Influence of anionic substitution on the electrolyte electroreflectance study of band edge transitions in single crystal Cu< sub> 2 ZnSn (S< i> x Se< sub> 1−< … (original) (raw)
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Composition Dependent Band Gaps of Single Crystal Cu2ZnSn (SxSe1-x) 4 Solid Solutions
Solid State Phenomena, 2013
Single crystals of Cu 2 ZnSn(S x Se 1-x ) 4 (CZTSSe) solid solutions have deen grown by chemical vapor transport technique using ICl 3 as a transport agent. Analyzing the X-ray diffraction patterns reveal that the as-grown CZTSSe solid solutions are crystallized in kesterite structure and the lattice parameters are determined. The S contents of the obtained crystals are estimated by Vegard's law. The composition dependent band gaps of CZTSSe solid solutions are studied by electrolyte electroreflectance (EER) techniques. The band gaps of CZTSSe are evaluated by a lineshape fit of the EER spectra and are found to increase almost linearly with the increase of S content.
Journal of Alloys and Compounds, 2013
Cu-deficient Cu 2 ZnSn(S x Se 1Àx) 4 (CZTSSe) pellets were fabricated by reactive liquid-phase sintering at 600°C with two types of sintering aids of Sb 2 S 3 and Te and two types of compensation discs of CuSe 2 and SnSe 2 for selenization and CuS and SnSe 2 for sulfo-selenization and sulfurization. Selenides of Cu 2 Se, ZnSe, SnSe 2 , and SnSe and sulfides of CuS, ZnS, and SnS were the constituent powders. Comprehensive characterizations of the CZTSSe pellets at different S/(S + Se) ratios were performed. The compositions of Cu, Zn, Sn, and the sum of all anionic elements did not change with the sulfur content. No second phases were detected. The highest mobility of 3.5 cm 2 V À1 s À1 was obtained for CZTSSe at x = 0.5. Electrical property of polycrystalline CZTSSe is important for making thin-film solar cells, but systematic investigation was limited. We systematically measured the electrical property of CZTSSe bulks and found that carrier mobility was an important factor in selecting the absorber materials.
Journal of Materials Research and Technology, 2021
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Journal of Alloys and Compounds, 2011
Polarization-dependent electrolyte electroreflectance (EER) measurements were carried out on the oriented Cu 2 ZnSiS 4 and Cu 2 ZnSiSe 4 single crystals at room temperature. Thin blade single crystals of Cu 2 ZnSiS 4 and Cu 2 ZnSiSe 4 were grown by chemical vapor transport technique using iodine as a transport agent. Laue pattern normal to the basal plane of the as-grown crystal revealed the formation of orthorhombic structure with the normal along [2 1 0] and the c axis parallel to the long edge of the crystal platelet. The polarized EER spectra in the vicinity of the direct band edge of Cu 2 ZnSiS 4 displayed distinct structures associated with transitions from two upper-most valence bands to the conduction band minimum at point. In the E⊥c configuration, the feature designated as E A ∼ 3.345 eV was detected and for E c, only E B ∼ 3.432 eV appeared. For Cu 2 ZnSiSe 4 , three features denoted as E A , E B , and E C at around 2.348, 2.406 and 2.605 eV, respectively, were recorded for E⊥c polarization, whereas in the E c, only E B and E C were the allowed transitions. Based on the experimental observations and a recent band-structure calculation by Chen et al. [Phys. Rev. B 82 (2010) 195203], plausible band structures near the direct band edge of Cu 2 ZnSiS 4 and Cu 2 ZnSiSe 4 have been proposed.
Materials for third generation solar cells and other energy related applications
The primary goal of kesterite alloying is to allow for fine tweaking of the material's characteristics for advanced device engineering. Additionally, it is seen as a viable solution to inherent kesterite absorber difficulties such as the Cu/Zn disorder or Sn multivalency. The most interesting alloying elements for kesterite are Ag replacing Cu, Cd replacing Zn, and Ge replacing Sn for cationic substitution, as well as Se replacing S for anionic substitution. This research work investigates the effect of alloying CZTS with Silver (Ag) (Cation) and Selenium (Se) (Anion) theoretically using Density Functional Theory (DFT). The compounds were found to exhibit indirect bandgap characteristics, with conduction band minima (CBM) and valence band maxima (VBM) located between the N and gamma points of the Brillouin zone for pure kesterite Cu2ZnSnS4 and between the N and A points for alloyed Ag2ZnSnSe4 respectively. The bandgap of around 1.22 eV and 0.78 eV were recorded for the pure and ...
Journal of Alloys and Compounds, 2011
Polarization-dependent electrolyte electroreflectance (EER) measurements were carried out on the oriented Cu2ZnSiS4 and Cu2ZnSiSe4 single crystals at room temperature. Thin blade single crystals of Cu2ZnSiS4 and Cu2ZnSiSe4 were grown by chemical vapor transport technique using iodine as a transport agent. Laue pattern normal to the basal plane of the as-grown crystal revealed the formation of orthorhombic structure with the normal along [2 1 0] and the c axis parallel to the long edge of the crystal platelet. The polarized EER spectra in the vicinity of the direct band edge of Cu2ZnSiS4 displayed distinct structures associated with transitions from two upper-most valence bands to the conduction band minimum at Γ point. In the E⊥c configuration, the feature designated as EA ∼ 3.345 eV was detected and for Е‖c, only EB ∼ 3.432 eV appeared. For Cu2ZnSiSe4, three features denoted as EA, EB, and EC at around 2.348, 2.406 and 2.605 eV, respectively, were recorded for E⊥c polarization, whereas in the Е‖c, only EB and EC were the allowed transitions. Based on the experimental observations and a recent band-structure calculation by Chen et al. [Phys. Rev. B 82 (2010) 195203], plausible band structures near the direct band edge of Cu2ZnSiS4 and Cu2ZnSiSe4 have been proposed.► Electrolyte electroreflectance study of Cu2ZnSiS(Se)4 were performed at 300 K. ► Cu2ZnSiS4 exhibits EA and EB anisotropic excitonic transitions for E⊥c and Е‖c. ► Cu2ZnSiSe4 shows EA, EB, and EC for E⊥c, whereas in the Е‖c, only EB and EC appear. ► A plausible band structure near the direct band edge of Cu2ZnSiS(Se)4 is proposed.
