTS and orthorhombic SnS compound, p-type conductivity, and optical band gap in the range of 0.84–0.90 eV. Metallic precursor with Cu/Sn ratio of 1.09 produced optimum CTS film with post-sulphurization Cu/Sn ratio of 1.98 and highest conversion efficiency of 0.71%, respectively, despite exhibiting pronounced formation of SnS secondary phase. The correlation between XRD, Raman, and SEM-EDX outcomes revealed that CTS films from metallic precursors with Cu/Sn ratio higher than 1.09 undergo severe microstructural degradation due to Sn-loss through decomposition of volatile SnS phase and consequently, resulted in poorer absorber layer quality and lower device performance. Finally, several efficiency impeding factors are discussed and practical propostions to overcome them are presented.

Electrical properties modulation in spray pyrolysed Cu2SnS3 thin films through variation of copper precursor concentration for photovoltaic application

Thin film of Cu2SnS3 (CTS), a truly inexpensive photovoltaic absorber is deposited by low cost and non-vacuum spray pyrolysis technique on glass substrates. As deposited CTS films are of p-type in nature, however they are characterised with undesirably high free carrier concentration which leads to a large amount of recombination. Such a high carrier concentration is successfully reduced from 1020 cm−3 to the order of 1018 cm−3 by varying the initial molar copper concentration in the precursor solution. A combined XRD and Raman spectroscopy analysis reveals that the coexistence of secondary Cu3SnS4 phase is responsible for the higher carrier concentration of the order of 1021 cm−3, due to its semi-metallic nature. The optical study of the film also shows the reduction in the band gap from 1.73 eV to 1.29 eV with the absorption coefficient of >104 cm-1. These features of the precursor optimised CTS film enable it as a promising photovoltaic absorber.

Effects of different precursors on Cu2SnS3 thin film solar cells prepared by sputtering method

In this work, the impacts of different precursors on Cu2SnS3 thin film solar cells were investigated in detail. The two kinds of precursors of CuS/Sn and Cu/Sn were deposited on Mo-coated soda lime glasses by magnetron sputtering. Cu2SnS3 (CTS) films based on different precursors were fabricated by soft annealing and following sulfurization in S vapor. The crystal structure, phase purity, composition, surface morphology and cross section images of CTS films from different precursors were characterized by X-ray diffraction (XRD), Raman spectroscopy, energy dispersive spectrometry (EDS) and scanning electron microscope (SEM) respectively. Meanwhile, the optical-electrical properties of CTS thin films were detected by using UV–vis–INR Spectrophotometer and Hall measurement. As a result, the CTS thin films with smooth surface and uniform compositional ratio distribution were obtained from the precursors of CuS/Sn. The best conversion efficiency of the fabricated CTS film solar cell based on CuS/Sn precursors was 1.18% with a high open-circuit voltage of 299 mV.

Inexpensive Cu2SnS3 grown by room-temperature aqueous bath electrodeposition for thin film solar cells

We report the growth of Cu2SnS3 (CTS) thin films on F-doped SnO2 (FTO) glass substrates at room-temperature by low-cost electrodeposition technique using an aqueous medium without the evolution of hydrogen. Electrolyte concentration and deposition potential were optimized under the limits of water hydrolysis. As-deposited films are post-annealed in the presence of the sulphur flakes to establish the stoichiometry. The annealed films were found to contain high phase purity and favorable optical properties to be useful for the photovoltaic applications. Optical data reveal that the CTS films have direct optical bandgap of 1.25 eV with an absorption coefficient of the order of 104 cm[Formula: see text]. A photovoltaic cell architecture of Glass/FTO (back contact)/CTS/CdS/Al:ZnO/Al (front contact) exhibited an open circuit voltage of 28 mV, a short circuit current density of 8.4 [Formula: see text]A/cm2 and the fill factor of 25%. The absorber thickness optimization and the use of Mo-coated glass as a back contact improve the solar cell parameters. A further study in this aspect is under way.

