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Cu2ZnSnSe4 (CZTSe) nanoparticles (NPs) were successfully synthesized via a solvothermal method. Their structural, compositional, morphological, optoelectronic, and electrochemical properties have been characterized by X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), Field-emission scanning electron microscopy (FE-SEM), transmission electron microscope (TEM), UV–vis absorption spectroscopy, and electrochemical impedance spectroscopy (EIS) techniques. Porosimetry and specific surface area in terms of the Brunauer–Emmett–Teller (BET) technique have also been studied. XRD indicates the formation of a polycrystalline kesterite CZTSe phase. Raman peaks at 173 and 190 cm−1 confirm the formation of a pure phase. TEM micrographs revealed the presence of nanoparticles with average sizes of ~90 nm. A BET surface area of 7 m2/g was determined. The CZTSe NPs showed a bandgap of 1.0 eV and a p-type semiconducting behavior. As a proof of concept, for the first time, the CZTSe NPs have been used as a visible-light-driven photocatalyst to Congo red (CR) azo dye degradation. The nanophotocatalyst material under simulated sunlight results in almost complete degradation (96%) of CR dye after 70 min, following a pseudo-second-order kinetic model (rate constant of 0.334 min−1). The prepared CZTSe was reusable and can be repeatedly used to remove CR dye from aqueous solutions. [ABSTRACT FROM AUTHOR]

Cu2ZnSnSe4 (CZTSe) nanoparticles (NPs) were successfully synthesized via a solvothermal method. Their structural, compositional, morphological, optoelectronic, and electrochemical properties have been characterized by X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), Field-emission scanning electron microscopy (FE-SEM), transmission electron microscope (TEM), UV–vis absorption spectroscopy, and electrochemical impedance spectroscopy (EIS) techniques. Porosimetry and specific surface area in terms of the Brunauer–Emmett–Teller (BET) technique have also been studied. XRD indicates the formation of a polycrystalline kesterite CZTSe phase. Raman peaks at 173 and 190 cm−1 confirm the formation of a pure phase. TEM micrographs revealed the presence of nanoparticles with average sizes of ~90 nm. A BET surface area of 7 m2/g was determined. The CZTSe NPs showed a bandgap of 1.0 eV and a p-type semiconducting behavior. As a proof of concept, for the first time, the CZTSe NPs have been used as a visible-light-driven photocatalyst to Congo red (CR) azo dye degradation. The nanophotocatalyst material under simulated sunlight results in almost complete degradation (96%) of CR dye after 70 min, following a pseudo-second-order kinetic model (rate constant of 0.334 min−1). The prepared CZTSe was reusable and can be repeatedly used to remove CR dye from aqueous solutions.

One of the new materials for next-generation thin film solar cells is Cu 2 ZnSnSe 4 (CZTSe). However, achieving a single-phase CZTSe compound remains a challenge. This study describes the development of Cu 2 ZnSnSe 4 thin films through the sequential deposition of stacked films of non-stoichiometric Cu 2 SnSe 3 (CTSe) and ZnSe by magnetron sputtering. The structural, morphological, and electrical properties as well as the surface chemistry of the films were investigated and compared depending on the growth sequence of the thin films. By using Raman spectroscopy and grazing incidence X-ray diffraction, the tetragonal CZTSe structure was confirmed. Scanning electron microscopy and energy-dispersive spectroscopy measurements of the morphological and compositional properties indicated large grains and dense surfaces with an elemental composition close to the desired stoichiometry in SLG\SnSe 2 \Cu\ZnSe and SLG\SnSe 2 \Cu 2 Se\ZnSe stacks. To ascertain the surface chemistry and unique characteristics of the produced films, additional X-ray photoemission spectroscopy experiments were carried out. The optimal band gap values for the absorber layers were found using conventional spectroscopy, and they ranged from 0.88 to 1.47 eV. According to the electrical measurements, all the films were p-type and have high carrier concentrations between 1016 and 1020 cm−3. Our findings demonstrate that employing a sequential deposition approach and annealing in different atmospheres can yield CZTSe absorber layers with desirable properties, overcoming the challenge of non-stoichiometric CTSe precursors. [ABSTRACT FROM AUTHOR]

Energy sustainability is critical for social activities in the human world. The quaternary compound Cu2ZnSnSe4 (CZTSe), as a promising candidate for thin-film solar cell absorption with medium-level thermoelectric performance, is of interest for the purpose of utilizing solar energy. The defect chemistry and atomic ordering in this particular compound also triggers interests in understanding its crystallographic structure as well as defects. Hereby, high energy resolution X-ray absorption spectroscopy is employed to investigate the electronic and geometric structural complexity in pristine and cobalt-doped Cu2ZnSnSe4. The occupational atomic sites of Cu are found to be mixed with the Zn atoms, forming CuZn anti-defects, which serve as a knob to tune local electronic structures. With proper doping, the band structure can be manipulated to improve the optical and thermoelectric properties of the CZTSe compounds. [ABSTRACT FROM AUTHOR]

• The investigation of the defect-related carrier dynamics of CZTSe conducted in this study provided the experimental characterization of the existence of [2Cu Zn − + Sn Zn 2+] defect clusters. From the results, it is important to consider the possibility of factors such as the presence of [2Cu Zn − + Sn Zn 2+] defect clusters when determining the source of the performance degradation of CZTSe solar cells. In this work, a systematic investigation of the effects of point defects on the efficiency of a Cu 2 ZnSnSe 4 (CZTSe) thin film solar cell was conducted using temperature-/power-dependent photoluminescence (PL) and time-resolved photo-luminescence (TRPL). The studied stoichiometric CZTSe absorber layer for a CZTSe solar cell with an efficiency of 4.4 % was prepared using the low-toxicity selenization process. The fitting to the Arrhenius plot and the stretched tail at the long-wavelength side of PL spectrum obtained at 10 K indicated a high concentration of zinc on copper (Cu Zn) point defects. The dispersive-photon-energy-dependent TRPL at 10 K exhibited non-exponential stretched PL decay at all photon energies and, in particular, revealed the highly fluctuating potential of CZTSe that caused carrier localization. This effect was observed to be caused by [2Cu Zn − + Sn Zn 2+] defect clusters, which produce a significant conduction/valence band-edge shift in their vicinity in CZTSe and can cause shunt leakage and an increase in series resistance. This systematic investigation presents the experimental characterization of [2Cu Zn − + Sn Zn 2+] defect clusters and provides perspective to help clarify the performance deterioration of CZTSe solar cells. [ABSTRACT FROM AUTHOR]