Optical Materials, 2018
In this paper, kesterite films have been prepared by sulfurization of co-electrodeposited CueZneSn (CZT) precursor using Na 2 SO 4 as a complexing agent. The structural, morphological, optical and electrical properties of the films have been investigated in details. Adherent layers and pure kesterite phase were obtained. XRD analysis revealed the formation of a tetragonal crystal structure CZTS phase with majors and intense peaks (112), (200), (220), (312) plans. Raman analysis, using different wavelengths laser, confirmed the presence of a pure kesterite phase with minor trace of secondary phases in depth layer. SEM analyses show uniform and compact surface morphology with well definite boundary submicron particles. The absorption coefficient is higher than 1 Â 10 4 cm À1 in the visible region. Electrical measurements, performed in the temperature range of 300 K-100 K, confirmed the p-type conductivity with high free carrier concentrations. For temperatures higher than 200 K, the conductivity is ensured by the emission of free carriers above the potential barriers at the grain boundaries with activation energy close to 51 meV. For temperatures between 200 and 160 K, conduction is provided by nearest neighboring jumps (NNH) mechanism.
Semiconductor Cu 2 ZnSn(S x Se 1−x) 4 (CZTSSe) solid solution is considered as a perspective absorber material for solar cells. However, during its synthesis or deposition, any modification in the resulting optical properties is hardly predicted. In this study, experimental and theoretical analyses of CZTSSe bulk crystals and thin films are presented based on Raman scattering and absorption spectroscopies together with compositional and morphological characterizations. CZTSSe bulk and thin films are studied upon a change in the x = S/(S + Se) aspect ratio. The morphological study is focused on surface visualization of the solid solutions, depending on x variation. It has been discovered for the first time that the surface of the bulk CZTSSe crystal with x = 0.35 has pyramid-like structures. The information obtained from the elemental analysis helps to consider the formation of a set of possible intrinsic lattice defects, including vacancies, self-interstitials, antisites, and defect complexes. Due to these results and the experimentally obtained values of the band gap within 1.0−1.37 eV, a deviation from the calculated band gap values is estimated in the range of 1.0−1.5 eV. It is suggested which defects can have an influence on such a band gap change. Also, on comparing the experimental Raman spectra of CZTSSe with the theoretical modeling results, an excellent agreement is obtained for the main Raman bands. The proposed theoretical approach allows to estimate the values of concentration of atoms (S or Se) for CZTSSe solid solution directly from the experimental Raman spectra. Thus, the visualization of morphology and the proposed theoretical approach at various x values will help for a deeper understanding of the CZTSSe structure to develop next-generation solar cells.
Electronic Band Structure of Copper Zinc Tin Sulphide (Cu 2 ZnSnS 4).
IOSR Journals , 2019
Cu 2 ZnSnS 4 (CZTS), made entirely of abundant materials, has attracted a great interest due to its potential applications in sustainable thin-film solar cell devices. The electronic band structure of kesterite Cu 2 ZnSnS 4 compound has been calculated using the pseudo-potential method. Projector augmented waves (PAW) within the density functional theory (DFT) was used in all calculations using local density approximation (LDA) for one calculation and inclusion of potential correlation term, U to LDA (i.e LDA + U) in another calculation. The results predicted Cu 2 ZnSnS 4 to be a p-type semiconductor with bandgap value for (1) LDA as 0.039 eV and (2) LDA + U as 1.83 eV. This bandgap value of 1.83 eV is in agreement with experimental results and it confirmed the material as a good absorber layer for solar cells. The density of states (DOS) showed that the conduction band was mainly contributions from Sn-5p and Zn-4s orbitals. It is recommended that the orbital independent term, U be added to LDA during calculations because it improves the bandgap value.
Chemistry of Materials, 2016
A new solution based route for depositing Cu 2 ZnSnS 4 (CZTS) thin films is described, focusing on the effects of Sb and Na codoping. X-ray diffraction and Raman spectroscopy confirm formation of the kesterite phase with a measurable improvement in crystallinity upon doping. A sharp band gap absorption edge at 1.4 eV is determined from diffuse reflectance measurements, while improvement in the photoluminescence yield and sharpening of the band-to-band emission spectra are observed in the presence of Na and Sb. The performance of devices with the configuration glass/Mo/ CZTS/CdS/i-ZnO/ZnO:Al/Ni−Al and total area of 0.5 cm 2 is reported. Analysis of over 200 cells shows that introduction of Na and Sb leads to an increase of the average power conversion efficiency from 3.2 ± 0.6 to 5.2 ± 0.3%. The best cell with efficiency of 5.7% is obtained upon Na and Sb doping, featuring 14.9 mA cm −2 short-circuit current, 610 mV open circuit voltage, and 63% fill factor under simulated AM 1.5 illumination. This performance ranks among the highest in pure sulfide CZTS cells. We propose that the improvement in crystallinity and cell performance is linked to the formation of alkali antimony chalcogenides flux during the annealing step, in addition to Sb and Na decreasing disorder in specific lattice positions of the CZTS unit cell.