Sulfurization temperature dependent physical properties of Cu2SnS3 films grown by a two-stage process

Cu2SnS3 (CTS) is a promising absorber for thin film solar cells because of its suitable opto-electronic properties. This article reports the effect of sulfurization temperature (Ts) on the physical properties of CTS thin films deposited by two-stage process. X-ray diffraction and Raman analyses revealed that sulfurized CTS films exhibited different polymorphic forms, such as triclinic structure (at Ts = 350 °C), tetragonal structure (at Ts = 400 °C), and monoclinic structure (at Ts = 450 °C). A phase change from monoclinic CTS to orthorhombic Cu3SnS4 was observed at Ts = 500 °C. The AFM results confirmed that the sulfurized films had the smooth surface without pinholes. The optical band gap was varied in the range, 2.34–1.49 eV with increasing sulfurization temperature from 150 °C to 500 °C. All the sulfurized films showed p-type conducting nature. The obtained results indicated that single phase CTS films prepared in the temperature range of 400–450 °C could be used as an absorber layer for the application of thin film solar cells.

Fabrication of high quality Cu2SnS3 thin film solar cell with 1.12% power conversion efficiency obtain by low cost environment friendly sol-gel technique

Cu2SnS3 (CTS) is an emerging ternery chalcogenide material with great potential application in thin film solar cells. We present here high quality Cu2SnS3 thin films using a facile spin coating method. The as deposited films of CTS were sulphurized in a graphite box using tubular furnace at 520 °C for 60 min at the rate of 2.83 °C min−1 in argon atmosphere. X-ray diffraction (XRD) and Raman spectroscopy studies confirm tetragonal phase and absence of any secondary phase in sulphurized CTS thin films. X-ray photoelectron spectroscopy (XPS) demonstrates that Cu and Sn are in +1 and +4 oxidation state respectively. Surface morphology of CTS films were analyzed by field emission scanning electron microscope and atomic force microscope (AFM), which revealed a smooth surface with roughness (RMS) of 6.32 nm for sulphurized CTS film. Hall measurements confirmed p-type conductivity with hole concentartion of sulphurized CTS thin film is of 6.5348 × 1020 cm−3. UV–vis spectra revealed a direct energy band gap varies from 1.45 eV to 1.01 eV for as-deposited and sulphurized CTS thin film respectively. Such band gap values are optimum for semiconductor material as an absorber layer of thin film solar cell. The CTS thin film solar cell had following structure: SLG/FTO/ZnO/CTS/Al with short circuit current density of (Jsc) of 11.6 mA cm−2, open circuit voltage (Voc) of 0.276 V, active area of 0.16 cm2, fill factor (FF) of 35% and power conversion efficiency of 1.12% under AM 1.5 (100 mW cm−2) illumination in simulated standard test conditions.

Fabrication of $$\text {Cu}_{2}\text {SnS}_{3}$$ Cu 2 SnS 3 films by annealing chemically deposited SnS–CuS precursors in a graphite box

Monoclinic $$\text {Cu}_{2}\text {SnS}_{3}$$ (CTS) thin films are prepared by annealing chemically deposited SnS–CuS precursors at 520-580 $$^{\circ }\text {C}$$ in a graphite box under atmospheric ( $$\text {N}_{2}+\text {S}_{2}$$ ) pressure, and the effects of annealing temperature and time on the grain growth and morphology of the films are investigated. The films prepared at 520 and 550 $$^{\circ }{\text{C }}$$ show improvement in grain size and the formation of uniform and compact grains with increasing annealing time. The films prepared at 580 $$^{\circ }\text {C}$$ exhibit good grain growth with grain sizes $$\sim 1.0{-}3.0\,\upmu \text {m}$$ ; however, the grain size does not increase with annealing time. Further, annealing time of 120 min at 550 and 580 $$^{\circ }\text {C}$$ leads to material loss. A small amount of $$\text {Cu}_{4}\text {SnS}_{4}$$ is detected in the films. In addition, annealing the films at 550 and 580 $$^{\circ }\text {C}$$ for 90 min with decreased CuS thickness results in a reduction of $$\text {Cu}_{4}\text {SnS}_{4}$$ phase, homogeneous grain growth with grain sizes of $$2.0{-}3.5\,\upmu \text {m}$$ throughout the film thickness, and hole mobilities in the range of $$6.0{-}5.3\,\text {cm}^{2}\,\text {V}^{-1}\,\text {s}^{-1}$$ . These results demonstrate the effectiveness of this annealing approach for producing high quality CTS films with micron-sized grains, which is useful for improving the efficiency of CTS-based thin film solar cells.

