Production Of Thin-film Solar Cells Research Articles

Systematic inspection on the interplay between MoNa-induced sodium and the formation of MoSe2 intermediate layer in CIGSe/Mo heterostructures

The critical impact of sodium-doped molybdenum (MoNa) in shaping the MoSe2 interfacial layer, influencing the electrical properties of CIGSe/Mo heterostructures, and achieving optimal MoSe2 formation conditions, leading to improved hetero-contact quality. Notably, samples with a 600-nm-thick MoNa layer demonstrate the highest resistivity (73 μΩcm) and sheet resistance (0.45 Ω/square), highlighting the substantial impact of MoNa layer thickness on electrical conductivity. Controlled sodium diffusion through MoNa layers is essential for achieving desirable electrical characteristics, influencing Na diffusion rates, grain sizes, and overall morphology, as elucidated by EDX and FESEM analyses. Additionally, XRD results provide insights into the spontaneous peeling-off phenomenon, with the sample featuring a ~ 600-nm MoNa layer displaying the strongest diffraction peak and the largest crystal size, indicative of enhanced Mo to MoSe2 conversion facilitated by sodium presence. Raman spectra further confirm the presence of MoSe2, with its thickness correlating with MoNa layer thickness. The observed increase in resistance and decrease in conductivity with rising MoSe2 layer thickness underscore the critical importance of optimal MoSe2 formation for transitioning from Schottky to ohmic contact in CIGSe/Mo heterostructures. Ultimately, significant factors to the advancement of CIGSe thin-film solar cell production are discussed, providing nuanced insights into the interplay of MoNa and MoSe2, elucidating their collective impact on the electrical characteristics of CIGSe/Mo heterostructures.Graphical

A comprehensive DFT + U investigation of electrical, optical, and structural properties of doped CsSnCl3 Perovskite: Unveiling optoelectronic potential

In the realm of advanced electrical and photovoltaic applications, inorganic metal halide perovskites (MHP) have captured attention. However, CsSnCl3, a notable member of MHPs, displays limited electro-optical potential due to its substantial bandgap and poor visible spectrum absorbance, which impedes its ability to achieve ideal optoelectronic efficiency. In this study, we used density functional theory (DFT) and the DFT + U technique to compute and investigate the structural, elastic, electrical, and optical properties of pure CsSnCl3 and its doped phases containing Ti, V, Cr, and Mn with different concentrations. Notably, this study represents the first utilization of DFT + U to simultaneously assess the band structure of both pure and doped CsSnCl3. Through meticulous alignment with experimental data and the derivation of a suitable Hubbard U correction value (6.5), our analysis reveals a refined band structure for pristine CsSnCl3. Critically, our research transcends conventional bandgap understanding, unlocking a profound connection between bandgap modulation and enhanced optoelectronic efficiency. Specifically, our systematic exploration uncovers a noteworthy enhancement in performance for various optoelectronic applications upon doping with V, Ti, Cr, and Mn, substantiating the practicality of our approach. Investigations into mechanical stability reveal that all doped samples exhibit a remarkable ductile nature, rendering them well-suited for thin-film solar cell production and other applications demanding stability and flexibility. By bridging the gap between theory and application, our study empowers researchers and industry professionals with actionable insights for selecting the most suitable doped compositions of CsSnCl3, ushering in an era of highly efficient and environmentally sustainable optoelectronic technologies.

Role of the substrates in the ribbon orientation of Sb2Se3 films grown by Low-Temperature Pulsed Electron Deposition

