Properties Of Cu2ZnSnS4 Thin Films Research Articles

Effects of pH Value in the Electrolyte on the Properties of Cu2ZnSnS4 Thin Film Fabricated by Single Step Co-Electrodeposition

CZTS thin films have been prepared from the electrolyte with different pH values by co-electrodeposition. The effects of bath pH value on the cyclic voltammetry, structure, morphology, composition and optical properties of CZTS thin films have been investigated in details. Cyclic voltammetry measurements reveal that pH value impacts the reduction potential of metals and the composition in precursors. The analyses of XRD and Raman spectroscopy suggest that the CZTS films have better crystallinity and less secondary phases when the bath pH is about 5.0. The chemical composition and morphological studies indicate the formation of compact and homogenous CZTS thin films with stoichiometric composition at a pH value of 5.0. And its bandgap energy is around 1.49 eV.

Effect of H2S Concentration and Sulfurization Temperature on the Properties of Cu2ZnSnS4 Thin Films

This study reports the effects of gas concentration on the properties of thin films. Specifically, sulfurization process with low concentrations of 0.05% and 0.1%, along with 5% gas, was studied. CZTS films were directly synthesized on Mo/Si substrates by chemical bath deposition method using copper sulfate, zinc sulfate heptahydrate, tin chloride dihydrate, and sodium thiosulfate pentahydrate. Smooth CZTS films were grown on substrates at optimized chemical bath deposition condition. The CZTS films sulfurized at low concentrations of 0.05 % and 0.1% showed very rough and porous film morphology, whereas the film sulfurized at 5% yielded a very smooth and dense film morphology. The CZTS films were fully crystallized in kesterite crystal form when they were sulfurized at for 1 h. The kesterite CZTS film showed a reasonably good room-temperature photoluminescence spectrum that peaked in a range of 1.4 eV to 1.5 eV, consistent with the optimal bandgap for CZTS solar cell applications.

Effect of annealing on structural and optical properties of Cu2ZnSnS4 thin films grown by pulsed laser deposition

In this work, we compare the effect of different types of thermal annealing on the morphological, structural and optical properties of Cu2ZnSnS4 (CZTS) thin films grown by reactive Pulsed Laser Deposition in H2S flow. Rutherford backscattering spectrometry, atomic force microscopy, X-ray diffraction, Raman spectroscopy and optical spectrophotometry data reveal dramatic increase of the band gap and the crystallite size without the formation of secondary phases upon annealing in N2 at the optimized conditions.

Control of composition and properties by the use of reflector wall in RF sputter deposition of Cu2ZnSnS4 thin films

The feasibility of composition and property controls by the use of the reflector wall, which is intended to enhance the probability that Zn and S atoms re-evaporated from the growing thin film surface re-impinge on the film surface, has been investigated in one-step RF-sputter deposition of Cu2ZnSnS4 thin films using a quaternary compound ceramic target. It is shown that the use of the reflector wall suppresses the composition deviation of deposited thin films from the stoichiometry and improves the crystallinity evaluated by X-ray diffraction, showing a larger crystalline diameter, especially in thin films deposited at a high substrate temperature of 400°C and by using the reflector wall with a temperature of 400°C. Film structures observed by cross sectional scanning electron microscopy also show the effectiveness of the use of the reflector wall. By the use of the heated reflector wall, as a result of the improvement in composition deviation and crystallinity, optical band gap decreases for all substrate temperatures. It is concluded that the use of the reflector wall suppresses the composition deviation from the stoichiometry in the quaternary compound thin films, resulting in the improvement of optical and electrical properties. The optimization of the conditions of the reflector wall and of substrate temperature will further enhance properties of Cu2ZnSnS4 thin films required as a solar-cell absorber layer.