Cu2SnS3 thin film: Structural, morphological, optical and photoelectrochemical studies

Cu2SnS3 (CTS) thin film has been successfully deposited on the cost effective stainless steel substrate by simple and inexpensive chemical bath deposition method. The film is studied in term of their structural, morphological, optical and photoelectrochemical properties. The XRD study shows that CTS films consists a nanocrystalline structure with triclinic phase Raman analysis confirms the formation of CTS compound thin film. The SEM images show small crystallite grains of CTS material. The optical absorption study shows that the films have direct transitions with band gap energies of 1.35 eV. Moreover, the photoconversion efficiency of CTS thin film-based photoelectrochemical cell (PEC) is studied and found 0.12% efficiency.

Photoelectrochemical (PEC) studies on Cu2SnS3 (CTS) thin films deposited by chemical bath deposition method

Cu2SnS3 (CTS) thin films have been successfully deposited on a cost-effective stainless steel substrate by simple and inexpensive chemical bath deposition (CBD) method. The films are deliberated in provisos of their structural, morphological, optical and photoelectrochemical (PEC) properties before and after annealing treatment, using various physico-chemical techniques. The XRD studies showed the formation of triclinic phase of CTS films with nanocrystalline structure. Also, the crystallinity is enhanced with annealing and the secondary phase of Cu2S observed. Raman analysis confirmed the formation of CTS compound with secondary Cu2S phase. The SEM images also discovered mostly tiny spherical grains and significant progress in the size of grains after annealing. The films possess direct transitions with band gap energies of 1.35eV and 1.31eV before and after annealing, respectively. The improved photoconversion efficiency of CTS thin film based PEC cell is explained with the help of theoretical modeling of energy band diagram and correspondent circuit model of the impedance spectra.

Fabrication of Cu2SnS3 thin films by ethanol-ammonium solution process by doctor-blade technique

In the present study, a low-cost and simple method is applied to fabricate Cu2SnS3 (CTS) thin films. Namely CTS thin films are prepared by a doctor-blade method with a slurry dissolving the Cu2O and SnS powders obtained from CBD reaction solution into ethanol-ammonium solvents. Series of characterization methods including XRD, Raman spectra, SEM and UV-Vis analyses are introduced to investigate the phase structure, morphology and optical properties of CTS thin films. As a result, monoclinic CTS films have been obtained with the disappearance of binary phases CuS and SnS2 while increasing the annealing temperature and time, high quality monoclinic CTS thin films consisting of compact and large grains have been successfully prepared by this ethanol-ammonium method. Moreover, the secondary phase Cu2Sn3S7 is also observed during the annealing process. In addition, the post-annealed CTS film with a band-gap about 0.89 eV shows excellent absorbance between 400 and 1200 nm, which is proper for the bottom layer in multi-junction thin film solar cells.

Influence of Na in Cu2SnS3 film on its physical properties and photovoltaic performances

Cu2SnS3 (CTS) is the promising absorber of thin-film solar cell due to earth-abandant and non-toxic element. Influence of sodium (Na) on physical properties of CTS layers is investigated. In this work, CTS films with different Na concentrations are fabricated by sulfurizations of NaF/Cu/SnS2 and Cu/SnS2 stacked precursors on both soda-lime glass (SLG) and quartz substrates. The Na from NaF precursor layer and SLG substrate is introduced into CTS films. It is demonstrated that Na in forms of NaxCuSnS3 (x: 0.5–1.0) and Na2S is segregated in the large grain regions of CTS films. The crystal grains are significantly enlarged by Na addition into CTS films. As a result, the carrier lifetime, examined by time-resolved photoluminescence, is enhanced. From Raman scattering measurement, CTS films possess the peaks of monoclinic CTS structure. In addition, Cu2Sn3S7 and NaxCuSnS3 peaks are clearly observed in CTS films with high Na content. Finally, conversion efficiency of CTS thin-film solar cell is strongly enhanced from 0.61 (without Na addition) to 2.01% (with Na addition), mainly attributed to the increases in open-circuit voltage and fill factor through the decrease in carrier recombination.