Antimony selenide (Sb2Se3) is a p-type semiconductor, considered as an excellent photovoltaic absorber for its high absorption coefficient in the visible region and a nearly optimal band-gap for single-junction solar cells. The simple binary composition, together with non-toxic and earth-abundant constituents make this material very promising toward industrial production of low-cost thin-film solar cells. Theoretical calculations and experimental data have confirmed that Sb2Se3 exhibits strong anisotropic optoelectronic properties, due to the presence of infinite covalent (Sb4Se6)n ribbons along the (001) direction, whereas weak van der Waals interactions occur between ribbons. In such anisotropic materials, electronic transport is strongly affected by crystal structure: when ribbons are aligned perpendicularly to the solar cell surface, a better collection of photogenerated current occurs, leading to larger photovoltaic conversion efficiencies.In order to understand the alignment mechanisms of ribbons, Sb2Se3 thin films were grown by Low-Temperature Pulsed Electron Deposition (LT-PED) technique at different temperatures (from 200 °C to 400 °C) on a variety of substrates, such as glass, molybdenum, CdS, Fluorine-doped Tin Oxide (FTO) and nanostructured ZnO. The structural and morphological characterization of the Sb2Se3 films, performed by out-of-plane and in-plane X-Ray Diffraction and micro-Raman spectroscopy, demonstrated that ribbon alignment along the surface normal is strongly dependent on the used substrate. The comparison between solar cells grown in substrate configuration on Mo and FTO, clearly demonstrates the influence of ribbon orientation on short-circuit current.

Energy, temperature, and deposition angle dependence of Cd and Te2 deposited on CdTe

Cadmium Telluride (CdTe) is an important material for the production of high-efficiency thin-film solar cells. While sputter deposition has been used to create CdTe-based solar cells, two other important methods of growth are close-spaced sublimation and vapor deposition. In these methods, the depositing clusters correspond to Cd atoms and Te2 dimers while the deposition energies are relatively low. In addition, depending on vapor pressure, deposition method, and target-substrate distance, deposition may occur at relatively large angles with respect to the substrate normal. Here we investigate the dependence of the attachment probability and deposition site for Cd and Te2 clusters deposited on Cd-terminated and Te-terminated (100) and (111) surfaces of zincblende CdTe on deposition conditions. In general, we find that the deposition of Cd atoms and/or Te2 dimers on the oppositely terminated surface leads to an attachment probability which is close to 1 and relatively independent of deposition conditions for both the (100) and (111) orientations. In contrast, deposition on the same terminated surface leads to a significantly lower attachment probability which generally decreases with increasing deposition angle, energy, and substrate temperature. Our results also indicate that deposition on the (111) surface leads to a significant excess Te sticking probability. In contrast, the excess Te attachment probability for deposition on the (100) surface is typically significantly smaller, and in some cases may even be negative. We also find, for both deposition on the (111) surface as well as opposite termination deposition on the (100) surface, that the dominant deposition mode corresponds to sitting on top of the surface which corresponds to growth of the next layer. In contrast, for same termination deposition on the (100) surface the dominant deposition mode corresponds to joining the first layer. These results imply that even for low deposition energies and substrate temperatures, deposition on the (100) surface is likely to create interstitials in the surface layer.

Influence of the Substrate Type on the Surface Morphology of Cu2ZnSnSe4 Thin Films

Investigations into the influence of the substrate type (a glass substrate with a molybdenum sublayer, tantalum and molybdenum foils) on the surface morphology of Cu2ZnSnSe4 thin films obtained by selenization of electrochemically deposited and preliminary annealed metallic precursors are presented. Metal foils are attractive for use as substrates of solar cells in both ground and space objects due to their light weight, flexibility, and the possibility of using the commercial roll-to-roll technology of film fabrication, leading to a reduction in the cost. At different stages of Cu2ZnSnSe4 film preparation, their surface morphology is studied by atomic-force microscopy and scanning electron microscopy in combination with energy-dispersive spectrometry. The metal substrate morphology is demonstrated to have an insignificant effect on the surface morphology of Cu2ZnSnSe4 films, indicating that flexible-foil substrates are promising for the production of thin-film solar cells.

Fabrication of Cd-free CuInSe2 solar cells using wet processes

CuInSe2 has become an attractive material for use in the production of thin-film solar cells. Recently, energy conversion efficiencies over 20% have been achieved by CuInSe2 solar cells created using vacuum processes. To reduce manufacturing costs, more recent efforts have focused on non-vacuum processes. In this study, we fabricated solar cells exclusively by wet processes. CuInSe2 absorption layers and In2S3 buffer layers were electrochemically or chemically deposited, and ZnO window layers were formed using solution-based chemical methods. The deposited CuInSe2 absorption layers were heat-treated to improve crystallinity. We deposited a Cd-free buffer layer of In2S3 using a chemical bath method on the CuInSe2 absorption layers, and then ZnO window layers were deposited by a solution-based process. With this system, we successfully fabricated CuInSe2 solar cells and obtained a cell efficiency of 2.38%.

