CZTSe Solar Cells Research Articles

Suppressing the formation of double‐layer in Cu 2 ZnSnSe 4 ( CZTSe ) absorber layer by facile heating process through nontoxic selenium atmosphere

The Cu2ZnSnSe4 (CZTSe) absorber layer is typically prepared by post-selenization with a metal precursor. In the process of selenization, the loss of SnSex is a common phenomenon, resulting in both an atomic- ratio change and double-layer distribution of the absorber layer. This change affects the film properties. Additionally, excessive deviation from stoichiometry causes the formation of secondary-phase compounds. Moreover, the double-layer distribution reduces the carrier transport between the Mo back electrode and the CZTSe absorber film, inhibiting the effectiveness of the CZTSe solar cell. To address these problems, this study used CuxSe and ZnxSn1−x targets as the sputtering target materials to reduce the loss of SnSex during the selenization of precursor films. In addition, the effect of heating rate on the atomic ratio of the absorber layer was explored by adjusting the heating rate, which is one of the selenization parameters. The results showed that faster heating rates reduced the loss of SnSex, adjusted the Zn/Sn ratio in the absorber layer, and decreased ZnSe-related defects. In this way, the double-layer distribution was improved, air holes were reduced, and crystal structure characteristics of the films were enhanced. Photoluminescence (PL) spectroscopy showed that the signal of the ZnSe-related defect decreased, and the band tail effect became insignificant. The CZTSe absorber layer fabricated under different heating rates is used to prepare the CZTSe solar cell with a photoelectric conversion efficiency ranging from 0.51% to 5.6%.

Towards High-Efficiency CZTSe Solar Cells Through the Optimization of the p-MoSe2 Interfacial Layer

This paper reports the impact of the p-MoSe2 transition metal dichalcogenide as an interfacial layer between the CZTSe absorber and Mo back contact in the CZTSe solar cells. Here, the solar cell capacitance simulator (SCAPS-1D) is employed. The I-V characteristic demonstrated a higher slope in comparison to CZTSe solar cell without considering the interfacial layer. The results show that the p-MoSe2 layer benefits the CZTSe/Mo hetero contact by mediating the quasi- ohmic back contact of the CZTSe solar cell. Accordingly, the conversion efficiency improves from 16.17 % to 23.47 %. To investigate the effect of the p-MoSe2 layer, various performance parameters such as open-circuit voltage (Voc), short circuit current (Jsc), fill factor FF, and efficiency t] were explored at a wide range of thicknesses, bandgap energies, and the carrier concentration. The results revealed that a thickness of the interfacial layer less than 70 nm would cause deterioration of overall cell performance. This is because a low thickness of p-MoSe2 creates high barriers at the CZTS/p-MoSe2 and p-MoSe2/Mo interfaces, which impedes the drift process of photogenerated holes. Additionally, increasing the acceptor carrier concentration doping (NA) above 1017 cm3 results in an improved cell performance due to the enhanced band alignment at the back contact. The obtained values of the Voc and Jsc are 0.74 V and 42.6 mA/cm2, respectively.

Numerical analysis of the role of p-MoSe2 interfacial layer in CZTSe thin-film solar cells using SCAPS simulation

This work aims to report on the effect of p-MoSe2 transition metal dichalcogenide as an interfacial layer between the CZTSe absorber and Mo back contact in the CZTSe solar cells, using the solar cell capacitance simulator (SCAPS-1D). The results demonstrated that the p-MoSe2 layer benefits the CZTSe/Mo heterojunction by mediating the favourable quasi-ohmic contact to the CZTSe solar cell, which is revealed by a higher J–V characteristic slope and conversion efficiency improved from 16.17% to 25.19%. Various performance parameters such as open-circuit voltage (Voc), short circuit current (Jsc), fill factor (FF), and power efficiency (η) at a wide range of different layer parameters like thicknesses, bandgap energies, and carrier concentration (NA) were studied in detail. The results show that when the thickness of the MoSe2 interfacial layer is less than 65 nm, it causes a deterioration of overall cell performance. This is ascribed to the impedes of the drift of the photogenerated holes due to the increment of the barrier heights at the CZTSe/MoSe2 and MoSe2/Mo interfaces. Additionally, increasing the NA above 1017 cm−3 improves cell performance due to the enhanced band alignment at the back contact. The effect of the series resistance (Rs) on the CZTSe solar cell is also investigated. The obtained results show that by increasing the Rs from 1 to 5 Ω cm2, the efficiency decreases from 25.19% to 16.79% of the CZTSe solar cell using the MoSe2 layer. Finally, the impact of the device operating temperature is explored in the range from 250 K to 465 K. We noticed a drop of ~ 10% in η, from 26.80% to 15.89%, in the above range, due to the escalating reverse saturation current associated with high temperature.

