Mo-coated Soda-lime Glass Research Articles

Photoelectrochemical and Photovoltaic Performance of As-deposited Ink-based CuInS2 Heterojunction Thin Film

In this report, we demonstrate low-temperature ink-based fabrication of CuInS2-based photoelectrodes for hydrogen production capable of producing photocurrent densities as high as 8.8 mA.cm−2. In this process, molecular ink made of metal chlorides and thiourea dissolved in methanol was spin coated onto Mo-coated soda lime glass substrates. Samples were then placed on a hot plate (sample surface temperature: 250 °C) to induce CuInS2 formation and remove the solvent and by-products. No further processing, such as high temperature sulfurization, was performed. The CuInS2 films were then integrated as photocathode for hydrogen evolution by photoelectrodeposition of Pt nanoparticles. Photocurrent density of 0.4 mA.cm−2 at 0 V vs. RHE was detected from such electrodes. However, samples coated with CdS/ZnO/ITO overlayers forming heterojunction prior to Pt deposition exhibited significant improvement of the photocurrent density, reaching 8.8 mA.cm−2 at 0 V vs. RHE, highlighting the improved charge transfer by the p-n junction formed at the CuInS2/CdS interface. The charge transfer resistance of the CuInS2/CdS/ZnO/ITO-Pt photoelectrode was almost 5 times lower than that of the CuInS2-Pt photoelectrode as revealed by electrochemical impedance spectroscopy analysis. In addition, the onset potential was shifted by ca. 0.45 V toward the anodic direction, reaching 0.75 V vs. RHE. Solar cell made of identical structure (Mo/CuInS2/CdS/ZnO/ITO) showed power conversion efficiency of 2.1% with short-circuit photocurrent density and open circuit voltage of 7.4 mA.cm−2 and 820 mV, respectively.

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.

Vapor Phase Synthesis of SnS Facilitated by Ligand-Driven "Launch Vehicle" Effect in Tin Precursors.

Extraordinary low-temperature vapor-phase synthesis of SnS thin films from single molecular precursors is attractive over conventional high-temperature solid-state methods. Molecular-level processing of functional materials is accompanied by several intrinsic advantages such as precise control over stoichiometry, phase selective synthesis, and uniform substrate coverage. We report here on the synthesis of a new heteroleptic molecular precursor containing (i) a thiolate ligand forming a direct Sn-S bond, and (ii) a chelating O^N^N-donor ligand introducing a “launch vehicle”-effect into the synthesized compound, thus remarkably increasing its volatility. The newly synthesized tin compound [Sn(SBut)(tfb-dmeda)] 1 was characterized by single-crystal X-ray diffraction analysis that verified the desired Sn:S ratio in the molecule, which was demonstrated in the direct conversion of the molecular complex into SnS thin films. The multi-nuclei (1H, 13C, 19F, and 119Sn) and variable-temperature 1D and 2D NMR studies indicate retention of the overall solid-state structure of 1 in the solution and suggest the presence of a dynamic conformational equilibrium. The fragmentation behavior of 1 was analyzed by mass spectrometry and compared with those of homoleptic tin tertiary butyl thiolates [Sn(SBut)2] and [Sn(SBut)4]. The precursor 1 was then used to deposit SnS thin films on different substrates (FTO, Mo-coated soda-lime glass) by CVD and film growth rates at different temperatures (300–450 °C) and times (15–60 min), film thickness, crystalline quality, and surface morphology were investigated.

Effect of Cu-In-Ga Target Composition on Hybrid-Sputtered Cu(In,Ga)Se2Solar Cells

High-efficiency Cu(In,Ga)Se <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> (CIGSe) thin-film solar cells are typically fabricated by a multistage coevaporation process. The Cu-rich composition achieved during the second stage is known to favor the grain growth of the polycrystalline CIGSe film and has a beneficial effect on the solar cell performance. In this article, we analyze the effect of copper stoichiometry on the grain size of sputtered CIGSe absorbers and the efficiency of respective solar cells. CIGSe absorber layers were deposited on Mo-coated soda-lime glass substrates by pulsed hybrid reactive magnetron sputtering from Cu-poor and Cu-rich Cu-In-Ga targets and simultaneous Se evaporation. CIGSe films sputtered with the Cu-rich target show larger grain size and lead to better solar cell performance. Furthermore, we also introduce a two-stage process, which further increases the solar cell performance, consisting of an initial CIGSe layer deposited from the Cu-rich target followed by an indium-selenide postdeposition step. This two-stage process effectively eliminates the unwanted Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2-</sub> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> Se impurity phase and renders the otherwise required and toxic KCN etching unnecessary.