Copper-based chalcogenides have emerged as promising thermoelectric materials due to their high thermoelectric performance, tunable transport properties, earth abundance and low toxicity. We have presented an overview of experimental results and first-principal calculations investigating the thermoelectric properties of various polymorphs of Cu2SnS3 (CTS), Cu2ZnSnS4 (CZTS), and Cu2ZnSnSe4 (CZTSe) synthesized by high-energy reactive mechanical alloying (ball milling). Of particular interest are the disordered polymorphs of these materials, which exhibit phonon-glass–electron-crystal behavior—a decoupling of electron and phonon transport properties. The interplay of cationic disorder and nanostructuring leads to ultra-low thermal conductivities while enhancing electronic transport. These beneficial transport properties are the consequence of a plethora of features, including trap states, anharmonicity, rattling, and conductive surface states, both topologically trivial and non-trivial. Based on experimental results and computational methods, this report aims to elucidate the details of the electronic and lattice transport properties, thereby confirming that the higher thermoelectric (TE) performance of disordered polymorphs is essentially due to their complex crystallographic structures. In addition, we have presented synchrotron X-ray diffraction (SR-XRD) measurements and ab initio molecular dynamics (AIMD) simulations of the root-mean-square displacement (RMSD) in these materials, confirming anharmonicity and bond inhomogeneity for disordered polymorphs. [ABSTRACT FROM AUTHOR]

In this work, a two-step method for preparation of CZTSe (Cu2ZnSnSe4) single crystals was demonstrated for the first time by recrystallization of a polycrystalline material in a KI-KCl meltsolution in a temperature gradient. At the first step, a polycrystalline material consisting of a mixture of metal selenides was synthesized by direct fusion of elemental Cu, Zn, Sn, and Se at 1000°C. Next, recrystallization process was carried out at a temperature gradient of 100°C, while the temperature of the cold zone was 750°C. The phase and chemical composition of the crystals were studied by energy dispersive X-ray and Raman spectroscopy. It was shown that the charge composition does not affect the composition of the obtained crystals. According to the amount of the remaining charge in the hot zone, one can speak of a very low recrystallization rate and a low product yield. Analysis of the elemental composition of crystals from the cold zone revealed a high inhomogeneity even in one experiment, which indicates the need to optimize the experimental parameters. On the other hand, according to the full line width at half height of the main peak, it can be argued that the obtained samples have a high degree of order in the structure and are suitable for measuring of physical characteristics. [ABSTRACT FROM AUTHOR]

Wet ball milling was used for the synthesis of Cu2ZnSnSe4 (CZTSe) nanoparticles with a kesterite structure. The prepared nanoparticles were used for ink formulation. Surfactants and binders were added to improve the ink stability, prevent agglomeration, and enhance ink adhesion. The films deposited via spin coating were annealed at different temperatures using a rapid thermal processing system in the presence of selenium powder in an inert environment. Analytical techniques, such as X-ray diffraction, Raman spectroscopy, and Fourier-transform infrared spectroscopy, were used to confirm the formation of CZTSe nanoparticles with a single-phase, crystalline kesterite structure. Field-emission scanning electron microscopy and energy-dispersive X-ray spectroscopy were used to study the surface morphology and chemical composition of the thin films before and after annealing, with and without the sodium solution. The optoelectrical properties were investigated using ultraviolet-visible spectroscopy and Hall measurements. All the prepared CZTSe thin films exhibited a p-type nature with an optical bandgap in the range of 0.82–1.02 eV. The open-circuit voltage and fill factor of the CZTSe-based devices increased from 266 to 335 mV and from 37.79% to 44.19%, respectively, indicating a decrease in the number of recombination centers after Na incorporation. [ABSTRACT FROM AUTHOR]

In this work, Cu2ZnSnSe4 nanocrystals were synthesized by the polyol method. The chemical composition and morphological, structural, and microstructural properties of Cu2ZnSnSe4 nanocrystals, depending on the synthesis temperature and time, as well as the composition of the precursor, have been thoroughly investigated using scanning and transmission electron microscopy, energy dispersive X-ray analysis, X-ray diffraction, FTIR spectroscopy, Raman spectrometry, and low-temperature photoluminescence. We compared the properties of nanocrystals synthesized from different precursors containing selenourea or amorphous selenium as a source of selenium and then determined the optimal conditions for the synthesis of nanocrystals. It was found that the optimal synthesis time for nanocrystals obtained in the first approach is τ = 30-45 min, and in the second approach - τ = 120 min. It was also found that the optimal composition for the synthesis of single-phase Cu2ZnSnSe4 nanocrystals in the second approach is the molar ratio of precursors 2:1.5:1:4, and the synthesis temperature T = 280◦C. Thus, Cu2ZnSnSe4 nanocrystals synthesized under optimal conditions are used to develop nanoinks for printing solar cell absorbers by two- and three-dimensional printers. [ABSTRACT FROM AUTHOR]

In recent years, the search for more efficient and environmentally friendly materials to be employed in the next generation of thin film solar cell devices has seen a shift towards hybrid halide perovskites and chalcogenide materials crystallising in the kesterite crystal structure. Prime examples for the latter are Cu 2 ZnSnS 4 , Cu 2 ZnSnSe 4 , and their solid solution Cu 2 ZnSn(S x Se 1 − x ) 4 , where actual devices already demonstrated power conversion efficiencies of about 13 %. However, in their naturally occurring kesterite crystal structure, the so-called Cu-Zn disorder plays an important role and impacts the structural, electronic, and optical properties. To understand the influence of Cu-Zn disorder, we perform first-principles calculations based on density functional theory combined with special quasirandom structures to accurately model the cation disorder. Since the electronic band gaps and derived optical properties are severely underestimated by (semi)local exchange and correlation functionals, supplementary hybrid functional calculations have been performed. Concerning the latter, we additionally employ a recently devised technique to speed up structural relaxations for hybrid functional calculations. Our calculations show that the Cu-Zn disorder leads to a slight increase in the unit cell volume compared to the conventional kesterite structure showing full cation order, and that the band gap gets reduced by about 0.2 eV, which is in very good agreement with earlier experimental and theoretical findings. Our detailed results on structural, electronic, and optical properties will be discussed with respect to available experimental data, and will provide further insights into the atomistic origin of the disorder-induced band gap lowering in these promising kesterite type materials. [ABSTRACT FROM AUTHOR]