Hole Transport Layer based on atomic layer deposited V2Ox films: Paving the road to semi-transparent CZTSe solar cells

This work explores the use of very thin transparent vanadium oxide films deposited by atomic layer deposition (ALD) technique as hole transport layer for CZTSe solar cells as alternative of opaque molybdenum based contacts. Contact resistivity between the CZTSe absorber and the ALD V2Ox contact was measured. In order to improve contact quality, a cleaning bath using hydrofluoric acid (HF) dip, was also analyzed and its influence on kesterite surface was studied. Elementary material characterization and composition analysis of the V2Ox layers was performed. Contact quality was assessed yielding contact resistivity values below 9 and 30 mΩcm2 for ALD and thermal evaporated V2Ox films respectively.The proposed ALD V2Ox based hole transport layer was deposited onto a glass covered with a transparent conductive oxide forming part of the rear contact scheme of a vertical CZTSe solar cell with a conventional ITO/CdS stack as electron transport layer. The impact of subsequent thermal post-annealing treatments in the cell performance was also analyzed yielding efficiency up to 3.9% on a semi-transparent CZTSe solar cell without any additional optimization process. In this way, a CZTSe solar cell with both transparent electrodes has been demonstrated paving the way to obtain in the future high efficiency bifacial and/or semitransparent Building –integrated photovoltaic devices.

In Situ Electrochemical Treatment Evoked Superior Grain Growth for Green Electrodeposition-Processed Flexible CZTSe Solar Cells.

Flexible Cu2ZnSnSe4 (CZTSe) solar cells gradually attract much attention due to their low-cost, lightweight, and environmentally friendly features. However, the efficiency of flexible CZTSe solar cells obtained through the nonvacuum green electrodeposition process remains sluggish (3.82%), far away from that obtained from other methods (∼10% by magnetron sputtering). Herein, a championed 6.33% efficiency of flexible CZTSe solar cells prepared by the electrodeposition process is achieved through an in situ electrochemical treatment (ET) process. It is found that the ET process drives the formation of a thin MoOx layer, evoking a series of beneficial results, thus accounting for an enhancement in photovoltaic performance. With the ET process, the MoSe2 thickness is compressed and Cu- and Sn-related undesirable defects/secondary phases are inhibited, leading to improved film quality. Additionally, it prolongs the depletion region width and minority lifetime, accelerates the charge separation and collection, relieves the band tails, and favorably reverses the band bending from downward to upward at/near grain boundaries. With these effects, the efficiency increases from 4.21% to 6.33%, far beyond the highest reports on electrodeposited flexible CZTSe solar cells. Our findings offer a promising way to improving Mo foil-based flexible devices and mark a significant breakthrough for the development of electrodeposition-processed flexible CZTSSe-based solar cells.

Optimization of Si (core)/CZTS/CZTSe (shell) nanowire array for solar cell

We present an optical simulation of a solar cell employing core (Si) /shell (Kesterite Cu2ZnSnS4 (CZTS) or/and Cu2ZnSnSe4 CZTSe) vertically-aligned nanowire array. The method of the simulation is rigorous coupled wave analysis. In the first stage, we studied the case where the shell is composed of only CZTS or CZTSe. A larger absorptance of CZTSe led to a larger value of the ideal short circuit current (41 mA/cm2) in the case of CZTSe solar cell than in the case of CZTS solar cell (24 mA/cm2). In the second stage, to avoid the heat losses in CZTSe solar cell without reducing the current, we proposed a shell composed of a 3 µm of CZTS in the upper part and a 6 µm of CZTSe in the lower part. The maximum ideal current value in this structure is almost twice as large as that of a planar solar cell with the same amounts of used materials. Furthermore, the variation of this maximal ideal current with the incident angle of the sunlight shows that the investigated solar cell still has good performance as long as the incident angle doesn’t exceed 60°.

Dominant recombination path in low-bandgap kesterite CZTSe(S) solar cells from red light induced metastability

Hetero-junction kesterite Cu2ZnSn(S,Se)4 solar cells with low bandgap obtained from three different methods of fabrication were exposed to red light illumination, and the changes observed in their electronic properties due to this exposure were studied via open circuit voltage transients, admittance spectroscopy, capacitance voltage profiling techniques, and SCAPS simulation fits to experimental data. The results from the aforementioned techniques, in combination with temperature-dependent current voltage analysis, can be used to reveal the dominant Shockley–Read–Hall recombination path at open circuit voltage. We also derived analytical expressions for the activation energy of the saturation current density and the diode quality factor for the specific case of a solar cell device that has no type inversion at the absorber/buffer interface and is limited by interface recombination in the open circuit condition. It is found that the dominant recombination pathway for the low bandgap Cu2ZnSn(S,Se)4 solar cells under consideration is located in the space charge region and not at the absorber/buffer interface.