Phase development in RbInSe2 thin films – a temperature series

Rb, In and Se were deposited in a co-evaporation chamber at various substrate temperatures (TSub = 280°C, 350°C, 450°C, 550°C) on Mo coated soda-lime glass. It was found that the RbInSe2 crystal phase is already detectable for nominal TSub = 350°C. During calibrated in-situ high-temperature grazing incidence X-ray diffraction on the sample grown at the lowest temperature, crystallization of monoclinic RbInSe2 can be observed at 215°C ± 3°C. The morphology of the layers shows distinct differences for increasing TSub, while the elemental composition of the deposited thin films only exhibits minor changes. The deposited layers show a decrease of (X-ray) amorphous constituents and changes in the preferred crystal orientation of the RISe layer with increasing TSub. The influence of Na supply on the layer growth was investigated by applying a SiNxOy diffusion barrier layer in between the glass substrate and the Mo layer on half of the studied samples.

Improving the Cu2ZnSn(S,Se)4-Based Photovoltaic Conversion Efficiency by Back-Contact Modification

Back-contact modification using a 10-nm ZnS layer in CZTSSe-based solar cell can play a crucial role in improving photovoltaic conversion efficiency. An ultrathin layer of ZnS is deposited over Mo-coated soda lime glass substrate before depositing CZTSSe using sputtering. The crystal structure of deposited CZTSSe thin films over ZnS is recognized as (112)-oriented, polycrystalline in nature, and free from the presence of any secondary phases such as Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> (S,Se) or Zn(S,Se). The bandgap of CZTSSe thin films deposited over ultrathin ZnS is observed to increase from 1.49 (deposited over Mo directly) to 1.58 eV at room temperature, as determined by spectroscopic ellipsometry. In addition, numerical simulation has been performed using SCAPS software. The impact of ZnS layer has been simulated by using the defects in the absorber and at the interface of ZnS/CZTSSe. The simulated results have been validated with experimentally fabricated CZTSSe device. Simulated device with ZnS intermediate layer is observed to give rise to a photovoltaic conversion efficiency of 15.2%.

Effect of Na-doped Mo layer as a controllable sodium reservoir and diffusion barrier for flexible Cu(In,Ga)Se2 solar cells

To overcome the absence of sodium (Na) and to prevent undesired impurity diffusion from stainless steel (STS) substrates, a bi-layer molybdenum (Mo) structure consisting of a 1-μm-thick Mo and Na-doped Mo (Mo:Na) with variable thickness was utilized as the back contact layer in copper–indium–gallium–selenide (CIGS) solar cells. Na ions were supplied to the CIGS absorber layer from the Mo:Na layer, and the amount of Na ions was controlled by changing the thickness of Mo:Na layer. The Na doping to the CIGS layer is verified by the X-ray photoelectron spectroscopy (XPS) and the dynamic secondary ion mass spectroscopy (D-SIMS). The recombination process in the bulk CIGS and the CdS/CIGS junction has been analyzed by temperature dependent current density–voltage (J–V–T) measurement. The D-SIMS showed that the amount of Na ions in the CIGS layer grown on Mo/Mo:Na/STS is comparable with that in the conventional CIGS film deposited on Mo coated soda-lime glass. Moreover, the bi-layer Mo also acts as a diffusion barrier layer against the Fe atoms, which deteriorate the quality of CIGS. The higher content of Na ions and the lower content of Fe ions in the CIGS layer lowered the recombination activation energy, series resistance and ideality factor, leading to improved junction quality. As a result, the short circuit current density and power conversion efficiency of the CIGS on the Mo and 600-nm-thick Mo:Na were improved by 8.1 and 69.4%, respectively, compared with those of CIGS solar cells fabricated without a Mo:Na layer.

