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The electrical and optical properties of electron or proton-irradiated Cu2ZnSnS4 (CZTS) solar cells were investigated. The normalized efficiency of CZTS solar cells decreased when fluence was greater than ~ 1015 cm− 2 for electron irradiation or 1012 cm− 2 for proton irradiation. This tendency is quantitatively the same as that of Cu(In,Ga)Se2 (CIGS) solar cells, and better than that of Si solar cells. One of the origins of degradation is the formation of deep defects such as Cu atoms substituted at Zn sites and nonradiative recombination centers in the CZTS layer, as suggested by the decreasing photoluminescence peak intensity at 1.2 eV with increasing irradiation fluence. On the other hand, the solar cell performance improved in the case of a small amount of electron or proton irradiation due to the bombardment soaking effect. These results indicate that the CZTS solar cells show excellent tolerance of electron and proton radiation, similar to a CIGS solar cell.

In this study, Cu 2 ZnSnS 4 (CZTS) formation by co-evaporation and subsequent annealing in S-flux was demonstrated using molecular beam epitaxy(MBE) system and the influence of the S-flux annealing temperature on the CZTS formation was investigated. At the films formed by co-evaporation of Cu, Zn, Sn and S at 320 °C and subsequent annealing in S-flux at 320–450 °C, CZTS and Cu 2 − x S phases were detected and those formations were found to have strong dependence on the S-flux annealing temperature. For annealing temperature, detected CZTS has maximum amount at the range of 380–420 °C. On the other hand, detected Cu 2 − x S is minimum amount at that temperature range. Depth profile of those films showed that significant Cu segregation occurred to the film surface above 400 °C of S-flux annealing temperature. These results suggest that the CZTS phase with less secondary phase of Cu 2 − x S, which has worse impact on the solar cell performance, is formed in the limited temperature range of 380–420 °C of S-flux annealing performed after co-evaporation. 2.25% power conversion efficiency was achieved at the solar cell with CZTS formed by the co-evaporation at 320 °C and subsequent S-flux annealing at 400 °C.

Half-tracked tractors equipped with front wheels and a rear oscillating crawler unit are popular. However, the track tension fluctuates caused by the variation in the unit's perimeter because the hitch point of the oscillating frame is set separately from the drive axis of the drive sprocket. It is considered that this fluctuation in the track tension could influence driving performance. Moreover, driving performance factors might be optimized by actively controlling the track tension. Therefore, this paper aims to propose a measurement method for track tension fluctuation, which focuses on the inner structure of the rubber track. The rubber track contains a structure of capacitors constructed with a steel cord as a capacitor plate and the rubber between the steel cords as the electric material. When the tension force acts upon the rubber track, changing the distance between the steel cords, the capacitance would be changed. This capacitance variation was measured in the oscillating frequency by a CR oscillating circuit that utilized the characteristic of a capacitor. A fundamental experiment with a test piece cut out of a rubber track was carried out to evaluate the effectiveness of the proposed tension measurement, which uses steel cords arranged inner the rubber track. As a results, it was theoretically confirmed that the oscillating frequency was reduced by increasing the tension load, and a stable value with a high correlation between the tension load and the oscillating frequency. In conclusion, this study has demonstrated the possibility for stable measurement of crawler tension.

We have investigated the influence of sodium (Na) on the properties of co-evaporated Cu2ZnSnS4 (CZTS) layer microstructures and solar cells. The photovoltaic performance and diode properties were improved by incorporating Na from NaF layers into the CZTS layers, while Na had a negligible effect on the microstructural properties of the layer. The best cell fabricated by using an optimal CZTS layer (Cu/(Zn + Sn) = 0.70, Zn/Sn = 1.8) yielded an active area efficiency of 5.23%. The analysis of device properties suggests that charge-carrier recombination at CZTS/CdS interface is suppressed by intentional Na incorporation from NaF layers. Copyright © 2016 John Wiley & Sons, Ltd.