Effect of Nanocrystal Size and Carbon on Grain Growth during Annealing of Copper Zinc Tin Sulfide Nanocrystal Coatings

Polycrystalline films were prepared by annealing coatings cast from colloidal dispersions of Cu2ZnSnS4 (CZTS) nanocrystals in sulfur vapor. This nanocrystal dispersion-based route is a promising potential low-cost approach for production of low-cost thin-film solar cells. We studied the effects of nanocrystal size, sulfur pressure, and carbon concentration on the microstructure development and grain growth during annealing. Coatings prepared from dispersions of CZTS nanocrystals with an average diameter of either 5 or 35 nm were annealed for 10–60 min at 600 °C in 50 or 500 Torr of sulfur. The CZTS nanocrystal size influenced both the rate and mechanism of grain growth. When coatings composed of 5 nm nanocrystals are annealed, abnormal grain growth forms micrometer-scale CZTS grains on the surface of the coating. In contrast, when CZTS coatings composed of 35 nm nanocrystals are annealed, grains grow uniformly via normal grain growth. Grain growth rates increased with sulfur pressure regardless of the nan...

Effects of different CdCl2 annealing methods on the performance of CdS/CdTe polycrystalline thin film solar cells

In this paper, the effects of different CdCl2 annealing methods, including vapor annealing and dip-coating annealing, on the performance of CdS/CdTe polycrystalline thin-film solar cells are studied. After annealing, the samples are lightly etched with 1% bromine in methanol to remove surface oxides. Both annealing methods give CdTe polycrystalline thin films with good crystallinity and complete structure. For solar cells containing the annealed CdTe films, cell efficiency first increases and then decreases as the concentration of CdCl2 solution used for dip-coating annealing increases, and the optimized CdCl2 concentration is 12%. The uniformity of the performance of all cells is analyzed by calculating the relative standard deviation for each parameter. The uniformity of cell performance can be improved dramatically by dip-coating annealing instead of vapor annealing. Most notably, an appropriate concentration of CdCl2 (12%) acts as a protective layer that is conducive to realizing uniform high-performance CdS/CdTe solar cells. According to the location of depletion regions, the CdTe films treated by dip-coating annealing show a relatively low doping concentration, except for the sample treated with a CdCl2 concentration of 6%, which is consistent with the changes of short-circuit current density of the cells. It is believed that these results can be applied to the large-scale production of CdTe polycrystalline thin-film solar cells.

Occupational exposure to arsenic and cadmium in thin-film solar cell production.

Workers involved in the production of Cd/As-based photovoltaic modules may be routinely or accidentally exposed to As- or Cd-containing inorganic compounds. Workers' exposure to As and Cd was investigated by environmental monitoring following a worst-case approach and biological monitoring from the preparation of the working facility to its decommissioning. Workplace surface contamination was also evaluated through wipe-test sampling. The highest mean airborne concentrations were found during maintenance activities (As = 0.0068 µg m(-3); Cd = 7.66 µg m(-3)) and laboratory simulations (As = 0.0075 µg m(-3); Cd = 11.2 µg m(-3)). These types of operations were conducted for a limited time during a typical work shift and only in specifically suited containment areas, where the highest surface concentrations were also found (laboratory: As = 2.94 µg m(-2), Cd = 167 µg m(-2); powder containment booth: As = 4.35 µg m(-2), Cd = 1500 µg m(-2)). The As and Cd urinary levels (As_u; Cd_u) were not significantly different for exposed (As_u = 6.11±1.74 µg l(-1); Cd_u = 0.24±2.36 µg g(-1) creatinine) and unexposed workers (As_u = 6.11±1.75 µg l(-1); Cd_u = 0.22±2.08 µg g(-1) creatinine). Despite airborne arsenic and cadmium exposure well below the threshold limit value (TLV) when the operation is appropriately maintained in line, workers who are involved in various operations (maintenance, laboratory test) could potentially be at risk of significant exposure, well in excess of the TLV. Nevertheless, the biological monitoring data did not show significant occupationally related arsenic and cadmium intake in workers and no significant changes or differences in arsenic and cadmium urinary level among the exposed and unexposed workers were found.