The preparation of Cu2ZnSnS4 thin film solar cell based on oxygen containing precursor

In this paper, we reported a new method to fabricate Cu2ZnSnS4 (CZTS) thin film solar cells. Oxygen containing precursor thin films were deposited on the Mo-coated soda lime glass (SLG) by sputtering ZnO, SnO2 and Cu targets. For getting higher quality CZTS thin films, the effects of different annealing temperatures of 380 °C, 480 °C, 580 °C and 650 °C on CZTS films were systematically investigated. The results showed that the optimum annealing temperature was 580 °C. Through optimizing the sulfurization process, phase-pure CZTS thin films with compact and large grains were obtained. Composition analysis showed that O was not detected after sulfurizing process which indicated all of O was replaced by S. And due to the stability of SnO2, the loss of tin can be avoided. In addition, ZnO not only can provide zinc sources, but also can decrease the thickness of MoS2 as a barrier layer. Finally, CZTS solar cells based on sputtering oxides targets were obtained and the preliminary fabricated CZTS thin film solar cells had an efficiency of 5.08%, with an open-circuit voltage of 645 mV, a short-circuit current density of 21.74 mA/cm2 and a fill factor of 36.23%.

Investigation on the properties of Cu 2 ZnSnSe 4 and Cu 2 ZnSn(S,Se) 4 absorber films prepared by magnetron sputtering technique using Zn and ZnS targets in precursor stacks

Cu2ZnSnSe4 and Cu2ZnSn(S,Se)4 absorber films were grown on soda lime glass and Mo-coated soda lime glass substrates by deposition of the precursor films via RF magnetron sputtering method in the stacking orders of Cu/Sn/Zn/Mo/SLG and Cu/Sn/ZnS/Mo/SLG using metallic Zn or binary sulfide ZnS targets and subsequently carrying out of selenization process. It was aimed to find out the effect of Zn or ZnS target types and the small amount of S originated from ZnS target material used in the deposition of precursor films on the structural, morphological, optical, and electrical characteristics of the films to be selenized. XRD and Raman spectroscopy analysis showed that the kesterite CZTSe structure was predominantly formed in both cases where Zn and ZnS targets were used. According to the EDX analysis, S content in the prepared film using ZnS target was only around 1.79 at%. This indicated that a considerable amount of S in the film was driven out during the selenization process. Scanning electron microscopy analysis revealed that ZnS target material contributed to the achievement of the absorber films with larger grain size. It was also determined that the thickness of the interfacial MoSe2 film between the absorber and Mo films decreased by using ZnS target in the precursor film. This was attributed to ZnS layer with a high melting point acting as a barrier layer over Mo film and retarding the diffusion of Se into the Mo film during the selenization process. In addition, the band gap energy values of the Cu2ZnSnSe4 and Cu2ZnSn(S,Se)4 films were found to be 1.18 and 1.28 eV, respectively.

Effect of Ge &amp; ZnO inter-layer on the properties of CZTSSe absorber layer

The use of intermediate layer between Mo and CZTSSe highly affects the properties of Cu 2 ZnSn(S x Se 1-x ) 4 (CZTSSe) absorber layer. The goal of the present work is to get a deeper insight into the beneficial effects of incorporation of an inter-layer between Mo and CZTSSe on absorber layer properties. In this work Ge and ZnO thin layer deposited on the different Mo coated Soda lime glass (SLG) substrates, then a thin layer of CZTS were printed by Doctor blade method, followed by Selenium deposition by thermal evaporation. Films were annealed at 450 °C for 20 min and its structural, optical and electrical properties were studied. The main purpose of this work is to study the variation in the properties of the absorber layer with and without an inter-layer. The crystallinity, conductivity, grain size and mobility of the film improves with Ge as an intermediate layer as compared to Mo or Mo/ZnO. The band gap decreases for Ge intermediate layer and slightly increases with ZnO as an intermediate layer. The Germanium layered film enhances the grain growth and crystallinity of the film as compared to Mo and Zinc Oxide layered. The changes observed in the film properties with the incorporation of Ge and ZnO inter-layer is discussed in the present paper.