In this work, we investigated the effect of surface treatment of the Cu2ZnSnS4 (CZTS) thin films using ammonia solution. CZTS thin films were prepared by RF sputtering using single CZTS target with sulfurization process. In order to study the effect of surface treatment using ammonia solution, solution temperature was varied. Structural properties of the samples are almost same with and without ammonia surface treatment measured by XRD and Raman spectroscopy. From the measurement of the chemical composition, the Zn is dissolved by ammonia solution. In addition, the removal rate of oxygen and sodium is different between deionised water and ammonia solution. Ammonia could have prevented their removal from the surface to solution. (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Oleylamine-capped tin disulfide nanoparticles were prepared by the hot-injection method using tin (II) chloride (SnCl2.5H2O) and thioacetamide as tin (II) and sulfur precursors, respectively. The as-prepared nanoparticles were rinsed with ethanol or toluene, and their structural and morphological were assessed by X-ray diffraction, Raman spectroscopy, scanning electron microscopy and transmission electron microscopy. The obtained nanoparticles were single-phase SnS2 with hexagonal structure. These nanoparticles self-assembled to produce spherical 40-50 nm nanostructures after ethanol evaporation, whilst rhombohedral-shaped nanostructures or round-edge nanoribbons were produced after the toluene evaporation. (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Cu2ZnSnS4 (CZTS) material has many advantages for high-efficiency thin-film solar cell absorber layer. A detailed study of the surface of the CZTS and the hetero-interface of the CZTS/buffer layer is important to improve the conversion efficiency of CZTS thin film solar cells. We investigated the surface condition of the CZTS films by carrying out the surface treatment using bromine solution. The activation energy of the etching using bromine solution was estimated from the slope of the line fitting the graph of the temperature dependence of the etching rate. The activation energy is about 0.35 eV. This value suggests that etching mechanism of CZTS using bromine solution is diffusion-limited process. There were no significant changes in the structural characteristics after surface treatment by X-ray diffraction and Raman spectroscopy. From the results of X-ray photoelectron spectroscopy measurements, a relative surface composition was shifted to Cu- and Zn-rich phase after surface treatment. (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The ternary compound Cu2SnS3 (CTS) is composed of elements that are low in cost, non-toxic, and abundant in the Earth's crust. In addition, CTS is a p-type semiconductor with a high reported absorption coefficient of more than 104 cm−1 and a band gap energy of 0.92–1.77 eV. It is, therefore, considered to be a suitable candidate for the absorber layer in thin film solar cells. In the present study, CTS thin films were produced by first depositing precursor films by co-evaporation of Cu, Sn, and S, and then annealing them. Solar cells were then fabricated using the CTS films as absorber layers, and the dependence of their photovoltaic properties on the annealing temperature was investigated. The solar cell using the CTS thin film annealed at 570 °C exhibited an open-circuit voltage of 248 mV, a short-circuit current density of 33.5 mA/cm2, a fill factor of 0.439, and a conversion efficiency of 3.66%.