Influence of precursor thin films stacking order on the properties of Cu2ZnSnS4 thin films fabricated by electrochemical deposition method

We fabricated Cu2ZnSnS4 (CZTS) thin films by electrochemically depositing precursor stacks on Mo-coated glass in a variety of orders: Cu/Sn/Cu/Zn, Cu/Zn/Cu/Sn, Zn/Cu/Sn/Cu, and Sn/Cu/Zn/Cu. Using Raman spectroscopy and X-ray diffraction, we found that for all stacking orders the annealed film was composed of a single CZTS phase with good crystallinity and strong (112) orientation. For the Cu/Sn/Cu/Zn stack, field-emission scanning electron microscopy revealed a homogeneous, compact surface morphology and large columnar grains. This stack also had an optical absorption coefficient of >104cm−1 and an optical band gap of 1.51eV. We fabricated a solar cell with the structure SLG substrate/Mo/Cu2ZnSnS4/CdS/i-ZnO Al:ZnO/Al, which achieved a conversion efficiency of 2.3%.

Comparative study on the annealing types on the properties of Cu2ZnSnS4 thin films and their application to solar cells

Comparative studies on the properties of Cu2ZnSnS4 (CZTS) thin films and performance of CZTS thin film solar cells (TFSCs) prepared by different sulfurization types such as commerical furnace (CF) and rapid thermal annealing (RTA) systems have been investigated. The CZTS thin film prepared using CF showed the dense microstructure with many voids and secondary phases, while that prepared using RTA showed the dense microstructure without void and with some secondary phases. The RTA annealed CZTS TFSC have shown better performance than that prepared using CF. The best performance of CZTS TFSC using RTA was 1.9% efficiency (Voc: 505mV,Jsc: 7.5mA/cm2 and FF: 50.2%).

Influence of triangle wave pulse on the properties of Cu2ZnSnS4 thin films prepared by single step electrodeposition

Quaternary chalcogenide Cu2SnZnS4 (CZTS) thin films were synthesized onto Mo-coated glass substrates using electrochemical deposition with different triangle wave pulse times (τ). The effects of the triangle wave pulse time on the structural, morphological, chemical and optical properties of the CZTS thin films were investigated. X-ray diffraction showed that the as-grown CZTS thin films are single phase, with a kesterite structure, strong preferential orientation along the (112) plane and a crystal size ranging from 23 to 36nm. FESEM images show that homogeneous, smooth, uniform, and densely packed grains could be formed, although the grain size and surface roughness depended on the triangle wave pulse time. UV–vis spectroscopy showed that the CZTS film had an optical absorption coefficient over 104cm−1 in the visible region and optical band gaps of the various films ranged from 1.36 to 1.47eV, suggesting that CZTS films can be useful absorbent layers in thin film solar cells. Solar cells were fabricated with SLG/Mo/CZTS/CdS/ZnO/ITO structures, and the best conversion efficiency obtained was 1.66% with Voc=571mV, FF=40.4 and Jsc=7.22mA/cm2.

Improved structural and optical properties of Cu2ZnSnS4 thin films via optimized potential in single bath electrodeposition

Here we report on the preparation of high quality Cu2ZnSnS4 thin films using single bath electrodeposition process via an optimized deposition potential. X-ray diffraction and Raman analysis validated the formation of kesterite phase of CZTS without any secondary phases at an optimized deposition potential of -1.4V vs. Ag/AgCl. As a signature of highly pure crystalline films of CZTS kesterite phase, we observed a characteristic Raman peak at 338cm−1 that corresponds to the vibration of sulfur atoms. Elemental analysis using energy dispersion analysis of X-rays (EDX) reveals a near ideal composition ratio of 2:1:1:4 for these films, and indicates the formation of the ideal stoichiometric compound. Furthermore, X-ray photoelectron spectroscopy analysis of the grown films illustrates an appropriate chemical composition and valence states of the constituent elements without a trace of free sulfur. Using the chrono- amperometry data and the Scharifker and Hill model we found that the nucleation mechanism for CZTS thin film is instantaneous. Optical properties demonstrated the optimum band gap of 1.5eV for kesterite CZTS film prepared from a precursor electrodeposited at -1.4V vs. Ag/AgCl. Mott-Schottky electrical measurements confirm the p-type nature of the film with a carrier concentration of 1017cm−3, a flat band potential of VFB=0.7V and space charge region width of 0.2μm.