Oxygen Promotes the Formation of MoSe2 at the Interface of Cu2ZnSnSe4/Mo.

The contact, and thus the hole collection between Cu2ZnSnSe4 (CZTSe) and Mo, is a crucial issue to improve the performance of CZTSe solar cells. In this work, a method to improve the back contact is explored by spraying Na3PO4 on the surface of the Mo back contact. With the O provided from Na3PO4, extra MoO2 and MoO3 are formed at the surface of the back contact, and partial MoO2 is transformed into MoSe2 under high Se2 partial pressure during the selenization process. The formation of MoSe2 progresses from dispersed spots to a continuous layer but not from the reaction between CZTSe and Mo. Although a thick MoSe2 layer is formed, the CZTSe device performance increases from 7.2% to 8.3% on average. This study affords new insight into the formation of MoSe2, thus deeply strengthening the understanding of the back contact of kesterite solar cells and of two-dimensional chalcogenide devices.

Efficiency enhancement of CZTSe solar cell using CdS(n)/(AgxCu1–x)2ZnSnSe4 (p) /Cu2ZnSnSe4 (p+) structure

Direct bandgap Cu2ZnSnSe4 (CZTSe) material is a promising absorber for thin film photovoltaics due to its affordable production cost and ecofriendly constituents. However, bulk defects, small grain size, short minority carrier lifetime and band bending at CZTSe/Mo (back contact) interface limit the performance of CZTSe solar cells. To overcome these issues, we design a single junction CdS(n)/ (AgxCu1–x)2ZnSnSe4 (p) /Cu2ZnSnSe4 (p + ) solar cell where we use (AgxCu1–x)2ZnSnSe4 (ACZTSe) as the main absorber layer. We have chosen the carrier density of each layer in a such way that ACZTSe becomes depleted and generated minority are collected efficiently. In our design, we utilize CZTSe as the back surface field layer to prevent surface recombination and indium doped tin oxide (ITO) as the back electrode to avoid band bending and increase the open circuit voltage. Additionally, we optimize the thicknesses of different layers and achieve a maximum efficiency of 18.63% including Shockley-Read-Hall, radiative and surface recombination mechanisms. The photo conversion efficiency (PCE) of our designed solar cell is 6% higher (12.6% vs 18.63%) than that of the best reported selenium rich CZTSe solar cell. The design concept proposed in this work would help in harvesting solar energy efficiently from next generation CZTSe solar cells.

Defect passivation in Cu2ZnSnSe4 thin-film solar cells by novel sodium doping

Sodium (Na) alkali doping is one of the effective ways to improve Cu2ZnSnSe4 (CZTSe) device performance by passivating detrimental native defects caused by off-stoichiometric composition and Cu–Zn cationic disordering. Various methods to incorporate Na in CZTSe films have been considered to realize the ideal distribution of Na in CZTSe films. Na content, regardless of Na incorporation method, is significantly increased in bulk CZTSe. Interestingly, when a NaF precursor is supplied after CZTSe film growth, the surface Na content is slightly increased, resulting in improved device performance. For the first time, a sodium bifacial treatment was employed to obtain an optimal profile of Na in CZTSe films. Using this novel route for Na doping, the photovoltaic (PV) device exhibited a maximum efficiency of 6.02%, which was higher than that compared to CZTSe devices with single Na doping and CZTSe device with Na diffused from soda-lime glass. According to defect analyses, the improved device performance is associated with a reduction in the defect density from 1.1 × 1016 (without Na doing) to 5.7 × 1014 cm−3 (with optimal Na profile). These results indicate that the proposed bifacial treatment method is a desirable means to fabricate high-efficiency, flexible CZTSe solar cells.

Facile Sb2Se3 and Se co-selenization process improves the performance of Cu2ZnSnSe4 solar cells

Selenization is effective to fabricate high-efficiency kesterite Cu2ZnSnSe4 (CZTSe) solar cells that facilitates the composition modification, crystallization enhancement, and bandgap adjustment. The incorporation of Sb into CZTSe absorbers can further boost the device efficiency mainly due to promoting the grain growth of CZTSe absorber. Here we report a Sb2Se3 and Se co-selenization process that significantly improves the quality of CZTSe absorber layers. This strategy enables the increase of CZTSe grain size and elimination of pinholes. We find that Sb is uniformly distributed in the absorber layer. When the Sb/(Cu + Zn + Sn) ratio is tuned to 6.67‰, the CZTSe solar cell exhibits the best device performance with an efficiency up to 9.64%, over 40% higher than the traditional selenization process. Our work provides a new route for enhancing the device efficiency of CZTSe solar cells.

