Optimization of sulfurization time and temperature for fabrication of Cu2ZnSnS4 (CZTS) thin films

In this study, growth of CZTS thin films was performed by sputter deposition of metallic precursor layers followed annealing process at different sulfurization temperatures and times. In the first stage of the study, effect of the reaction temperature for 1 s sulfurization time was investigated. XRD pattern of the sample sulfurized at 560 °C showed purer XRD pattern and better crystalline quality. Zn and Sn loss was observed for reacted samples at 540 and 580 °C. SEM images of CZTS560-1 samples revealed purer and molten-like surface structure. Optical band gap values were found 1.45 eV that are not influenced by sulfurization temperature. In the second stage, effect of the sulfurization time for sulfurization temperature at 560 °C was examined with addition of electrical characterization to the previous characterization methods. EDX results demonstrated that Zn-loss took place at higher dwell time of reaction (300 s). XRD data showed that increasing the sulfurization time above 1 s enhances the crystalline quality and contributes to form much purer CZTS structure. Raman spectroscopy confirmed presence of CZTS phase. Optical band gap values (1.45–1.48 eV) and electrical properties of the CZTS thin films were strongly influenced by [Cu]/[Sn] atomic ratio and presence of Cu–S based secondary phase. © 2018 Elsevier Lt

Structural, optical and Schottky diode properties of Cu2ZnSnS4 thin films grown by two-stage method

CZTS thin film was prepared by a two-stage process comprising sputter deposition of metallic Cu, Zn, and Sn layers followed annealing treatment of the metallic precursors in a sulfur atmosphere at 560 °C for 3 min. The CZTS thin film was investigated in the way of structural, optical and electrical properties. The XRD pattern of Cu-poor and Zn-rich CZTS thin film was dominated by characteristic peaks of kesterite CZTS planes. Raman spectra of the film ensured formation of kesterite CZTS phase and displayed formation of CTS and ZnS phases. Dense and polycrystalline surface features were observed in SEM images of CZTS thin film. Band–band transitions was not observed due to the probable concentration of deep acceptor levels in this material. The diode parameters of Mo/CZTS/Al structure such as ideality factor, barrier height and serial resistance were calculated employing temperature dependent I–V characteristics of Mo/CZTS/Al diode structure. © 2019, Springer Science+Business Media, LLC, part of Springer Nature

Growth of Cu 2 ZnSnS 4 (CZTS) thin films using short sulfurization periods

In this study CZTS thin films were grown by a two-stage process that involved sequential sputter deposition of metallic Cu, Zn, and Sn layers on Mo coated glass substrates followed by RTP annealing at 530 and 560 °C for various dwell times (1, 60, and 180 s). CZTS thin films obtained by reaction at different sulfurization temperatures and reaction times were characterized employing XRD, Raman spectroscopy, SEM, EDX, and photoluminescence. It was observed that it is possible to obtain Cu-poor and Zn-rich CZTS thin films with short dwell time of reactions. XRD pattern and Raman spectra of the films showed formation of kesterite CZTS structure and some secondary phases such as CuS, SnS, SnS 2 . The full-width-at-half-maximum (FWHM) values extracted from the (112) diffraction peaks of the CZTS thin films showed that extension of the sulfurization time provides better crystalline quality except for the CZTS560-60 thin film. SEM surface microstructure of the films displayed non-uniform, dense, and polycrystalline structure. The optical band gap of the films as determined by photoluminescence was found to be about 1.36-1.38 eV. © 2019 IOP Publishing Ltd

Growth and characterization of Cu2SnS3 (CTS), Cu2SnSe3 (CTSe), and Cu2Sn(S,Se)3 (CTSSe) thin films using dip-coated Cu–Sn precursor