Cu2ZnSnS4 (CZTS) is one of the promising materials for high efficiency thin film solar cells. Here we report on the chemical and structural characterization of the CZTS thin films before and after the surface treatment using deionized water. X-ray diffraction and Raman scattering spectroscopy results showed that the deionized water treatment did not affect the bulk characterization. Copper chemical composition ratio increases and sulphur composition ratio decreases with increasing deionized water treatment temperature on the film surface. In the case of the sample treated at 353 K, the surface composition changes to Cu-rich composition. However, the chemical composition ratio of the bulk still remained before deionized water (DIW) surface treatment. The change in the CZTS surface composition according to the DIW surface treatment temperature, we think these results may help to be studied in CZTS surface in more detail. (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Cu2(2.00-x)((2In)y (ZnSn)(1.00-y))x S4 crystals were grown from the melt. 23 samples with different x and y values were synthesized by heating constituent elementary Cu, In, S and Zn-Sn alloy at 1,250 °C for 10 hours in each evacuated fused-quartz ampule. All samples were characterized by powder X-ray diffraction analysis. Two peaks are seen at the 112 diffraction positions in 0.3 ≤ y ≤ 0.9. The FWHM of the 112 diffraction peak broadened in 0.2 ≤ y ≤ 0.7. Lattice constants were obtained by Rietveld method using two tetragonal structure models simultaneously in the refinement. Both a and c obtained as CuInS2 phase changed almost linearly in y ≥ 0.7; therefore the existence of CuInS2 phase solid solution containing Zn and Sn was indicated in this region. The miscibility gap was also suggested as the region of 0.2 ≤ y ≤ 0.7 in our results because of the shape and the broadening of the 112 diffraction peaks. (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The ternary compound semiconductor Cu2SnS3 (CTS) is formed from non-toxic materials that are abundant in Earth's crust and other low-cost elements. CTS has also been reported to a band gap energy range of 0.93–1.77 eV and an absorption coefficient of 1.0×104 cm–1. Consequently, CTS is a potential material for the p-type absorber layer of thin film solar cells. In this study, we examined the dependence of the optical, electrical and photovoltaic properties of CTS thin films on the Cu/Sn composition ratio. CTS thin films were fabricated by sulfurizing evaporated Cu-Sn precursors with different Cu/Sn composition ratios at 560 °C for 2 h in a N2 atmosphere and sulfur vapor. The Cu/Sn composition ratios of the sulfurized films were determined to be 1.6–2.5 by X-ray fluorescence. The solar cell comprising a CTS thin film with a Cu/Sn composition ratio of 1.77 exhibited the best performance among the cells examined, an open-circuit voltage of 242 mV, a short-circuit current density of 28.9 mA/cm2, a fill factor of 41.7% and a conversion efficiency of 2.92% were obtained. (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

In our laboratory, the development of Cu2ZnSnS4 (CZTS) solar cells has been conducted. It is said that the conversion efficiency of Cu(In,Ga)Se2 (CIGS) was improved by the diffusion of Sodium (Na) from Soda Lime Glass (SLG) substrate. In this study, the effect of Na-addition on CZTS solar cells was examined. Firstly, we deposited Mo bottom electrode on photovoltaic glass substrate by using an RF sputtering method. Then, CZTS precursor and Sodium Fluoride (NaF) were sequentially deposited on it. Then we sulfurized them in an atmosphere of Hydrogen Sulfide. So, the sodium was diffused from the both side of the CZTS surface and the substrate. From the C-V measurement, as the amount of thickness of NaF increased, the carrier density increased. At the same time, the open circuit voltages of CZTS solar cells were enhanced from 630mV to 655mV. From these findings, we confirmed that the improvement in PV characteristics was partly due to the increase of the carrier density by Na-addition effect on CZTS.

About 20 years ago, in 1995, we had started to develop the novel thin film solar cells using CZTS as an absorber to be able to use in the after next generation. The conversion efficiency of CZTS thin film solar cells reported for the first time in 1996 was only 0.66% and it had been improved to about 7% in our laboratory. Because the potential of CZTS-based thin film solar cells seems to be quite high, we will be able to overcome the resource problem of rare-metal in the near future. In this review manuscript we will survey our previous works and show the recent results concerning with this promising solar cells.

The crystal structure of Cu 2 ZnSnS 4 (CZTS) thin films fabricated by vapor-phase sulfurization was determined using X-ray anomalous dispersion. High statistic synchrotron radiation X-ray diffraction data were collected from very small amounts of powder. By analyzing the wavelength dependencies of the diffraction peak intensities, the crystal structure was clearly identified as kesterite. Rietveld analysis revealed that the atomic composition deviated from stoichiometric composition, and the compositions were Cu/(Zn + Sn) = 0.97, and Zn/Sn = 1.42.

Cu2SnS3 (CTS) p-type semiconductors are expected to be applied as a light absorption material for low-cost thin-film solar cells due to their advantageous physical properties. The influence of sodium addition to CTS thin films was investigated by comparing Na-free CTS and Na-doped CTS fabricated on alkali-free glass substrates. Grain growth for Na-free CTS, which has a Cu/Sn composition ratio of approximately 2.0, did not occur below 570 °C. In contrast, the addition of sodium to the CTS increased the grain sizes with an increase in the annealing temperature. Even with Na-free and Na-doped CTS, the grain sizes increased with a decrease in the Cu/Sn composition ratio. These results show that an excess of Sn combined with the presence of sodium accelerate the grain growth of CTS. Photovoltaic cells using the Na-doped CTS with a Cu/Sn ratio of 1.81 exhibited an open-circuit voltage of 242 mV, a short-circuit current density of 26.5 mA/cm2, a fill factor of 0.523, and a conversion efficiency of 3.35%. The cells using CTS without sodium did not exhibit good photovoltaic characteristics due to the small grain sizes.