Optimization of selenization parameters for fabrication of CZTSe thin film

Abstract For the formation of CZTSe films, selenization time and temperature play a crucial role in a material synthesis which in turn highly affects the properties of the films. In this work, Cu, Zn, Sn and Se were thermally-deposited sequentially on Mo coated soda-lime glass (SLG) substrates. For the formation of Cu2ZnSnSe4 (CZTSe) deposited films were annealed in a two-step process (first step 230 °C for 10 min and second step 450 °C for 5 min–30 min with 5 min interval) in Selenium (Se) atmosphere. The effect of selenization time on the structural, surface morphology, compositional, optical and electrical properties of the CZTSe films was studied. The formation of CZTSe phase is observed from XRD and Raman spectra. It was observed that with the increase in selenization time the CuSe binary phase present in the film suppressed gradually. The grain size, conductivity and mobility of the films increase whereas the band gap decreases with the increase in the hold time in the second step of selenization. The selenization time improves the properties of the films which can be suitable for solar cell applications. The study shows that optimum selenization time is essential to get a good quality CZTSe film. The device has been attempted for sample M6 and the best device obtained gives a conversion efficiency of 3.97%

Influence of Sulfurization Time on the Properties of Cu2ZnSnS4 Thin Films Deposited on Mo-coated Soda Lime Glass Substrates by Co-sputtering Technique

In this work, Cu2ZnSnS4 (CZTS) absorber films were prepared by sulfurization of co-sputtered precursor films at different time periods. The influence of sulfurization time on physical characteristics of the grown films was investigated in detail. The sulfurized CZTS films exhibited the characteristic diffraction peak of the kesterite phase corresponding to the (112) crystal plane, the main Raman mode of kesterite phase at around 337 cm−1 and Cu-deficient and Zn-rich composition. From the atomic force microscopy surface and cross-sectional scanning electron microscopy images, it was revealed out that the films were uniform, compact without any cracks and consisted of micron-sized and closely packed grains. In addition, the films showed tail-to-tail, band-to-tail and band-to-band transitions at around 1.41 eV (E1), 1.45 eV (E2) and 1.51 eV (E3), respectively. Secondary ion mass spectroscopy analysis showed that the sodium ions deeply diffused through the molybdenum layer into the CZTS film from the soda lime glass substrate for all samples. All of the films exhibited an optical band gap of around 1.4 eV, an absorption coefficient over 104 cm−1, p-type conductivity with a high concentration of free holes in the order of 1017-1018 cm−3 and low mobility in the range from 0.63 cm²/V.s to 8.11 cm²/V.s.

Influence of WSe2 buffer layer at back electrode on performance of Cu2ZnSn(S,Se)4 solar cells

CZTSSe-based solar cells with a structure of Al/ITO/ZnO/CdS/CZTSSe/p-WSe2/Mo (denoted as WSe2-CZTSSe solar cell) were prepared on the Mo-coated soda-lime glass (SLG) with a pre-sputtering metal tungsten (W) layer. Comparing with the conventional CZTSSe solar cell with a structure of Al/ITO/ZnO/CdS/CZTSSe/n-MoSe2/Mo (denoted as CZTSSe solar cell), the WSe2-CZTSSe solar cell shows a significant improvement in open-circuit voltage (VOC), short-circuit current density (JSC) and fill factor (FF), and so its power conversion efficiency (PCE) enhances. The largest enhancement of the PCE is from 4.13% of the CZTSSe solar cell to 5.45% of the WSe2-CZTSSe solar cell. The increased VOC and JSC are mainly due to the enhancement of photogenerated current density (JL) and decrease of reversion saturation current density (J0), while the increased FF is ascribed to the increase of shunt resistance (RSh). The influence mechanism of the WSe2 buffer layer on JL, J0 and RSh is also investigated in detail. Our results present a route of increment of PCE by reducing and even removing back contact barrier between CZTSSe and MoSe2 layers.

Single-step growth of high quality CIGS/CdS heterojunctions using Pulsed Laser Deposition

This work reports on the utilization of pulsed laser deposition (PLD) for the preparation of CdS thin films and CdS/Cu(In,Ga)Se2 heterojunction structures on soda-lime glass (SLG) and Mo-coated SLG substrates, respectively, under various process conditions. Single phase, stoichiometric and high optical quality CdS films are obtained at a fluence of 1.1 J/cm2 and at deposition temperatures of 200–400 °C. The results of this investigation were used to grow CdS on Cu(In,Ga)Se2/Mo/SLG. Both Cu(In,Ga)Se2 and CdS layers have been deposited sequentially using PLD without interrupting the deposition process. The influence of CdS deposition temperature on the properties of CdS/Cu(In,Ga)Se2 heterojunction has been extensively studied and is reported herein for the first time. Low series and high shunt resistances are obtained for the samples where CdS was grown at 200 and 300 °C. The CdS/Cu(In,Ga)Se2 diode grown at CdS deposition temperature of 300 °C exhibits the lowest ideality factor and leakage current, indicating the better quality of the diode. The results of this work demonstrate that high-quality CdS/Cu(In,Ga)Se2 diodes are obtained using pulsed laser deposition in a single-step growth process, eliminating the need for selenization of Cu(In,Ga)Se2 and the use of other growth techniques such as chemical bath deposition for CdS.