Ternary compounds Cu2SnS3, Cu2SnSe3 and Cu2Sn(S,Se)3 thin films used in thin film solar cell applications were prepared at the first time by such a two-stage process that includes dip-coating of Cu–Sn precursors as distinct from vacuum-based fabrication methods followed by sulfurization/selenization of prepared precursors via rapid thermal processing at 550 °C. All prepared thin films revealed Cu-poor composition. X-ray diffraction and Raman spectra of the samples showed that Cu2SnS3 and Cu2SnSe3 thin films had a monoclinic structure as a dominant phase and additionally some secondary phases such as tetragonal Cu2SnS3 and orthorhombic Cu3SnS4. However, the tetragonal and orthorhombic phases had more impact on Cu2Sn(SSe)3 thin film. Compact, dense, and small grained surface morphologies were obtained for the Cu2SnS3 and Cu2Sn(SSe)3 thin films, while the surface morphology of the Cu2SnSe3 thin film had larger grained surface morphology. The Cu2SnS3 thin film demonstrated higher transmittance (~ 65%) and two different absorption edges that indicates formation of two band gap energy. Band gap values of Cu2SnS3, Cu2Sn(SSe)3 and Cu2SnSe3 thin films were found 0.97 eV (and 1.51 eV), 1.25 eV and 0.78 eV, respectively. The lowest resistivity (2.48 × 10-1 ? cm) and the highest carrier concentration (1.64 × 1019 cm-3) values were observed for Cu2Sn(SSe)3 thin film. © 2019, Springer Science+Business Media, LLC, part of Springer Nature.Recep Tayyip Erdogan ÜniversitesiThis work was supported by the research fund of Recep Tayyip Erdogan University, Rize, Turkey, under Contract No. FDK-2018-96

CZTS layers formed under sulfur-limited conditions at above atmospheric pressure

In this study CZTS thin films were grown by a two-stage process that involved sequential sputter deposition of metallic Cu, Zn, and Sn layers on Mo coated glass substrates followed by RTP annealing in a sulfur atmosphere at background gas pressures in the range of 1–2 atm. Sulfurization was carried out in a mini reaction volume that provided a relatively S-limited environment. Reacted films were characterized using XRD, EDX, SEM, photoluminescence and Raman spectroscopy. It was found that, under the S-limited regime provided in these experiments the Cu-S secondary phase formation was most extreme in the sample grown at 1.5 atm, whereas films grown at lower and higher pressures showed much smaller degree of phase separation. Reaction at 2 atm yielded a compound film that was the closest to the initial precursor in terms of its composition. SEM micrographs showed rough morphology and polycrystalline structure that changed with the sulfurization pressure. The optical band gap of the films as determined by photoluminescence was found to be about 1.37 eV. These experiments demonstrated the importance of the sulfurization pressure as well as the size of the reactor internal volume in determining secondary phase formation in two-stage processed CZTS layers. © 2018 Elsevier Lt

Influence of pre-annealing Cu-Sn on the structural properties of CZTSe thin films grown by a two-stage process

In this study CZTSe thin film were synthesized by a two-stage process that included sequential sputter deposition of Cu and Sn layers forming a Cu/Sn structure, pre-annealing the Cu/Sn structure at 200–380 °C for some of the samples, sputtering of additional Zn and Cu over the Cu/Sn structure, evaporation of a Se cap forming a Cu/Sn/Zn/Cu/Se precursor film, and exposing the precursor film to high temperature annealing treatment at 550 °C for 15 min to form the compound. The results of the characterization carried out on the compound layers revealed that the phase content, composition and microstructure of these layers changed noticeably depending on whether or not a pre-annealing step was utilized. Although XRD studies suggested presence of secondary phases, especially in the non-pre-annealed samples, the data was dominated by kesterite CZTSe phase reflections. Raman spectra of the films verified the formation of kesterite CZTSe structure and some other phases, which were determined to be SnSe 2 and possibly ZnSe. SEM micrographs showed denser structure in the pre-annealed samples. © 2018 Elsevier Lt

Cu2ZnSnS4 based thin films and solar cells by rapid thermal annealing processing

In this study, kesterite Cu2ZnSnS4 (CZTS) absorber layers were fabricated by DC magnetron sputtering deposition of metallic Cu-Zn-Sn precursors, followed by an annealing treatment in sulfur vapor atmosphere at 600 °C for 3 min using rapid thermal processing (RTP). Three types of stacked metallic films were prepared and included pre-annealing of Cu-Sn stacks in order to induce preferential Cu-Sn alloying. The chemical composition of the sulfurized films was obtained by X-ray fluorescence (XRF) before and after etching the samples in KCN solution. All CZTS thin films are found to be Cu-poor and Zn-rich. Structural characterizations were performed by X-ray diffraction (XRD) and Raman spectroscopy to investigate the impact of pre-annealing on the structural properties of the precursors and final CZTS films. Glow discharge optical emission spectroscopy (GDOES) shows that pre-annealing of the precursors can improve depth homogeneity of the CZTS films. Photoluminescence spectra and the optical band gap energy values are compatible with literature. Selected samples were processed to solar cells and characterized.Turkish Council of Higher Education (YOK