Cu2ZnSnS4 (CZTS) thin films are highly suitable as the light-absorbing layer in solar cells. In this study, Cu, Zn, Sn, and S are co-evaporated on the Mo/soda-lime glass (SLG) surface at 320 °C and then annealed in sulfur flux at temperatures of 320–450 °C within the same molecular beam epitaxy system (one-stop process). The Raman spectroscopy of the coated surfaces shows that CZTS is formed with a secondary Cu2− x S phase, where the relative concentrations of the phases strongly depend on the annealing temperature. With an increase in the annealing temperature above around 400 °C, the fraction of CZTS decreases and that of Cu2− x S increases. The depth profile analysis shows that Cu segregates to the surface and Cu2− x S is formed on the film. The solar cells fabricated on these samples show that photovoltaic performance is limited by the surface Cu2− x S. The observed external quantum efficiency behavior is consistent with the degradation of carriers collected in the solar cell formed on the CZTS film owing to the presence of the secondary Cu2− x S phase.

Cu 2 ZnSnS 4 (CZTS) thin films were prepared by sulfurizing precursors deposited by electroplating. The precursors (Cu/Sn/Zn stacked layers) were deposited by electroplating sequentially onto Mo-coated glass substrates. Aqueous solutions containing copper sulfate for Cu plating, tin sulfate for Sn plating and zinc sulfate for Zn plating were used as the electrolytes. The precursors were sulfurized by annealing with sulfur at temperatures of 300, 400, 500 and 600 °C in an N 2 gas atmosphere. The X-ray diffraction peaks attributable to CZTS were detected in thin films sulfurized at temperatures above 400 °C. A photovoltaic cell using a CZTS thin film produced by sulfurizing an electroplated Sn-rich precursor at 600 °C exhibited an open-circuit voltage of 262 mV, a short-circuit current of 9.85 mA/cm 2 and an efficiency of 0.98%.

The low cost, environmental harmless Cu 2 ZnSnS 4 (CZTS)-based thin film solar cells are fabricated by using abundant materials. The CZTS film possesses promising characteristic optical properties; band-gap energy of about 1.5 eV and large absorption coefficient in the order of 10 4 cm − 1 . All constituents of this CZTS film, which are abundant in the crust of the earth, are non-toxic. Therefore, if we can use CZTS film practically as the absorber of solar cells, we will be free from both of the resource saving problem and the environmental pollution. In our CZTS project, CZTS absorber films were prepared by two independent techniques. One is three rf sources co-sputtering followed by annealing in sulfurized atmosphere. The latest conversion efficiency of over 6.7% was achieved by this technique. The other is co-evaporation technique. CZTS films were grown on Si (100) by vacuum co-evaporation using elemental Cu, Sn, S and binary ZnS as sources. XRD patterns indicated that the polycrystalline growth was suppressed and the orientational growth was relatively induced in a film grown at higher temperatures. In this presentation, the development of CZTS-based thin film solar cells will be surveyed.

From 2006, Nagaoka National College of Technology (NNCT) , Niigata Industrial Creation Organization (NICO) and Society of Embedded Software Skill Acquisition for Managers and Engineers (SESSAME) began a joint training program for embedded systems development engineers. The courses consist of a basic course, a practical course, an intermediate course and PBL course according to ability of student. The training curriculum of the courses is planed corresponding to ETSS in cooperation with IPA-SEC. In this paper, the content of the training program for embedded system development engineers is described and the results are discussed. In addition, the application of teaching materials which were developed in this project can now be used to benefit the students and instructors of NNCT.