Energy sustainability is critical for social activities in the human world. The quaternary compound Cu2ZnSnSe4 (CZTSe), as a promising candidate for thin-film solar cell absorption with medium-level thermoelectric performance, is of interest for the purpose of utilizing solar energy. The defect chemistry and atomic ordering in this particular compound also triggers interests in understanding its crystallographic structure as well as defects. Hereby, high energy resolution X-ray absorption spectroscopy is employed to investigate the electronic and geometric structural complexity in pristine and cobalt-doped Cu2ZnSnSe4. The occupational atomic sites of Cu are found to be mixed with the Zn atoms, forming CuZn anti-defects, which serve as a knob to tune local electronic structures. With proper doping, the band structure can be manipulated to improve the optical and thermoelectric properties of the CZTSe compounds.

Copper-based chalcogenides have emerged as promising thermoelectric materials due to their high thermoelectric performance, tunable transport properties, earth abundance and low toxicity. We have presented an overview of experimental results and first-principal calculations investigating the thermoelectric properties of various polymorphs of Cu2SnS3 (CTS), Cu2ZnSnS4 (CZTS), and Cu2ZnSnSe4 (CZTSe) synthesized by high-energy reactive mechanical alloying (ball milling). Of particular interest are the disordered polymorphs of these materials, which exhibit phonon-glass–electron-crystal behavior—a decoupling of electron and phonon transport properties. The interplay of cationic disorder and nanostructuring leads to ultra-low thermal conductivities while enhancing electronic transport. These beneficial transport properties are the consequence of a plethora of features, including trap states, anharmonicity, rattling, and conductive surface states, both topologically trivial and non-trivial. Based on experimental results and computational methods, this report aims to elucidate the details of the electronic and lattice transport properties, thereby confirming that the higher thermoelectric (TE) performance of disordered polymorphs is essentially due to their complex crystallographic structures. In addition, we have presented synchrotron X-ray diffraction (SR-XRD) measurements and ab initio molecular dynamics (AIMD) simulations of the root-mean-square displacement (RMSD) in these materials, confirming anharmonicity and bond inhomogeneity for disordered polymorphs.

Wet ball milling was used for the synthesis of Cu2ZnSnSe4 (CZTSe) nanoparticles with a kesterite structure. The prepared nanoparticles were used for ink formulation. Surfactants and binders were added to improve the ink stability, prevent agglomeration, and enhance ink adhesion. The films deposited via spin coating were annealed at different temperatures using a rapid thermal processing system in the presence of selenium powder in an inert environment. Analytical techniques, such as X-ray diffraction, Raman spectroscopy, and Fourier-transform infrared spectroscopy, were used to confirm the formation of CZTSe nanoparticles with a single-phase, crystalline kesterite structure. Field-emission scanning electron microscopy and energy-dispersive X-ray spectroscopy were used to study the surface morphology and chemical composition of the thin films before and after annealing, with and without the sodium solution. The optoelectrical properties were investigated using ultraviolet-visible spectroscopy and Hall measurements. All the prepared CZTSe thin films exhibited a p-type nature with an optical bandgap in the range of 0.82–1.02 eV. The open-circuit voltage and fill factor of the CZTSe-based devices increased from 266 to 335 mV and from 37.79% to 44.19%, respectively, indicating a decrease in the number of recombination centers after Na incorporation.

In recent years, the search for more efficient and environmentally friendly materials to be employed in the next generation of thin film solar cell devices has seen a shift towards hybrid halide perovskites and chalcogenide materials crystallising in the kesterite crystal structure. Prime examples for the latter are Cu2ZnSnS4, Cu2ZnSnSe4, and their solid solution Cu2ZnSn(SxSe1−x)4, where actual devices already demonstrated power conversion efficiencies of about 13 %. However, in their naturally occurring kesterite crystal structure, the so-called Cu-Zn disorder plays an important role and impacts the structural, electronic, and optical properties. To understand the influence of Cu-Zn disorder, we perform first-principles calculations based on density functional theory combined with special quasirandom structures to accurately model the cation disorder. Since the electronic band gaps and derived optical properties are severely underestimated by (semi)local exchange and correlation functionals, supplementary hybrid functional calculations have been performed. Concerning the latter, we additionally employ a recently devised technique to speed up structural relaxations for hybrid functional calculations. Our calculations show that the Cu-Zn disorder leads to a slight increase in the unit cell volume compared to the conventional kesterite structure showing full cation order, and that the band gap gets reduced by about 0.2 eV, which is in very good agreement with earlier experimental and theoretical findings. Our detailed results on structural, electronic, and optical properties will be discussed with respect to available experimental data, and will provide further insights into the atomistic origin of the disorder-induced band gap lowering in these promising kesterite type materials.

Summary: 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. [ABSTRACT FROM AUTHOR]

A truly simple, reproducible, and environmentally friendly non‐vacuum synthesis method for synthesising of carbon‐free Cu2ZnSnSe4 (CZTSe) absorber layer has been presented. The stannite CZTSe nanoparticles with an average size of about 20 nm distributions were fabricated by an ambient mechanical milling procedure using Cu2Se, Zn, Sn, elemental selenium powders as raw materials and non‐toxic ethanol as solvent. The compact CZTSe thin films were formed via an annealing treatment under Ar/Se atmosphere using rapid thermal processing. The optical properties of the obtained CZTSe thin films are the absorption coefficient (α) exceeding 104 cm−1 and Eg of 0.91 eV. The electrical properties of the CZTSe thin films indicate p‐type semiconductor behaviour. The photovoltaic properties of this solar cell are power conversion efficiency of 0.18%. [ABSTRACT FROM AUTHOR]