Ultra-thin film microcrystalline silicon with high deposition rate and its application in tandem silicon solar cells

Reducing production cost to accelerate the industrialization process of thin film solar cells (TFSCs) makes it urgently demanded to elevate the deposition rate and reduce the needed thickness of absorbers in addition to the prerequisite performance improvement. Based on very high frequency plasma enhanced chemical vapor deposition process with a low bombardment energy and large ion flux, ultra-thin, high-deposition-rate, and high-performing hydrogenated microcrystalline silicon (c-Si:H) single- and related hydrogenated amorphous silicon (a-Si:H)/c-Si:H double-junction TFSCs are developed in this study. By tuning various process parameters (silane concentration, power, and pressure), the deposition rates and electrical properties of c-Si:H materials are studied in detail. Device-level c-Si:H intrinsic materials with a deposition rate of 10.57 /s and photosensitivity of 7.54102 can be obtained when depositing with a silane concentration of 9%, a power of 70 W, and a pressure of 2.5 Torr. By further applying device-level high-deposition-rate c-Si:H intrinsic materials in c-Si:H single-junction TFSCs on magnetron-sputtered and wet-etched aluminum-doped zinc oxide (ZnO:Al) substrates with optimized surface morphologies and photoelectrical properties, and by combining advanced device designs, an initial conversion efficiency of 7.49% can be achieved for pin-type ultra-thin and high-deposition-rate c-Si:H single-junction TFSCs (the thickness values of intrinsic layers are 1.1~m). To further improve the conversion efficiency of TFSCs, pin-type a-Si:H/c-Si:H tandem TFSCs are fabricated by using n-a-Si/n-c-Si/n-nc-SiOx:H/p-nc-SiOx:H as the tunnel recombination junctions (TRJs), which, however, have unaddressed issues that the wide band-gap nc-SiOx:H materials with a low conductivity strongly reduce the recombination rate of carriers, thereby resulting in the photo-generated carriers accumulating near the TRJs, weakening the built-in electric field in the top sub-cells and leading to an open circuit voltage (Voc) loss in a-Si:H/c-Si:H tandem TFSCs up to 115~mV far above average values. By simultaneously inserting the p- and n-type narrow-gap c-Si:H materials, which are highly defective and narrower than the band gap of nc-SiOx:H materials, into the TRJs to implement the electrically lossless interconnection between the a-Si:H top and c-Si:H bottom sub-cells, the Voc loss is successfully reduced to 43~mV and an initial efficiency of 12.03% (Voc=1.48~eV, Jsc=11.67~mA/cm2, FF=69.59%) is achieved for ultra-thin pin-type a-Si:H/c-Si:H tandem TFSCs with a total thickness of 1.48~m, thus paving the way for the low-cost production of TFSCs.

Recycling of high purity selenium from CIGS solar cell waste materials

Copper indium gallium diselenide (CIGS) is a promising material in thin film solar cell production. To make CIGS solar cells more competitive, both economically and environmentally, in comparison to other energy sources, methods for recycling are needed. In addition to the generally high price of the material, significant amounts of the metals are lost in the manufacturing process. The feasibility of recycling selenium from CIGS through oxidation at elevated temperatures was therefore examined. During oxidation gaseous selenium dioxide was formed and could be separated from the other elements, which remained in solid state. Upon cooling, the selenium dioxide sublimes and can be collected as crystals. After oxidation for 1h at 800°C all of the selenium was separated from the CIGS material. Two different reduction methods for reduction of the selenium dioxide to selenium were tested. In the first reduction method an organic molecule was used as the reducing agent in a Riley reaction. In the second reduction method sulphur dioxide gas was used. Both methods resulted in high purity selenium. This proves that the studied selenium separation method could be the first step in a recycling process aimed at the complete separation and recovery of high purity elements from CIGS.