Stacked precursors of Cu, Sn, and Zn were fabricated on glass/Mo substrates by electron beam evaporation. Six kinds of precursors with different stacking sequences were prepared by sequential evaporation of Cu, Sn, and Zn with substrate heating. The precursors were sulfurized at temperatures of 560 °C for 2 h in an atmosphere of N2 + sulfur vapor to fabricate Cu2ZnSnS4 (CZTS) thin films for solar cells. The sulfurized films exhibited X-ray diffraction peaks attributable to CZTS. Solar cells using CZTS thin films prepared from six kinds of precursors were fabricated. As a result, the solar cell using a CZTS thin film produced by sulfurization of the Mo/Zn/Cu/Sn precursor exhibited an open-circuit voltage of 478 mV, a short-circuit current of 9.78 mA/cm2, a fill factor of 0.38, and a conversion efficiency of 1.79%.

Cu 2 ZnSnS 4 films were grown on Si (100) by vacuum evaporation using elemental Cu, Sn, S and binary ZnS as sources. X-ray diffraction patterns of films grown at different substrate temperatures indicated that polycrystalline growth was suppressed and the orientational growths were relatively induced in a film grown at higher temperatures. Tetragonal structure of Cu 2 ZnSnS 4 films was confirmed by studying RHEED patterns. The existence of c -axis ([001] direction) growth, two kinds of a -axis (〈100〉 direction) growth and four kinds of {112} twins which can be classified as two symmetrical pairs is proposed. Broad emissions at around 1.45 eV and 1.31 eV were observed in the photoluminescence spectrum measured at 13 K.

We have investigated the deposition of Al-doped ZnO (AZO) films using a radio frequency (rf) magnetron sputtering apparatus with a mesh grid electrode. The improvement of the uniformity of crystallinity was achieved by the effect of the appropriate negative grid biases that suppress the impingement of charged particles onto the films surface. The uniformity of the electronic properties such as resistivity, carrier concentration and Hall mobility was also improved.

Cu(In,Ga)S 2 crystals have been grown from the melt using constituent elementary substances as sources. The chalcopyrite structure was confirmed by powder X-ray diffraction patterns. Lattice parameters a and c changed almost linearly corresponding to the composition ratio between In and Ga. The amplitudes of photo-acoustic signals changed greatly near the band gap energies. This phenomenon is due to the changes of the absorption coefficient. Band gap energies, estimated from the photo-acoustic spectra, also showed continuous change with the composition.

Aiming to develop the solar cells free from the environmental contaminants, promising solar cell of a thin film type could be produced by using Cu 2 ZnSnS 4 (CZTS) film as the absorber. The CZTS film possesses promising characteristic optical properties; band gap energy of about 1.5 eV and large absorption coefficient in the order of 10 4 cm −1 , which means large possibility of commercial production of the most suitable absorber by using the CZTS film. In addition, as the CZTS film contains neither rare metals nor toxic materials, combining this film with Cd-free buffer layer, we can expect coming solar cells with nontoxic thin films in the near future. CZTS thin films were able to be produced successfully in our previous work by vapor phase sulfurization of the stacked precursors that were prepared by sequential vacuum evaporation of Cu, Sn, and ZnS. The best conversion efficiency with the heterojunction of ZnO:Al/CdS and CZTS was 5.45%, which showed the possibility of a very low cost solar cell. It has been, however, quite difficult to prepare CZTS film with high reproducibility. This paper showed the photovoltaic properties of CZTS-based thin film solar cells fabricated by using three types of precursors: (1) the conventional precursor with stacked layers of Cu/Sn/ZnS, (2) the modified precursor with the stacking order of Sn/Cu/ZnS, and (3) the precursor with five periods of Cu/SnS 2 /ZnS, which was produced to increase the amount of S and to enhance the interdiffusion in precursor.

Cu(In,Ga)S 2 films were grown on Si(100) by vacuum evaporation using the constituent elementary substances as sources. It was found from X-ray diffraction studies that orientational growth occurred in a limited temperature region. The chalcopyrite structure was confirmed by studying RHEED patterns. The existence of c -axis growth, two kinds of a -axis growth and four kinds of {112} twins which can be classified as two symmetrical pairs is proposed.