A Cu 2 ZnSnSe 4 (CZTSe) photovoltaic absorber thin films were prepared using a 2-step selenization process on a Ti substrate including a Na precursor layer and a Na-free Ti substrate, and the effect of Na on the solar cell performance was compared. A CZTSe flexible solar cell fabricated on a Ti foil substrate exhibited an efficiency of 3.06%, which was less than half that of a solar cell fabricated on a soda lime glass substrate. This was attributed to the absence of Na and severe Zn crowding near the back contact. By depositing a 100‐nm-thick sodalime glass thin film on a Ti substrate to supply Na, the efficiency increased up to 5.59%. In the Na-doped CZTSe absorber layer grown on the Ti substrate, the back crowding of Zn was eliminated and the upper part of the absorption layer was converted to a Zn-rich environment, which prevented the formation of Cu Zn antisite defects. Image 1 • Cu 2 ZnSnSe 4 solar cells on a flexible Ti foil using a two step process. • By supplying Na using soda-lime thin film, the efficiency of 5.59% was obtained. • Na has a great influence on the local distribution of Cu and Zn and hole concentration. • Depending on the presence of Na, the Cu diffusion and the MoSe 2 thickness varied. [ABSTRACT FROM AUTHOR]

• CZTSe thin films were fabricated by electrodeposited precursors and selenization. • Temperature-dependent Raman spectroscopic study in range 24–290 K was carried out. • Decrease in temperature leads to shifts position and linewidht of Raman peaks. • The four-phonon process is main reason of position and linewidth of Raman peaks variation. • Possible dependence of the temperature/anharmonic constants on composition of CZTSe was discussed. The temperature dependence (in range from 24 to 290 K) of Raman spectroscopy of the Cu 2 ZnSnSe 4 (CZTSe) films with Zn-rich (series A) and Zn-poor (series B) composition obtained on a Ta foil is investigated. Analisys and approximation by the Lorentz function of the CZTSe Raman spectra suggests that the CZTSe most intense Raman peak consists of two modes (at 192/189 and 194/195 cm−1), which are slightly shifted from each other. In addition, the Raman peaks around 192 and 189 cm−1 lead to asymmetric broadening of dominant peaks at 194 and 195 cm−1 in Raman spectra of the CZTSe films series A and B , respectively. In the case of the Sn-rich CZTSe films, we attribute of Raman peak around 189 cm−1 to SnSe 2 compound. However in the case of the Sn-poor CZTSe films, the observable shift is too high to assign confidently the 192 cm−1 band to a SnSe 2 compound, which was not detected by XRD analysis. We suppose that this mode is attributed to disordered kesterite structure. The temperature dependence Raman spectra for both series of the CZTSe films shows that a change temperature from 290 to 24 K leads to position shift and narrowing of the CZTSe Raman A-modes. The calculated temperature coefficients and anharmonic constants in Klemens model approximations for temperature dependence of shift position and FWHM of the CZTSe A-modes shown that four-phonon process has dominant contribution in damping process and as a consequence in Raman spectrum changes for two series of the CZTSe films. [ABSTRACT FROM AUTHOR]

This study analyzes the electronic structure of Cu2ZnSn1–xGexSe4 (CZTGSe) surface and band alignments of CdS and CZTGSe using the Ge/(Sn + Ge) composition ratios of x = 0–1 based on inversed, ultraviolet, and X‐ray photoemission spectroscopy. The conduction band offsets of the CdS/CZTGSe interface linearly decrease with increasing x, which are so‐called spike conduction band connections, whereas the valence band offsets are observed to be independent of x. Moreover, the hole density near the CZTGSe surface increases with an increase in x; this corresponds to the increase in the measured built‐in‐potential with x. However, the open circuit voltage (VOC) saturates to ≈0.5 V for x over 0.2 in spite of the favorable band alignment and larger built‐in‐potential of x at the interface. External‐quantum‐efficiency spectral analysis shows that the carrier recombination in CZTGSe bulk is suppressed with an increase in x, whereas the recombination near the CZTGSe surface is enhanced. The relationship between these recombination centers, electronic structure, and saturation of VOC is discussed. [ABSTRACT FROM AUTHOR]

In this paper, Cu2ZnSnSe4 (CZTSe) thin films were prepared by thermal evaporation method and annealed at 300°C for three different annealing time (2, 4, and 6 h) in air atmosphere. The XRD studies indicates that the as deposited films shows amorphous nature and annealed films confirms the formation of CZTSe compound and its average crystallite size increase with increase in annealing time. Among the films, the 2 h annealed film shows higher crystallinity. AFM images show bigger size particels for annealed films. DRS spectra of all the films show good optical absorption in the entire visible range and the band gap is found in the range of 1.45–1. 54 eV. Therefore the annealed films show good photosensing behavior. [ABSTRACT FROM AUTHOR]

Cu2ZnSnSe4 (CZTSe) thin film has been synthesized onto silicon substrates by liquid phase epitaxial growth for the first time in which Au/CZTSe/n-Si/Al heterojunction was successfully fabricated by this technique. The crystal structure and morphology of the CZTSe film were characterized by field emission scanning electron microscopy (FE-SEM) and X-ray diffraction (XRD). The I-V characteristics of the CZTSe/n-Si heterojunction in the dark have been studied at different temperatures ranged from 298 to 398 K to determine the diode parameters such as the rectification ratio, series and shunt resistances (RR, Rs and Rsh resp.), the effective barrier height (ϕb) and the diode ideality factor (n). The CZTSe/n-Si heterojunction shows an excellent rectification behavior. The ideality factor n, series resistance RS, and shunt resistance RSh, were decreased with increasing the temperature. The photovoltaic constants such as VOC, JSC, fill factor and the efficiency of CZTSe/n-Si heterojunction have been calculated from the I-V characteristics under illumination. The CZTSe/n-Si heterojunction exhibits efficiency about 3.42% at room temperature. The dielectric measurements proved that the CZTSe/n-Si heterojunction device shows the behavior of two forward biased Schottky diodes. [ABSTRACT FROM AUTHOR]