Effect of rapid thermal processing conditions on the properties of Cu2ZnSnS4 thin films and solar cell performance

In the present work, we have studied the effect of several sulphurization conditions on the properties of Cu2ZnSnS4 thin films obtained through rapid thermal processing (RTP) of multi-period precursors with 8 periods of Zn/SnS2/CuS. In this study we varied the heating rate, the maximum sulphurization temperature, the time at maximum temperature and the amount of evaporated sulphur. The samples were characterized through scanning electron microscopy, energy dispersive spectroscopy, Raman scattering spectroscopy, X-ray diffraction, photoluminescence and I–V measurements. We have observed that at heating rates above 0.5°C/s the samples delaminated severely. As a result further tests were carried out at 0.2°C/s heating rate. The morphological studies revealed that the samples sulphurized at higher temperatures, shorter times and higher amount of evaporated sulphur exhibited larger grain sizes. The structural analysis based on Raman scattering and XRD did not lead to a clear distinction between the samples. Photoluminescence spectroscopy studies showed an asymmetric broad band characteristic of CZTS, which occurs in the range of 1.0–1.4eV and a second band, on the high energy side of the previous one, peaking at around 1.41eV. The intensity of this latter band varies from sample to sample revealing substantial differences in their optical properties. This band appears to originate either from the surface of the absorber or from the CdS layer and has a clear correlation with cell efficiency. The higher the intensity of this band the lower the cell efficiency, presumably due to the increase in recombination resulting from CZTS surface decomposition and eventually from the CdS with modified optoelectronic properties. The cell results hint toward a detrimental effect of long sulphurization times and a positive effect of higher sulphur vapour pressure and higher sulphurization temperature. Solar cell efficiencies improved with increased grain size in the absorber layer. The highest cell efficiency obtained in this study was 3.1%.

Mechanistic aspects of preheating effects of electrodeposited metallic precursors on structural and photovoltaic properties of Cu2ZnSnS4 thin films

Effects of 350°C preheating of electrochemically stacked Cu–Sn–Zn layers in an inert atmosphere on structural and morphological properties of quaternary kesterite Cu2ZnSnS4 (CZTS) films obtained by sulfurization of the metallic layers were investigated. When the CZTS film was fabricated without the 350°C preheating, the film contained a secondary Cu2SnS3 phase and other impurities. The CZTS film also showed poor adhesion to the bottom molybdenum (Mo) substrate with many crevices and voids in the film; a very thick MoS2 layer was formed at the top part of the Mo layer. These structural failures of the CZTS film were significantly reduced when the metallic precursor was preheated at 350°C before sulfurization for 20min: the CZTS film thus-obtained exhibited no secondary phases, good adhesion to the bottom Mo layer, flat and densely packed surface morphology, no appreciable crevices or voids, and formation of a relatively thin MoS2 layer. Based on results of studies on structural transformations during 350°C preheating and successive sulfurization, such differences in properties of resulting CZTS films are attributed to differences in formation pathways. Moreover, since 350°C preheating for a longer duration was found to be detrimental for the properties of resulting CZTS films, there should be an optimum duration of preheating to achieve a good CZTS film for solar cell application. As expected from these properties, the solar cell with an Al:ZnO/CdS/CZTS/Mo structure derived from the metallic precursor preheated at 350°C for 20min showed the best conversion efficiency of 5.6%.

Band positions and photoelectrochemical properties of Cu2ZnSnS4 thin films by the ultrasonic spray pyrolysis method

Cu2ZnSnS4 (CZTS) films were prepared by ultrasonic spray pyrolysis on FTO (SnO2 : F on glass) substrates. The effect of substrate temperatures on the phases, morphologies and photoelectrochemical properties of CZTS films was investigated. X-ray diffraction, Raman spectrum and energy-dispersive spectrometry were used to confirm the phases of the CZTS films. The samples at 400 and 450 °C exhibited a higher photocurrent than the samples at 350 and 500 °C. Moreover, the band positions of CZTS were measured by a facile Mott–Schottky method for the first time. Different from the previous calculation and experimental data, the conduction band position of CZTS was 0.26 eV higher than that of CdS. The results can explain well the low open circuit voltage of a CZTS-based solar cell and offer guidance to improving CZTS solar cells.