Cu2ZnSnS4 (CZTS) is considered as a non-toxic and low-cost absorber material for solar cells, which has optimum direct bandgap energy for solar energy absorption and high absorption coefficient. In order to achieve higher solar cell efficiencies of CZTS, a better understanding about its defect structure is required. In this study, the defect levels of CZTS are investigated by means of photoluminescence measurements. At temperatures lower than 150 K, a broad emission band around 1.17 eV was observed. The emission band around 1.38 eV was observed at temperatures higher than 125 K. Measurements of PLE spectra for these two emissions have been performed. The emission at 1.17 eV is found to be from the CZTS layer, and its thermal activation energy of 40 ± 9 meV was obtained from the temperature dependence of PL spectra. The emission at 1.38 eV is found to be from the CdS layer.

CuInS2-Cu2ZnSnS4 crystals were synthesized by the pressure-less sintering method using CuInS2 and Cu2ZnSnS4 powders grown from each melt. The x values in Cu2(2In)x(ZnSn)(1.00−x)S4 were evaluated by energy dispersive spectroscopy. Lattice constants were derived from powder X-ray diffraction analysis by Rietveld method. Lattice constants of CuInS2 phase changed linearly at x ≥ 0.49. On the other hand, lattice constants of Cu2ZnSnS4 phase changed almost linearly at x ≤ 0.37. In Raman spectra, peak positions of A (I4¯) or A1 (I4¯2m) mode of Cu2ZnSnS4 phase changed toward the lower wavenumber side linearly with increasing x. A1 mode of CuInS2 phase became weaker with decreasing x, and disappeared below x = 0.49. In PL spectra measured at 15 K, broad peaks at about 1.26 eV were observed at 0.00 ≤ x ≤ 0.85.

Cu2ZnSnS4 (CZTS) is one of the promising materials of absorber layer used in thin film solar cells. In this paper, we revealed the effects of surface treatment by hydrogen peroxide solution on the chemical and structural properties of CZTS thin films in order to improve the conversion efficiency. On the Raman spectra, the full width at half maximum (FWHM) of A1 peak at around 338 cm−1 is not affected by H2O2 solution treatment. However, Raman scattering spectroscopy results showed that the existence of not only CZTS but also oxide was confirmed by the H2O2 solution treatment. From the XPS spectra, Zn, and S were dissolved by H2O2 solution. The surface oxidation takes place in a very short period of time. The sulfate phase is existence on the CZTS surface by H2O2 surface treatment.

Cu2ZnSnS4 bulk polycrystalline were synthesized by pressureless sintering (PLS) method in vacuum and spark plasma sintering (SPS) method. It was confirmed that there were no the secondary phases in a sample sintered by SPS method at 750 °C from the results of powder X-ray diffraction (XRD) patterns and Rietveld refinement. The Raman spectrum of the sample showed the strongest peak at 338 cm−1 with a shoulder at 350–370 cm−1, and the weaker peaks at about 255 and 289 cm−1, which originated from Cu2ZnSnS4. The FWHM of the strongest peak of 7.4 cm−1 was narrower than other samples. The photoluminescence (PL) spectrum measured at 15 K were observed a broad emission band with the maximum at 1.26 eV. Also, the measured photoluminescence excitation (PLE) for the band-edge emission was originated the energy transfer from the band-to-band excitation.The obtained activation energy was 62 ± 9 meV.

Cu 2 ZnSnS 4 (hereafter CZTS) thin films were successfully formed by vapor-phase sulfurization of precursors on a soda lime glass substrate (hereafter SLG) and a Mo-coated one (hereafter Mo-SLG). From the optical properties, we estimate the band-gap energy of this thin film as 1.45–1.6 eV which is quite close to the optimum value for a solar cell. By using this thin film as an absorber layer, we could fabricate a new type of thin film solar cell, which was composed of Al/ZnO:Al/CdS/CZTS/Mo-SLG. The best conversion efficiency achieved in our study was 2.62% and the highest open-circuit voltage was 735 mV. These device results are the best reported so far for CZTS.