Nowadays, most of the best efficiencies of Cu2ZnSn(S,Se)4 (CZTSSe) solar cells are obtained from absorber layers fabricated using sequential processes, including the deposition of metallic stack precursors, typically by sputtering, and followed by reactive annealing under chalcogen atmosphere. The sputtering technique is widely known for the easy growth of metallic layers, although the deposition rates, growth morphology and nucleation, or the roughness can sometimes be an issue leading to inhomogeneities in the final layers. Nevertheless, MBE (molecular beam epitaxy) technique could have some advantages to obtain high‐quality metallic layers, with accurate control of the growth due to ultra‐high vacuum conditions and high purity. In this work, we study the use of advanced MBE systems to grow metallic stack precursors, alternatively to sputtering or thermal evaporation techniques, to obtain high‐quality CZTSe:Ge absorbers. Due to differences in the nature of each type of precursor, thermal annealing optimizations are presented by modifying some critical selenization parameters, such as the temperature or the selenium amount in order to obtain well‐crystallized absorbers. Detailed morphological, compositional, and structural characterizations show relevant features of each precursor, mainly related to the formation of MoSe2 at the back interface, and Se and Sn composition after selenization in different conditions. Regarding the solar cell devices, main efficiency limitations come from VOC and FF, which could be tentatively related to a noncontrolled selenization; different precursor reactivity, porosity, or composition; and different alkali diffusion during the reactive annealing. Finally, in the first optimization, a 9.2% efficiency device has been achieved with promising perspectives for future improvements. [ABSTRACT FROM AUTHOR]

Spectroscopic ellipsometry is applied to investigate the effect of Cu/Zn disorder in a Cu 2 ZnSnSe 4 crystal on the optical transitions. We observe that the degree of order has an impact not only on the first optical transition E 0 at the gamma point, which is the commonly discussed direct band gap in kesterites. It also varies the further optical transition E 1 away from the gamma point. While E 0 shows an increasing trend with higher degree of order, the transition E 1 shows an opposite behavior, indicating a fundamental impact of disorder on the shape of the electronic bands of kesterite material. • SE was used to investigate the effect of different degrees of Cu-Zn order in Cu 2 ZnSnSe 4 crystal on the optical transitions. • Cu/Zn ordering not only effects the fundamental band gap E 0 , it also effects the further optical transition E 1. • While E 0 is increasing with increasing Cu/Zn ordering level in Cu 2 ZnSnSe 4 crystal, E 1 shows an opposite behavior. • Relative energy differences between ordered and disordered state in this study are in good agreement with previous reports. [ABSTRACT FROM AUTHOR]

Abstract Cu-Zn-Sn-S sulfide precursors with various thicknesses, ranging from 0.8 µm to 1.7 µm were annealed under two types of annealing atmosphere: a pure (Se) atmosphere and a mix of (S+Se) one. Pure (Se) annealing led to the Cu 2 ZnSn(S,Se) 4 (CZTSSe) phase with a Se gradient from front to back surface. Annealing under mixture of (S+Se) improved the homogeneity of the CZTSSe solid solution across the whole layer thickness and prevented the S loss from sulfide precursor. This increased the band gap of the absorber, but enhanced the occurrence of S-rich secondary phases, mainly ZnS thin layers formed at the Mo/CZTSSe interface. The decrease of the absorber thickness can limit the occurrence of secondary phases and affects electrical parameters of the solar cells. While the best cell efficiency of 7.1% was obtained for a 1.7 µm-thick layer annealed under pure Se atmosphere, the best and homogeneous average efficiencies on 2.5 × 2.5 cm2 samples were obtained for a 0.8 µm-thick layer annealed under (S+Se) atmosphere. These results showed clearly the trade-off to find between the annealing atmosphere and the thickness of the absorber. Highlights • Pure (Se) annealing leads to the Se graded CZTSSe phase. • (S+Se) annealing favors the homogeneity of CZTSSe and prevents the S loss from sulfide precursor. • Electric properties of the solar cells depends on the Se or (S+Se) annealing atmosphere. • High thickness causes the formation of ZnS and Sn(S,Se) secondary phases. [ABSTRACT FROM AUTHOR]

Abstract Cu 2 ZnSnSe 4 (CZTSe) and Ag 2 ZnSnSe 4 (AZTSe) thin films were deposited on FTO substrates by the thermal evaporation method and the films were annealed at 300 °C for 2 h. The XRD analysis confirms the formation of tetragonal structure for both CZTSe and AZTSe thin films. The introduction of Ag instead of Cu is confirmed by the major crystalline peak (112) shift towards lower angle 2θ = 26.1° (for AZTSe). In the Raman spectra, the noticeable vibrations appeared at 186 cm−1 and 183 cm−1 confirm the formation of CZTSe and AZTSe thin films. Raman technique also found the presence of SnSe as a secondary phase. By comparing the optical spectra, the AZTSe film has higher absorption in the visible region than the CZTSe thin films which is attributed to the surface plasmon resonance of Ag. AFM images show a pyramidal structure for both CZTSe and AZTSe films. The Mott-Schottky plot shows p-type conductivity for FTO/CZTSe while there is n-type conductivity for a FTO/AZTSe thin film. The variation in the conductivity is due to replacing Cu with Ag. Photoelectrochemical cell (PEC) performance was employed in the presence of a polysulfide electrode by a standard three-electrode system. By comparing the value of V oc , the AZTSe film shows higher V oc than CZTSe films which is important for photovoltaic applications. The Photoconversion efficiency (PCE) is measured to be 0.31% for FTO/AZTSe thin films, while it is low about 0.29% for FTO/CZTSe. The impedance plot shows the semicircular nature for both the FTO/CZTSe and FTO/AZTSe films. Graphical abstract Image 1 Highlights • Cu 2 ZnSnSe 4 (CZTSe) and Ag 2 ZnSnSe 4 (AZTSe) thin films prepared of FTO substrates. • XRD and Raman analysis confirms the formation of tetragonal structured CZTSe and AZTSe thin films. • The Mott-schottky plot shows p-type for FTO/CZTSe and n-type conductivity for FTO/AZTSe thin film. • FTO/AZTSe shows higher Voc and higher efficiency. [ABSTRACT FROM AUTHOR]

The chemical reactions between CuSe, SnSe and ZnSe and their enthalpies in molten CdI2 in closed vacuum ampoules were investigated. Differential thermal analysis (DTA) was used for the determination of the temperatures of processes occurring in the studied mixtures. X-ray diffraction and Raman spectroscopy were performed to discover the phase changes in the long-term annealed samples at higher than peak temperatures in DTA. The occurring chemical reactions and their enthalpies were derived. The recrystallization of CZTSe in CdI2 was investigated. The results confirmed the formation of Cu2SnSe3, Cu2SnSe4, CdSe, Cu2CdSnSe4, Cu2ZnSnSe4, and Zn1−xCdxSe compounds and solid solutions. [ABSTRACT FROM AUTHOR]