A study of electrical and optical characteristics of CZTSe solar cell using Silvaco Atlas

This work represents the modeling and simulation of a CZTSe solar cell using the simulation software Silvaco Atlas. This simulation gives prominent results on the electrical and optical behavior of the CZTSe solar cell. In the physical structure of the cell, Indium Tin Oxide (ITO) and ZnO were used as the transparent conducting layer and the window layer respectively. The simulation study gives judicious results as open-circuit voltage (Voc) of 0.45 V, Short Circuit Current Density (Jsc) of 0.044 A/cm2, Fill Factor (FF) of 62.7%, Photon Conversion Efficiency (PCE) of 12.2%. The photon response characteristics of the solar cell validate the External Quantum Efficiency and the spectral response nature. The simulated CZTSe solar cell gives good results on its overall performance.

Modeling of CZTSSe solar photovoltaic cell for window layer optimization

Large and long-term future development of solar cells requires abundant non-toxic material like silicon. CZTSSe has emerged as next-generation solar material with an excellent candidate having better performance than previously studied compounds. This material is a non-toxic material available on earth that shows an acceptable bandage for showing eminent performance in the field of solar cells. The effect of different window layers on the electrical parameters of the solar cell has been investigated in present work. The thickness of the absorber layer, the window layer, the buffer layer and the doping concentration of absorber and buffer layer have been examined for the device structure Al: ZnO / TiO2 / ZnMgO / ZnO / CdS / CZTSSe / Mo of the solar cell. The present study also reveals that Al: ZnO is a better choice for the manufacturing of window layer in CZTSe solar cells. The solar cell parameters such as doping concentration, thickness and temperature have been optimized in the present study. The use of optimum values of solar cell parameters results in maximum optimized efficiency. The numerical simulation in this work presents a new approach to enhance the conversion efficiency of the CZTSSe solar cell. The proposed device structure may assist for experimental work. It is also expected that the present findings will be of great interest to experimentalists working in this field.

Sustainable Cu2ZnSnSe4 photovoltaic cells fabricated with a sputtered CdS buffer layer

AbstractIn this study, the effect of the Cu concentration on the characteristics of the Cu2ZnSnSe4 (CZTSe) absorber layers and solar cells was systematically analyzed by postselenization of the evaporated precursor deposits. The results demonstrated that an increase in the copper concentration of the precursor linearly increased the Cu content in the final CZTSe thin‐film formation. This significantly increased the particle size and improved the re‐evaporation loss of the SnSe, thus improving the solar cell characteristics. However, a further increase in the Cu concentration reduced the quality of the absorber layer and formed either CuxSe or CTSe secondary phases, which was detrimental to the solar cell characteristics. Here, we introduce a sputtered CdS buffer layer for the CZTSe solar cells. These findings offer new research directions for solving the persistent challenges in the chemical bath deposition (CBD) of the CdS in the CZTSe solar cells.

Nanoscale Surface Electrical Properties Tailored by Room‐Temperature Sulfurization for High‐Efficient CZTSe Solar Cells

AbstractSurface sulfurization can tailor the energy band alignment between p–n heterojunction for the kesterite‐structured Cu2ZnSnSe4 (CZTSe) solar cells. However, the traditional high‐temperature sulfurization process result in the decomposition of kesterite film and thus introducing deep defects. Room‐temperature surface sulfurization, which do not introduce new deep defects during the sulfurization process, is a good method for sulfurization. Combined by different experimental techniques, in this study, it is found that CZTSe film etched by concentrated ammonia can not only tailor the surface nanoscale composition, but also make CZTSe film to expose more crystallographic sites for the successful surface sulfurization. The conductivity of grains and grain boundaries for the absorber layer is improved, the minority carrier lifetime is increased, and the interface band alignment is modified by reducing the conduction band offset successfully after following (NH4)2S vapor treatments, which drive the improvement of the open‐circuit voltage (VOC) of the solar cell from 376 to 430 mV. This work can direct the surface bandgap engineering with nontraditional sulfurization to further enhance the performance of kesterite‐based thin film solar cells as well as other Se‐ or S‐containing solar cells.

A Novel Metal Precursor Structure for Electrodepositing Ultrathin CIGSe Thin-Film Solar Cell with High Efficiency.