Effects of diethanolamine on sol–gel–processed Cu2ZnSnS4 photovoltaic absorber thin films

As a promising solar absorber, the Cu2ZnSnS4 compound has been popular recently for the production of green and economical thin-film solar cells owing to the abundancy and non-toxicity of all the constituents. In this study, we have produced Cu2ZnSnS4 films via the sol–gel technique. As a stabilizer, the effects of the diethanolamine on the properties of the films were investigated. The amount of diethanolamine significantly affected the crystal structure, crystallite sizes and phase purity of the films. X-ray diffraction and Raman spectroscopy analyses confirmed the formation of phase-pure CZTS films. It was found that the film produced by using 2ml of diethanolamine in sol exhibited pure CZTS phase, compact and dense morphology and enhanced photo-sensitivity. Light on/off current ratio of the n-Si/Cu2ZnSnS4 junction was found to be 47 under 100mW/cm2 of illumination. Electrical activation energies of the films were investigated and the variations were attributed to delocalized phonon states generating from the presence of other phases and lattice defects.

Numerical simulation of ultrafast expansion as the driving mechanism for confined laser ablation with ultra-short laser pulses

Recently, a so-called “directly induced” laser ablation effect has been reported, where an ultra-short laser pulse (660 fs and 1053 nm) irradiates a thin Mo film through a glass substrate, resulting in a “lift-off” of the irradiated layer in form of a thin, solid, cylindrical fragment. This effect provides a new and very energy-efficient selective structuring process for the Mo back electrode in thin-film solar cell production. To understand the underlying physical mechanisms, a 3D axisymmetric finite element model was created and numerically solved. The model is verified by a direct comparison of experimental and numerical results. It includes volume absorption of the laser pulse, heat diffusion in the electron gas and the lattice, thermal expansion of the solid phase and further volume expansion from phase transition to fluid and gas, and finally the mechanical motion of the layer caused by the resulting stress wave and the interaction with the substrate. The simulation revealed that irradiation of the molybdenum layer with an ultra-short pulse causes a rapid acceleration in the direction of the surface normal within a time frame of a hundred picoseconds to a peak velocity of about 100 m/s. The molybdenum layer continues to move as an oscillating membrane, and finally forms a dome after about 100 ns. The calculated strain at the edges of the dome exceeds the tensile stress limit at fluences that initiate the “lift-off” in experimental investigations. In addition, the simulation reveals that the driving mechanism of the “lift-off” is the ultrafast expansion of the interface layer and not the generated gas pressure.

Selenium adsorption on Mo(110): A first-principles investigation

Selenium adsorption on molybdenum surfaces is a relevant process in the production of thin-film solar cells, in particular as far as the formation of the layered compound MoSe${}_{2}$ is concerned. In this paper we investigate the energetics of Se adsorption on the (110) surface of molybdenum using first-principles calculations in the two limiting cases of low and high coverage, and we establish a comparison with the more extensively investigated case of sulfur adsorption at submonolayer coverage. The studied system provides the opportunity for testing the most crucial approximations, namely, the choice of the exchange-correlation functional and the pseudopotential generation. We find that semicore states of molybdenum have an influence on calculated surface energies and, to a lesser extent, on adsorption energies. We compare some more or less popular semilocal exchange-correlation functionals, including one recently proposed as an improvement for quasi-two-dimensional systems. The results show that the preferred adsorption site changes with coverage and suggest a strong variation of the adsorption energy with coverage.

Effects of the sulfurization temperature on sol gel-processed Cu2ZnSnS4 thin films

Abstract As a promising and alternative solar absorber material, the copper–zinc–tin–sulfide compound (Cu 2 ZnSnS 4 ) has been drawing attention in recent years for the production of cheap thin-film solar cells owing to the high natural abundance and non-toxicity of all the constituents, a tunable direct-band-gap energy and a large optical absorption coefficient. In addition, to overcome the problem of expensive vacuum-based methods, solution-based approaches are being developed for Cu 2 ZnSnS 4 deposition. In this study, we have produced Cu 2 ZnSnS 4 thin films via the sol–gel technique and subsequent sulfurization. The effects of the sulfurization temperature on the structural, morphological, compositional and optical properties of the films were investigated. X-ray diffraction and Raman spectroscopy analyses confirmed the formation of phase-pure CZTS films. The crystallinity of the films increased with an increasing sulfurization temperature. From the surface images and the results of the composition analysis, it was found that the films are uniform, composed of homogenously distributed grains and have compositions with Cu deficit. The values of the optical absorption coefficients for the films were found to be 10 4 cm −1 based on absorbance spectroscopy. The optical band-gap values were estimated to be between 1.32 and 2.27 eV depending on the sulfurization temperature.