Cu2ZnSnS4 (CZTS) thin films were prepared by sulfurization of electrodeposited Cu-Zn-Sn precursors. The Cu-Zn-Sn precursors were deposited on Mo-coated glass substrates in a one-step process from an electrolyte containing copper (II) sulfate pentahydrate, zinc sulfate heptahydrate, tin (II) chloride dehydrate and tri-sodium citrate dehydrate. The precursors were sulfurized by annealing with sulfur at temperatures of 580 °C and 600 °C in an N2 atmosphere. X-ray diffraction peaks attributable to CZTS were detected in the sulfurized films. Photovoltaic cells with the structure glass/Mo/CZTS/ CdS/ZnO:Al/Al were fabricated using the CZTS films by sulfurizing the electrodeposited precursors. The best photovoltaic cell performance was obtained with Zn-rich samples. An open-circuit voltage of 540 mV, a short-circuit current of 12.6 mA/cm2 and an efficiency of 3.16% were achieved. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The development of environment friendly type thin film solar cell Cu2ZnSnS4 (say CZTS-type) fabricated using abundant materials is introduced in this paper. Three RF sources co-sputtering continued with vapor phase sulfurization method (inline-type vacuum apparatus) is utilized. Those processes were sequentially done in different apparatus in our previous work. In this study, an inline-type vacuum apparatus is firstly introduced to acquire higher quality of CZTS films. Inductively Coupled Plasma Spectroscopy (ICPS) is used to analyze the minute material composition of CZTS thin film solar cell. By optimizing the material composition, 5.74% of conversion efficiency is obtained. It is the best data for CZTS-type thin film solar cells at present.

Cu2ZnSnS4 (henceforth CZTS) absorber layers are successfully synthesized by a sulfurization technique of physical vapor deposited precursors. In our previous report, we have clarified that the off-stoichiometry composition of Cu-poor and Zn-rich is desirable to achieve high conversion efficiency. By using CZTS compound target that provide such active composition, we could conduct a simple single sputtering method to prepare CZTS absorber. In our laboratory, a two-stage process of precursor preparation followed by sulfurization is a major fabrication method from the start of this study. We think that this method is suitable for a mass production. An optimization of the sulfurization process is a quite important issue because the active composition was already revealed. In this paper, TG/DTA system available in the H2S atmosphere is introduced to optimize the sulfurization condition. As a result, bump-free CZTS films were prepared successfully and the fluctuation of J-V properties in one substrate was drastically suppressed.

By sulfurization of EB evaporated precursors, CZTS(Cu2ZnSnS4) films could be prepared successfully. This semiconductor does not consist of any rare-metal such as In. The X-ray diffraction pattern of CZTS thin films showed that these films had a stannite structure. This study estimated the optical band gap energy as 1.45 eV. The optical absorption coefficient was in the order of 104cm−1. The resistivity was in the the order of 104 Ω cm and the conduction type was p-type. Fabricated solar cells, Al/ZnO/CdS/CZTS/Mo/Soda Lime Glass, showed an open-circuit voltage up to 400 mV.

In 1988, K. Ito and T. Nakazawa of Shinshu University succeeded in fabrication of Cu 2 ZnSnS 4 (CZTS) thin films by an atom beam sputtering method and confirmed that CZTS has suitable optical properties for thin film solar cells. In 1995, we began to develop the novel thin film solar cells using CZTS as an absorber to be able to use in the after next generation. The conversion efficiency of CZTS thin film solar cells reported for the first time in 1996 was only 0.66% and it have been improved to 6.77% in these twelve years at our laboratory. Quite recently, IBM using CZTSSe that contain Se to some extent achieved the conversion efficiency of over 10%. Because the potential of CZTS-based thin film solar cells seems to be quite high, we will be able to overcome the resource problem of rare-metal in the near future. In this talk we will survey our previous works and show the recent results concerning with this promising solar cells.

The crystal structure of Cu2ZnSnS4 thin films obtained by vapor phase sulfurization is determined by synchrotron XRD measurements using the anomalous dispersion effect.