Physical properties of Cu2ZnSnS4 thin films deposited by spray pyrolysis technique

Thin films of Cu2ZnSnS4 (CZTS) were deposited on Pyrex substrates at various temperatures by spray pyrolysis technique from aqueous solution containing an economic stannous chloride (SnCl2) precursor for the tin and the effect of substrate temperature on the structural and opto-electronic properties was investigated. X-ray diffraction patterns and Raman spectroscopy reveal that all the CZTS films exhibited kesterite structure with preferential orientation along the (1 1 2) direction and some secondary phases. Also, they possessed different band gaps, which were found to lie between 1.52 and 1.81 eV, indicating that CZTS compound has absorbing properties favorable for applications in solar cell devices. Van der Pauw technique and Hall effect measurements were used to determine the electrical properties of CZTS films and the resistivity was of about 0.12 Ω cm for film grown at 280 °C.

Research on the photoresponse current and photosensitive properties of Cu2ZnSnS4 thin film prepared by sulfurization of a sputtered metal precursor

The photoresponse current and photosensitive properties under different electrical field were studied for Cu2ZnSnS4 films. A persistent photoconductivity effect of Cu2ZnSnS4 film was observed and the effect of the electrical field on the decay time of photo excited current was investigated. The decay time of photo excited current of CZTS decreased from 378 s to 0.341 s with the electrical field reducing from 1 V to 1 × 10−4 V, respectively. Under lower electrical fields, the “instantaneous” jump and drop of current appeared respectively when the light was turned on and off. The durations of the “instantaneous” jump process decreased from 0.1826 s to 0.0736 s with the electrical field reducing from 1 V to 1 × 10−4 V, and durations of the “instantaneous” drop process decreased from 0.1588 s to 0.0698 s with the electrical field reducing from 1 V to 1 × 10−4 V, respectively. It was found that the change trends in the duration of “instantaneous” jump and drop stage with the electrical field are accord with the exponential decay function. From the exponential decay function, the durations of the “instantaneous” jump (Y1(0) = 0.0658 s) and drop (Y2(0) = 0.0681 s) were obtained in the case without an electrical field.

Dependence of Copper Concentration on the Properties of Cu2ZnSnS4 Thin Films Prepared by Electrochemical Method

Dependence of Copper Concentration on the Properties of Cu2ZnSnS4 Thin Films Prepared by Electrochemical Method

Effect of the Deposition Time onto Structural Properties of Cu2ZnSnS4 Thin Films Deposited by Pulsed Laser Deposition

The <TEX>$Cu_2ZnSnS_4$</TEX> (CZTS) thin film solar cell is a candidate next generation thin film solar cell. For the application of an absorption layer in solar cells, CZTS thin films were deposited by pulsed laser deposition (PLD) at substrate temperature of <TEX>$300^{\circ}C$</TEX> without post annealing process. Deposition time was carefully adjusted as the main experimental variable. Regardless of deposition time, single phase CZTS thin films are obtained with no existence of secondary phases. Irregularly-shaped grains are densely formed on the surface of CZTS thin films. With increasing deposition time, the grain size increases and the thickness of the CZTS thin films increases from 0.16 to <TEX>$1{\mu}m$</TEX>. The variation of the surface morphology and thickness of the CZTS thin films depends on the deposition time. The stoichiometry of all CZTS thin films shows a Cu-rich and S-poor state. Sn content gradually increases as deposition time increases. Secondary ion mass spectrometry was carried out to evaluate the elemental depth distribution in CZTS thin films. The optimal deposition time to grow CZTS thin films is 150 min. In this study, we show the effect of deposition time on the structural properties of CZTS thin film deposited on soda lime glass (SLG) substrate using PLD. We present a comprehensive evaluation of CZTS thin films.