Multiscale Modeling of CdTe Thin Film Deposition Process

ABSTRACTDeposition of semiconductor films is a key process for production of thin-film solar cells, such as CdTe or CIGS cells. In order to optimize photovoltaic properties of the film a comprehensive model of the deposition process should be build, which can relate deposition conditions and film properties. We have developed a multiscale model of deposition of CdTe film in close space sublimation (CSS) process. The model is based on kinetic Monte Carlo method on the rigid lattice, in which each site can be occupied by either Cd or Te atom. The model tabulates the energy of the site as a function of its local environment. These energies were obtained from first-principles calculates and then approximated with analytical formulas. Based on determined energies of each site we performed exchange (diffusion) processes using Metropolis algorithm. In addition the model included adsorption and desorption processes of Cd and Te2 species. The results of the model show that a steady-state structure of the surface layer is formed during film growth. The model can reproduce transition from film deposition to film etching depending on external conditions. Moreover, the model can predict deposition rates for non-stoichiometric gas compositions.

High deposition rate processes for the fabrication of microcrystalline silicon thin films

Abstract The increase of deposition rate of microcrystalline silicon absorber layers is an essential point for cost reduction in the mass production of thin-film silicon solar cells. In this work we explored a broad range of plasma enhanced chemical vapor deposition (PECVD) parameters in order to increase the deposition rate of intrinsic microcrystalline silicon layers keeping the industrial relevant material quality standards. We combined plasma excitation frequencies in the VHF band with the high pressure high power depletion regime using new deposition facilities and achieved deposition rates as high as 2.8 nm/s. The material quality evaluated from photosensitivity and electron spin resonance measurements is similar to standard microcrystalline silicon deposited at low growth rates. The influence of the deposition power and the deposition pressure on the electrical and structural film properties was investigated.

Transparent Conducting Oxides—An Up-To-Date Overview

Transparent conducting oxides (TCOs) are electrical conductive materials with comparably low absorption of electromagnetic waves within the visible region of the spectrum. They are usually prepared with thin film technologies and used in opto-electrical apparatus such as solar cells, displays, opto-electrical interfaces and circuitries. Here, based on a modern database-system, aspects of up-to-date material selections and applications for transparent conducting oxides are sketched, and references for detailed information are given. As n-type TCOs are of special importance for thin film solar cell production, indium-tin oxide (ITO) and the reasonably priced aluminum-doped zinc oxide (ZnO:Al), are discussed with view on preparation, characterization and special occurrences. For completion, the recently frequently mentioned typical p-type delafossite TCOs are described as well, providing a variety of references, as a detailed discussion is not reasonable within an overview publication.

Novel concept for laser patterning of thin film solar cells

AbstractLasers are increasingly being used as an efficient and reliable tool in the production of solar cells and solar modules. Particular interest exists in thin‐film photovoltaics, where laser structuring is aimed to realize appropriate monolithic serial interconnection. A novel concept successfully demonstrated complete laser structuring by application of short nanosecond laser pulses with a single, visible wavelength. These results promise further simplification and flexibility to thin film solar cell production.

Research on Sustainable Function Innovation Based on TRIZ

Based on the concept of front-end prevention, the demand evolution, technology evolution, function evolution, effects in TRIZ (Teoriya Resheniya Izobreata-telskikh Zadatch, Theory of Inventive Problems Solving) and sustainable functional innovation are integrated. The key enabling technologies for sustainable function innovation are studied, then innovation process model of for sustainable function innovation are formed. Finally, the CdTe thin film solar cell production line is taken as an example to validate the effectiveness of the above model.