Introduction of Na into Cu2SnS3 thin film for improvement of its photovoltaic performances

Impact of Na in Cu2SnS3 (CTS) films on their physical properties and photovoltaic performances is investigated. CTS films are fabricated by sulfurization of NaF/Cu/SnS2 stacked precursors. NaF precursor is used as primary Na source for Na introduction into the CTS films. It is demonstrated that Na content in the resulting CTS films is increased with enhancing thickness of NaF precursor, leading to the increase in Na/Cu atomic ratio but decrease in Cu/Sn atomic ratio. This suggests that the addition of NaF capping layer on the Cu/SnS2 stacked precursors suppresses evaporation of Sn-S compounds from the sample during sulfurization, thus forming Sn2S3 secondary. Therefore, with too thick NaF layer (greater than or equal to 75nm), Sn2S3 secondary phase in bulk and near surface of the resulting CTS films, having the detrimental effect on cell performances, is severely formed. However, the CTS grain sizes are notably enlarged as the thickness of NaF precursor increases. As a result, conversion efficiency of CTS thin-film solar cell with anti-reflective layer is increased up to 4.8% with the optimized NaF thickness of 60nm since the single-phase and large-grain CTS absorbing layer without Sn2S3 secondary phase near the surface is attained, thereby increasing open-circuit voltage and fill factor attributed to the decrease in the carrier recombination.

Na role during sulfurization of NaF/Cu/SnS2 stacked precursor for formation of Cu2SnS3 thin film as absorber of solar cell

Cu2SnS3 (CTS) is one of the intriguing absorbers owing to the earth-abandant and nontoxic element. Reaction paths for formations of CTS films through sulfurization of NaF/Cu/SnS2 (with NaF) and Cu/SnS2 (without NaF) stacked precursors are examined. It is revealed that Cu2SnS3 in the resulting film with NaF starts to be formed at the substrate temperature from 400°C, while Cu2SnS3 in the film without NaF begins to be formed at the substrate temperature over 500°C. The crystalline grains of resulting CTS films are markedly enlarged by Na addition, where Na is accumulated in the large grain area. The Na has a significant impact on the formation of CTS crystalline grains at lower substrate temperature, thus inducing the enlargement of the crystalline grains. In addition, the monoclinic CTS structure in the absorbers of the CTS solar cells can be formed at the lower temperature with the help of NaF. In addition, Cu2Sn3S7 phase and/or NaxCuSnS3 (x=0.5–1.0) are only observed in CTS films with NaF.

Fabrication of Cu2SnS3 thin-film solar cells with oxide precursor by pulsed laser deposition

In this paper, Cu2SnS3 (CTS) thin film is fabricated through sulfurization of oxide precursor which is deposited by pulsed laser deposition with a mixed CuO/SnO2 target. XRD and Raman analyses indicate a pure monoclinic Cu2SnS3 phase has been obtained by sulfurization at temperature from 500 to 600 °C. A compact and smooth film with polycrystalline structure is observed through SEM result. In addition, the CTS films show excellent absorbance with the band gap around 0.91 eV estimated by UV–Vis, which is suitable for the absorption layer of solar cells. Final devices were fabricated with a SLG/Mo/CTS/CdS/i-ZnO/AZO/Al structure. Device performance is improved with the temperature increasing. The best efficiency of CTS-based solar cells is 0.69% with an open-circuit voltage of 144 mV and a short-circuit current density of 18.30 mA/cm−2.

Physical Properties of Cu2SnS3 Thin Films Prepared by Sulfurization of co-sputtered Cu-Sn Metallic Precursors

In present study, Cu2SnS3 (CTS) thin films were prepared by sulfurization of co-sputtered Cu-Sn metallic precursors by varying the sulfurization temperature (Ts) in the range, 200-400°C and remaining deposition parameters were kept constant. The structural, microstructural, compositional and optical properties of the films were investigated. X-ray diffraction analysis indicated the (112) plane as preferred orientation with tetragonal crystal structure. Raman analysis showed the peaks allowed at 294 cm-1, 327 cm-1 and 348 cm-1 were characteristic modes of tetragonal CTS films. The AFM images revealed that the grains were uniformly distributed over the substrate surface and the average grain size, surface roughness, and skewness of the films were also estimated. EDS profiles confirm the presence of Cu, Sn and S elements in all the films and showed stoichiometric proportion of constituent elements present in the layer synthesized only at Ts=400°C. The optical band gap (Eg) of the as-grown films was estimated from the differential reflectance (dR/dE) versus photon energy spectra and decreased with increase of Ts from 1.66 eV to 1.45 eV. A detailed analysis of these results was presented and discussed.