The chemical reactions between CuSe, SnSe and ZnSe and their enthalpies in molten CdI2 in closed vacuum ampoules were investigated. Differential thermal analysis (DTA) was used for the determination of the temperatures of processes occurring in the studied mixtures. X-ray diffraction and Raman spectroscopy were performed to discover the phase changes in the long-term annealed samples at higher than peak temperatures in DTA. The occurring chemical reactions and their enthalpies were derived. The recrystallization of CZTSe in CdI2 was investigated. The results confirmed the formation of Cu2SnSe3, Cu2SnSe4, CdSe, Cu2CdSnSe4, Cu2ZnSnSe4, and Zn1−xCdxSe compounds and solid solutions. [ABSTRACT FROM AUTHOR]

Cu2ZnSnSe4 (CZTSe) polycrystalline thin films have been prepared on molybdenum coated soda-lime glass substrates by DC magnetron sputtering technique. Two different deposition orders for the metallic precursors were tested, namely Mo/Cu/Zn/Sn and Mo/Zn/Cu/Sn. The influence of the precursor's deposition order on the structural and optical parameters of the obtained thin films was studied. Structural analyses were done based on the results of XRD and stylus profilometry measurements. Optical transmittance measurements were performed in order to estimate the band gap energy of the CZTSe films. All XRD spectra show preferred growth orientation along (112) crystallographic plane. The average size of the grains calculated from XRD data is slightly bigger for the Mo/Zn/Sn/Cu sequence. The profilometry analysis shows that the average roughness and thickness of the layer were also bigger for that deposition order. Optical band gap energies derived from transmittance measurements were 1.23eV and 1.27eV for Mo/Cu/Zn/Sn and Mo/Zn/Cu/Sn, respectively. [ABSTRACT FROM AUTHOR]

The photoluminescence (PL) spectra of Cu 2 ZnSnSe 4 microcrystals with two different degrees of disorder were investigated by measuring the dependencies on the temperature and excitation power. Crystals were cooled at different rates after the high-temperature annealing treatment in order to change the degree of disorder. The PL spectra of both samples consist of one asymmetrical band located at 0.88 and 0.92 eV for disordered and ordered crystals, respectively. At low temperatures, both samples have similar origins of PL involving localized electron states. In the case of the ordered sample, we observed deeper localized electron states, thus higher temperatures were needed to empty the electrons from these states to the band states. Changes in the degree of disorder lead to changes in the radiative recombination in CZTSe microcrystals. • Photoluminescence study of CZTSe microcrystals with different degrees of disorder is presented. • The emission bands were located at 0.88 and 0.92 eV at T = 10 K for disordered and ordered samples, respectively. • Localized electron states were detected in both samples, being deeper in the ordered CZTSe. • The PL bands were attributed to TI and BI transitions coexisting at low temperatures. [ABSTRACT FROM AUTHOR]

This study reports on substantial improvement of the open-circuit voltage ( Voc) of Cu2ZnSnSe4 (CZTSe) thin film solar cells by applying a passivation strategy to both the top and bottom interfaces of the CZTSe absorber, which involves insertion of a thin dielectric layer between the CZTSe and the surrounding layers. The study also presents in-depth material characterizations using transmission electron microscopy, energy dispersive X-ray spectroscopy, low-temperature photoluminescence, and secondary ion mass spectrometry, to reveal the effects of the interface passivation. To passivate the bottom Mo/CZTSe interface, a dielectric layer with patterned local contacts of dimensions down to ~100 nm was prepared using nanosphere lithography. With this, the Voc, short-circuit current, and fill factor (FF) were significantly enhanced due to reduction in carrier recombination at the bottom Mo/CZTSe interface. The top CZTSe/CdS interface was passivated by a thin dielectric layer which prevented inter-diffusion of Cd and Cu at the top interface, thereby improving the junction quality. Application of the top passivation layers resulted in substantial improvement in Voc and FF, thereby achieving the Voc deficit of 0.542 V which is the record value among reported CZTSe solar cells. Copyright © 2017 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Cu 2 ZnSnSe 4 (CZTSe) films with different Zn/Sn ratios were fabricated using Cu 2 SnSe 3 (CTSe) and ZnSe bilayer precursors (ZnSe/CTSe/Mo) and sandwich-structured precursors (ZnSe/CTSe/ZnSe/Mo). Using the bilayer precursor, excessive ZnSe on top of the CZTSe films with a Zn/Sn ratio of 1.3 that acts as a current-blocking barrier was observed, reducing the short-circuit current density of the CZTSe solar cells. Modification of the precursor structure from the bilayer to the sandwiched structure eliminates the segregation of ZnSe phase on top of the film even for a high (1.25) Zn/Sn ratio. This modification improved the cell efficiency from 6% (bilayer precursor) to 9% (sandwich-structured precursor). [ABSTRACT FROM AUTHOR]

In this study, an ultra-thin MoO3 layer synthesized by a solution-based technique is introduced as a promising interfacial layer to improve the performance of kesterite Cu2ZnSnSe4 (CZTSe) solar cell. Solar cells with 10 nm of MoO3 between Mo rear contact and CZTSe had larger minority carrier life time and open-circuit voltage compared to the reference solar cells. Temperature dependent current density-voltage measurement indicated that the activation energy ( EA) of the main recombination is higher (∼ 837 meV) in solar cells with MoO3 layer, as compared to conventional solar cells where EA ∼ 770 meV, indicating reduced interface recombination. A best efficiency of 7.1% was achieved for a SLG/Mo/MoO3/CZTSe/CdS/TCO solar cell compared to the reference solar cell SLG/Mo/CZTSe/CdS/TCO for which 5.9% efficiency was achieved. [ABSTRACT FROM AUTHOR]

The standard enthalpy of formation of the Cu2ZnSnSe4 compound has been determined by measuring the heat of its formation from its constituent elements according to the reaction scheme 2Cu + Zn + Sn + 4Se → Cu2ZnSnSe4 in a calorimeter: (Cu2ZnSnSe4) = –392.00 ± 2.56 kJ/mol. [ABSTRACT FROM AUTHOR]