Effect of post-sulfurization on the composition, structure and optical properties of Cu2ZnSnS4 thin films deposited by sputtering from a single quaternary target

Quaternary Cu2ZnSnS4 (CZTS) thin films were deposited on heated glass substrates directly from a non-stoichiometric quaternary CZTS target by radio-frequency (RF) magnetron sputtering process, followed by post-sulfurization in atmosphere of Ar+H2S(5%). The results of X-ray diffraction (XRD), Raman spectra, and scanning electron microscope (SEM) show that post-annealed process can improve the crystallinity of CZTS thin films. Both XRD and Raman spectra analysis indicate the internal compressive stress relaxes in post-annealed CZTS thin films. Further transmission spectra demonstrate that the band gaps of post-annealed CZTS thin films are smaller than those of as-deposited due to the relaxation of internal compressive stress and the increase of Cu content in the post-annealed CZTS films.

Comparative study of the influence of two distinct sulfurization ramping rates on the properties of Cu2ZnSnS4 thin films

The Cu2ZnSnS4 (CZTS) are produced by sulfurization of precursors cosputtering from Cu2Sn and ZnS targets at two distinct ramping rates (2°C/min and 21°C/min). Through the comparative analyses of scanning electron microscopy (SEM), energy dispersive of X-ray (EDS), X-ray diffraction (XRD), transmittance and Raman spectrum, it has been revealed that heating rate has a great impact on the reaction mechanism and characters of CZTS. The rapid heating rate 21°C/min has resulted in the appearance of bubble-like morphology and the concurrency of amorphous phases with CZTS. CZTS absorbers sulfurized at 2°C/min have exhibited a better crystallographic quality revealed by Raman spectroscopy and XRD pattern. However, XRD and transmittance have proved n-type SnS and Cu4Sn7S16 phases concurrent with the slowly ramped CZTS films. Difference in the two ramping rates has also resulted in the variance of band gap and Raman primary mode of the final films. The slow sulfurization (2°C/min) superior to the rapid one (21°C/min) is beneficial to the growth of the expected CZTS in this work.

H2S Concentration Dependence of Properties of Cu2ZnSnS4 Thin Film Prepared under Nonvacuum Condition

Cu2ZnSnS4 (CZTS) thin films were prepared by a sol–gel sulfurization method. Sulfurization was carried out in H2S of various concentrations and the properties of the films were investigated. The CZTS thin films sulfurized at 500 °C for 1 h in 0.5 and 3% H2S atmospheres had large grains compared with the film sulfurized in 1% H2S atmosphere. From the X-ray diffraction analysis, the CZTS thin film sulfurized for 1 h in 0.5% H2S atmosphere included a small amount of CuxS as a secondary phase. The films sulfurized for 1 h in 1 and 3% H2S atmospheres were composed of a CZTS phase without CuxS. Owing to the long sulfurization process, the CuxS phase was eliminated and the optical properties of the films were improved. The size of the grains sulfurized in 1% H2S increased with increasing sulfurization time from 2 to 3 h.

Dependence on Annealing Temperature of Properties of Cu2ZnSnS4 Thin Films Prepared by Sol–Gel Sulfurization Method

Cu2ZnSnS4 (CZTS) thin films were fabricated using a rapid thermal process in 5% H2S+ N2 atmosphere from precursors prepared by the sol–gel method. The precursors were preheated at 250 °C for 10 min and then sulfurized at different temperatures from 300 to 600 °C for 10 min. XRD studies showed that the samples sulfurized at 500–600 °C had a CZTS structure. With increasing sulfurization temperature, the chemical composition ratio of sulfur/metal and the grains size of CZTS increased. From the (αh ν)2–hν plot, the CZTS films had a band gap of ∼1.5 eV.

Dependence on Annealing Temperature of Properties of Cu2ZnSnS4Thin Films Prepared by Sol–Gel Sulfurization Method

Dependence on Annealing Temperature of Properties of Cu₂ZnSnS₄Thin Films Prepared by Sol–Gel Sulfurization Method