Sodium-assisted passivation of grain boundaries and defects in Cu2ZnSnSe4 thin films

The long stagnation of the photo-conversion efficiency of kesterites below 13% is a source of frustration in the scientific community. In this study, we investigated the effects of sodium on the passivation of grain boundaries and defects in Cu2ZnSnSe4 (CZTSe) grown on a soda-lime glass (SLG) and borosilicate (BS) glass. Because BS glass does not inherently contain sodium, we placed a thin layer of NaF between CZTSe and Mo. The composition of the samples is Cu-poor and Zn-rich. The distribution of sodium and its contributions to phase formation and defects were examined by cross-sectional energy-dispersive X-ray profiling, Raman scattering spectroscopy and imaging, surface potential and photoluminescence. From the experimental results, it can be strongly claimed that sodium ions segregate predominantly near the grain boundaries and reduce CuZn-related defects. These local surface imaging analyses provided the exact locations of the secondary phases. In particular, the photo-assisted scanning probe method enabled us to observe the changes in the optoelectrical properties of the thin films and the carrier behavior within the materials. Further studies with distinct alkali ions and optimal processing conditions will pave a way to improve the performance of kesterite solar cells.

Influence of Ge/(Ge+Sn) composition ratio in Cu2Sn1-xGexS3 thin-film solar cells on their physical properties and photovoltaic performances

Effect of Ge/(Ge + Sn) composition ratio of Cu2Sn1-xGexS3 (CTGS) films is examined. The CTGS films are fabricated by sulfurization of the 700-nm-thick Cu–SnS2/Ge stacked precursors on Mo-coated soda-lime glass (SLG) substrates. It is revealed that the thickness of Ge precursor (Ge thickness) from 0 to 420 nm enhances the Ge/(Ge + Sn) composition ratio in the CTGS thin films from 0 to about 0.58, thereby increasing bandgap energy (Eg) from approximately 0.97 (Cu2SnS3: CTS) to 1.23 eV (CTGS), respectively. Not only does Ge precursor act as Ge source to form the CTGS films but also it prevents the formation of undesirable MoS2 secondary phase. In addition, the CTGS solar cells with a structure of SLG/Mo/CTGS/CdS/ZnO/ZnO:Al/Ni/Al are fabricated with the Ge thickness from 0 to 420 nm. It is found that the optimized Ge thickness of 200 nm resulting in the Ge/(Ge + Sn) composition ratio of about 0.32 eliminates the excessive MoS2 secondary phase and increases the Eg, thereby increasing conversation efficiency (η) to 5.6% of the CTGS solar cell, higher than that (3.6%) of the CTS solar cell. However, the η is reduced when the Ge thickness over 200 nm because CTGS quality observed by Urbach energy is deteriorated and the conduction band offset at the CdS/CTGS interface demonstrates the large cliff type heterostructure, thus increasing the open-circuit voltage deficit.

Molybdenum incorporated Cu1.69ZnSnS4 kesterite photovoltaic devices with bilayer microstructure and tunable optical-electronic properties