Low-temperature cation ordering is emerging as a critical factor limiting the efficiency of CZTSSe kesterite photovoltaic materials. By means of direct determination of the site occupancies from anomalous X-ray powder diffraction data at the Cu- and Zn-absorption edges, the ordering of Cu+ and Zn2+ in B-type Cu2ZnSnSe4 (CZTSe) kesterite upon annealing at temperatures below 203 (6) °C is demonstrated. Anomalous X-ray diffraction on the Cu- and Zn-K absorption edges allows determination of the distribution of isoelectric Cu1+ and Zn2+ over the crystallographic sites in a B-type CZTSe kesterite (Cu1.949(20)Zn1.059(10)Sn0.983(10)Se4) powder. By Rietveld refinement the quantitative determination of both Cu- and Zn-occupancy for all relevant sites is achieved. From this, the temperature dependency of a structure-based, quantitative order parameter is determined. The critical temperature of the phase transition is confirmed at 203 (6) °C. The ordering mechanism is in agreement with a transition from disordered to ordered kesterite. The photoluminescence band maximum shows a closely related temperature dependency, directly demonstrating the effect of cation ordering on the optical properties of CZTSe. [ABSTRACT FROM AUTHOR]

In our recently published work, the positive effect of a Ge nanolayer introduced into the processing of Cu2ZnSnSe4 absorbers (CZTSe) was demonstrated. In this contribution, the complete optimization of this new approach is presented for the first time. Hence, the optimum Ge nanolayer thickness range is defined in order to achieve an improved performance of the devices, obtaining a record efficiency of 10.6%. By employing this optimized approach, the open-circuit voltage ( VOC) is boosted for our pure selenide CZTSe up to 489 mV, leading to VOC deficit among the lowest reported so far in kesterite technology. Additionally, two important effects related to the Ge are unambiguously demonstrated that might be the origin of the VOC boost: the improvement of the grain size and the corresponding crystalline quality, and the interaction between Ge and Na that allows for dynamic control over the CZTSe doping. Finally, evidences pointing to the origin of the deterioration of devices properties for large Ge concentrations are presented. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

We obtained Raman spectra of a co-evaporated Cu2ZnSnSe4 (CZTSe) thin film under pressures of up to 5.56 GPa using a gasketed diamond anvil cell. Each spectrum was carefully resolved into Lorentzian peaks to analyze the observed phonons. Six Raman peaks were observed at 1 atm. These Raman peaks appeared at 174, 193, 196, 220, 234, and 248 cm−1 and were attributed to the vibration modes of kesterite CZTSe with B (or A), E, A, E, B, and B symmetries, respectively. Also, two Raman modes with a frequency of approximately 260 cm−1 emerged at 1.27 GPa. A small additional peak with a 220 cm−1 Raman shift was visible at pressures higher than 3.55 GPa. The origins of these peaks are also discussed. [ABSTRACT FROM AUTHOR]

Cu2ZnSnSe4 (CZTSe) solar cell with a facile superstrate structure of carbon/CZTSe/CdS/ITO was fabricated entirely by non-vacuum processes. The influence of selenization temperature on the composition of CZTSe layer was briefly investigated. Compared with current superstrate-type CZTS(e) solar cells, the present CZTSe superstrate solar cell exhibited a higher power conversion efficiency of 2.44%. [ABSTRACT FROM AUTHOR]

[Display omitted] Low-temperature XRD measurements were performed to confirm the phase composition and structural parameters of the electrochemically deposited Cu 2 ZnSnSe 4 thin films on flexible metal substrates. [ABSTRACT FROM AUTHOR]

A large improvement in Cu2ZnSnSe4 solar cell efficiency is presented based on the introduction of a Ge superficial nanolayer. This improvement is explained by three complementary effects: the formation of a liquid Ge‐related phase, the possible reduction of Sn multicharge states, and the formation of GeOx nanoinclusions, which lead to an impressive solar cell (VOC) increase. [ABSTRACT FROM AUTHOR]

Cu2ZnSnSe4 (CZTSe) thin film solar cells are promising emergent photovoltaic technologies based on low-bandgap absorber layer with high absorption coefficient. To reduce optical losses in such devices and thus improve their efficiency, numerical simulations of CZTSe solar cells optical characteristics can be performed based on individual optical properties of each layer present in the cell structure. In this contribution, we have first determined the optical coefficients of individual thin films (i.e., ( n, k) of the absorber, buffer, and window layers) to build a realistic model simulating the optical behavior of the whole cell stack we propose. Optical characterization was performed using two approaches, one based on ellipsometry measurements for characterizing thin flat cadmium sulfide (CdS) and zinc oxide (ZnO) layers and the other relying on reflectance and transmission ( R/ T) analysis for the rough CZTSe absorber. Then, we performed numerical simulations using as input experimental optical parameters predicting optimal CZTSe cell structure minimizing optical losses. The impact of each layer's thickness on the cell's short-circuit current has been studied. A set of optimal thicknesses of each of the active layers was proposed. Finally, the proposed optical optimization was experimented practically leading to CZTSe cells with 9.7% and 10.4% efficiencies. [ABSTRACT FROM AUTHOR]

This paper reports on the reaction mechanism of Cu2ZnSnSe4 (CZTSe) nanoink via a solvent-thermal reflux method using copper (Cu), zinc (Zn), tin (Sn), and selenium (Se) powders as precursors and polyetheramine as a reaction solvent. The formation of CZTSe nanoparticles in polyetheramine began with the formation of binary phase CuSe2 due to the strong catalysis provided by polyetheramine. This was followed by the formation of binary phase ZnSe crystals. In the final stage, ternary crystals of Cu2SnSe3 transformed into well-dispersed nanocrystals of Cu2ZnSnSe4, which are derived from the characterization of XRD, Raman, and TEM. The size of the crystals was shown to decrease with reaction time due to the emulsification effect of the polyetheramine epoxy group. Quaternary phase CZTSe first appeared at 20 h, and then the composition of the CZTSe tended to become Cu-poor and Zn-rich over time. The proposed reaction mechanism of CZTSe nanoparticles in polyetheramine presented a distinct phase transformation and suitable time-composition properties, which benefited to further solution-based solar cell application. [ABSTRACT FROM PUBLISHER]