The two-step process of electrodeposition and selenization is one of the most effective methods for producing CIGSe and CZTSe solar cells at a low cost. However, it is difficult to prepare the ultrathin CIGSe absorber by electrodeposition due to the nonuniform deposition of Cu on the Mo substrate. In this study, Cu was deposited on a Sb film instead of a Mo film, and the 3D growth mode of Cu was changed. Uniform and smooth ultrathin Cu films were fabricated on the Sb film using a pulse frequency over a range from 1000 to 10,000 Hz and a pulse current density ranging from 31.25 to 62.5 mA/cm2. Owing to the improved uniformity of Cu/In/Ga films, the thickness of the CIGSe absorber was reduced from 2 to 0.36 μm with Sb incorporation. In addition, the effects of Sb-doping on the CIGSe absorbers and the device performance were investigated. The crystallinity of the CIGSe films was improved, and the interface recombination of the solar cells was reduced by Sb incorporation. Ultimately, CIGSe thin-film solar cells with efficiencies of 5.25 and 11.27% were obtained with CIGSe absorber thicknesses of 0.36 and 1.2 μm, respectively.

Over 10% Efficient Pure CZTSe Solar Cell Fabricated by Electrodeposition with Ge Doping

The fabrication of kesterite CZTSe solar cells via an electrodeposition method provides an attractive approach for the low‐cost and environment‐friendly energy supply, yet the highest conversion efficiency for such solar cells (around 9%) is still far away from the highest efficiency of Cu‐based kesterite solar cells. Herein, a 10.54% efficient CZTSe solar cell (0.28 cm2 active sized area, without an antireflection layer) is developed by introducing electrodeposited Cu–Ge alloy layer at the bottom of metal precursor. It is found that the presence of Ge element within the bottom of the film can promote downward diffusion of Sn element. Consequently, the distribution of Sn is relatively homogeneous during the annealing process; thus, the formation of undesirable defect clusters is inhibited and the band alignment of the CdS/CZTSe interface is optimized. As a result, the conversion efficiency of CZTSe thin‐film solar cells is increased from 6.74% to 10.54%, which is the highest efficiency reported for electrochemically fabricated CZTSe solar cells.

Simulation of CZTSSe single solar cells by AFORS-HET software

In this paper, this sthdy simulated photovoltaic characteristics of single heterojunction solar cell with Cu2ZnSnS4 and Cu2ZnSnSe4 absorber layer numerically using the AFORS-HET program .n-CdS/ZnO double buffer layer is used for hetrostructure interfaces with the absorber layer. The cell performance is investigated against variation of different absorption layer properties such as thickness, carrier concentration. The mixed zinc and cadmium sulphide (Cd1-X Zn X S) is hired as buffer layers and reseach of the effect its thickness. CdS was selected a buffer because it improves the interface with absorbent CZTSSe and has a lofty sending in the blue wavelength. at thickness =1 μm and acceptor concentration (Na=7.9×1015 cm-3) ,a maximum efficiency (η=11.9%) is provided with an open-circuit voltage (Voc=688mv), short-circuit current (Jsc=24.6 mA.cm-2) and fill factor (FF =70.8 of the CZTS solar cell, and Voc=(597 mv), Jsc= (41.7mA.cm-2), FF = (81.2 %) and η= (20.2%) of the CZTSe solar cell.

Developing highly crystalline, single-phase and copper-poor Cu2ZnSnSe4 nanoparticles for solar cell application

In this study, we report the synthesis of Cu(Zn,Sn)Se2 (CZTSe) nanoparticles by hot-injection method for application to the absorber layer in solar cells. The composition of elements in the CZTSe nanoparticles depends mainly on the injection speed of the Se precursor. By controlling the injection speed, we obtained complete single-phase CZTSe nanoparticles with high crystallinity and copper-poor composition. The nanoparticle diameter mainly ranged from ~ 7 nm to 18 nm. The obtained CZTSe nanoparticles were used to fabricate a light absorber layer in the CZTSe solar cells. The cell exhibited performance, with short-circuit current density of ~ 30.8 mA/cm2, open-circuit voltage of 0.39 V, fill factor of 0.47 and conversion efficiency of 5.8%.

Investigation of low intensity light performances of kesterite CZTSe, CZTSSe, and CZTS thin film solar cells for indoor applications

Three kesterite thin-film solar cells, Cu2ZnSnSe4 (CZTSe), Cu2ZnSn(S,Se)4 (CZTSSe), and Cu2ZnSnS4 (CZTS), and based on low light intensity measurements, examined the possibility of using kesterite devices for indoor applications.