Molybdenum (Mo) incorporated Cu1.69ZnSnS4 (CZTS) absorber has been deposited onto Mo-coated soda lime glass (SLG) by co-sputtering of Mo and non-stoichiometric quaternary compound targets. After sulfurization at 600 °C, Mo incorporation into CZTS was confirmed by X-ray diffraction (XRD) and secondary ion mass spectrometry (SIMS). From the observed shifts for the (1 1 2) and (2 2 0) peaks, both lattice parameters a and c of the CZTS unit cell were found to decrease with increasing Mo incorporation suggesting cationic substitution by Mo. The Mo incorporated CZTS has a bilayer microstructure in which the lower sub-layer adjacent to the substrate has a smaller grain size and higher porosity than the upper sub-layer. The lower sub-layer is also richer in Mo and has a graded Mo profile. Sheet resistance measurements on Mo incorporated CZTS films deposited on SLG and on quartz show resistivity that decreases with the amount of Mo in CZTS and Mo acts as an acceptor dopant. The energy band gap of CZTS on SLG increases from 1.38 eV to about 1.68 eV as a result of Mo incorporation and the absorbance of Mo incorporated CZTS is increased for wavelengths shorter than 600 nm. When Mo is co-deposited at the optimized DC sputtering power of 10 W, Mo incorporated CZTS/CdS solar cells attain a maximum power conversion efficiency (PCE) of 5.49% versus 1.63% for the reference device under 1 Sun AM 1.5 illumination. Device efficiency enhancement is due to back surface field, increased carrier concentration and reduced band tailing.

Investigation of carrier recombination of Na-doped Cu2SnS3 solar cell for its improved conversion efficiency of 5.1%

Na-doped Cu2SnS3 (CTS) solar cells are fabricated and their carrier recombination is examined. The CTS absorbers on Mo-coated soda-lime glass substrates are grown by the sulfurization of NaF/Cu–SnS2 (900 nm) precursors. The NaF thickness is varied from 0 to 100 nm to vary the Na content in the resulting CTS absorbers. It is disclosed that the large grain with the uniformity of the material distribution (Cu, Sn, and S) in the Na-doped CTS absorber is obtained. With optimal Na doping (NaF thickness of 60 nm), the open-circuit voltage deficit (VOC,def) is obviously reduced, whereas short-circuit current density deficit (JSC,def) is not varied much. The reduction of VOC,def is attributable to the decrease in the carrier recombination across the device. The conversion efficiency (η) is consequently increased to approximately 4.7%. However, with severe Na doping (NaF thickness of over 75 nm), the VOC,def is clearly increased owing to the increase in the carrier recombination, thereby reducing the η. This is occurs because the Sn2S3 and Na2S secondary phases near the surface of the CTS film are formed with the severe Na doping. To further increase the η, the JSC,def is reduced through the decrease in CdS buffer thickness. Ultimately, the 5.1%-efficient CTS solar cell is obtained with the Na-doped CTS absorber prepared with the optimal NaF thickness of 60 nm.

Effect of Annealing Process Pressure Over Atmospheric Pressure on Cu2ZnSn(S,Se)4 Thin Film Growth

Cu2ZnSn(S,Se)4(CZTSSe) thin film solar cells areone of the most promising candidates for photovoltaic devices due to their earth-abundant composition, high absorption coefficient and appropriate band gap. The sputtering process is the main challenge to achieving high efficiency of CZTSSe solar cells for industrialization. In this study, we fabricated CZTSSe absorbers on Mo coated soda lime glass using different pressures during the annealing process. As an environmental strategy, the annealing process is performed with S and Se powder, without any toxic H2Se and/or H2S gases. Because CZTSSe thin films have a very narrow stable phase region, it is important to control the condition of the annealing process to achieve high efficiency of the solar cell. To identify the effect of process pressure during the sulfo-selenization, we experiment with varying initial pressure from 600 Torr to 800 Torr. We fabricate a CZTSSe thin film solar cell with 8.24 % efficiency, with 435 mV for open circuit voltage(VOC) and 36.98 mA/cm2 for short circuit current density(JSC), under a highest process pressure of 800 Torr.

Improving the crystallization and carrier recombination of Cu2ZnSnS4 thin film deposited on Mo-coated soda-lime glass by extra sodium doping through solution process

In this paper an easy and mild solution-processed method is introduced to prepare extra sodium (Na) doped Cu2ZnSnS4 (CZTS) films on Mo-coated soda-lime glasses. Through this method, the Na-doping concentration can be adjusted at the range from 3.9% to 5.4% continuously. By extra Na doping through solution process, the grain size of CZTS particles was enlarged apparently without introducing any impurity phase. More excitingly, the photoluminescence (PL) spectrum indicates that high Na-doping concentration has the strong suppression ability on the band-gap recombination of CZTS films. The carrier lifetime is promoted from 2.1 ns to 2.83 ns. CZTS thin film solar cell with 4.8% Na-doping concentration shows the best performance.