Cu2ZnSnSe4 ingot was synthesized and then used it and Na2Se powder as evaporation materials to prepare a precursor for selenization process in order to fabricate Cu2ZnSnSe4 thin films for solar cell applications. From EPMA analysis, the Sn content in the thin films was approximately constant with increasing Sn mole ratio and the Se content was under 50 at.% in the first experiment. The Se content in the thin films increased to around 50 at.% by the addition of Se layer in second experiment. XRD study showed that the thin films had a kesterite phase in Cu2ZnSnSe4. The Se layer addition enhanced to grow thin films having a close-packed structure and columnar grains. Cu2ZnSnSe4 thin film solar cells demonstrated Voc= 282 mV, Isc= 3.00 mA/cm2. (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

The substitution energies and migration energies of the alkali-metals of Li, Na, and K atoms in Cu2ZnSnS4 (CZTS) and Cu2ZnSnSe4 (CZTSe) were investigated by first-principles calculations. The migration energies of Li, Na, and K atoms in CZTS and CZTSe are obtained by a combination of linear and quadratic synchronous transit (LST/QST) methods and a nudged elastic band (NEB) method. For CZTS and CZTSe, the substitution energies of NaCu and NaZn are much smaller than that of NaSn. The substitution energy of NaZn is comparable to that of NaCu, indicating that NaCu and NaZn are easily formed in CZTS and CZTSe. The substitution energies of the LiCu and LiZn atoms are smaller than those of NaCu and NaZn, while substitution energies of KCu and KZn atoms are much larger than those of NaCu and NaZn. Therefore, it is difficult to form KCu and KZnin CZTS and CZTSe. The theoretical migration energies of Na atom at Cu site to the nearest Cu vacancy (NaCu→VCu) and Na atom at Zn site to the nearest Cu vacancy (NaZn→VCu) are much smaller than those of (NaSn→VCu). The migration energies of (NaCu→VCu) and (NaZn→VCu) in CZTS and CZTSe are comparable to that of Na atom at Cu site to Cu vacancy (NaCu→VCu) in CIS. The mechanism for the alkali-metal effect of Li, Na, and K in the Cu2ZnSn(S,Se)4 films during the post-deposition treatment of LiF, NaF, and KF is discussed on the basis of the calculated substitution and migration energies. (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

(Cu1-xAgx)2ZnSnS4 (CAZTS) and (Cu1-xAgx)2ZnSnSe4 (CAZTSe) solid solutions with 0 ≤ x ≤ 1.0 were synthesized. Their crystal structures were analyzed by Rietveld refinement of X-ray diffraction data. The refined lattice constants a of the kesterite-type CAZTS and CAZTSe increase with Ag content (x) increasing, while their lattice constants c slightly decrease. Therefore, by increasing x, the c / a ratio decreases from 2 for Cu-based compounds to a value lower than 1.9 for Ag-based compounds. The band-gap energies ( Eg) of CAZTS and CAZTSe solid solutions were determined by their diffuse reflectance spectra. The reflectance edges of the CAZTS and CAZTSe shifted to the longer wavelength side with Ag content increasing at 0.0 ≤ x ≤ 0.2, while they shifted to the shorter wavelength side at 0.2 ≤ x ≤ 1.0. By increasing x, the Eg of CAZTS decreases from 1.49 eV (x=0.0) to 1.47 (x=0.2) and then increases to 2.01 eV (x=1.0); and the Eg of CAZTSe decreases from 0.98 eV (x=0.0) to 0.95 (x=0.2) and then increases to 1.34 eV (x=1.0). There is small bowing in the band gaps of the CAZTS and CAZTSe systems. (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

The substitution energies and migration energies of the alkali-metals of Li, Na, and K atoms in Cu2ZnSnS4 (CZTS) and Cu2ZnSnSe4 (CZTSe) were investigated by first-principles calculations. The migration energies of Li, Na, and K atoms in CZTS and CZTSe are obtained by a combination of linear and quadratic synchronous transit (LST/QST) methods and a nudged elastic band (NEB) method. For CZTS and CZTSe, the substitution energies of NaCu and NaZn are much smaller than that of NaSn. The substitution energy of NaZn is comparable to that of NaCu, indicating that NaCu and NaZn are easily formed in CZTS and CZTSe. The substitution energies of the LiCu and LiZn atoms are smaller than those of NaCu and NaZn, while substitution energies of KCu and KZn atoms are much larger than those of NaCu and NaZn. Therefore, it is difficult to form KCu and KZnin CZTS and CZTSe. The theoretical migration energies of Na atom at Cu site to the nearest Cu vacancy (NaCu→VCu) and Na atom at Zn site to the nearest Cu vacancy (NaZn→VCu) are much smaller than those of (NaSn→VCu). The migration energies of (NaCu→VCu) and (NaZn→VCu) in CZTS and CZTSe are comparable to that of Na atom at Cu site to Cu vacancy (NaCu→VCu) in CIS. The mechanism for the alkali-metal effect of Li, Na, and K in the Cu2ZnSn(S,Se)4 films during the post-deposition treatment of LiF, NaF, and KF is discussed on the basis of the calculated substitution and migration energies. (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

Multi-stage co-evaporation processes for the growth of Cu2ZnSnSe4 (CZTSe) thin films are investigated with time-resolved in situ angle-dispersive X-ray diffraction ( in situ XRD). Different preparation protocols were applied and controlled by in situ laser light scattering ( in situ LLS). The composition of the deposited layers was adjusted by making use of a stoichiometric transitions in the LLS signal at the point where the Cu content equals the [Zn + Sn]. The ability of in situ XRD to distinguish between CZTSe and ZnSe is used to develop new processes that minimize the formation of ZnSe as a secondary phase. At high temperatures, an initially grown ZnSe layer forms at the Mo interface, which may not be incorporated into the CZTSe due to Zn-rich preparation conditions. By using lower temperatures at the beginning, CZTSe growth starts directly and a heating step restores the high temperature of the substrate. Thus, the formation of secondary phases is diminished without losing the benefits of higher preparation temperature. The ZnSe growth is reduced and the formation of a continuous layer is not observed. [ABSTRACT FROM AUTHOR]