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In this study, we investigated the impact of incorporating graphene with Ga-doped ZnO (GZO) when employing them as a TCO layer on Si-based solar cell. GZO thin films with various thicknesses (50-450 nm) were fabricated by the sputtering method using a single target. The aim here was to determine the GZO film with the optimum thickness to incorporate it with single layer graphene as TCO. This thickness was found to be 350 nm as that was the best crystalline quality found in the Opattern. Further, this sample had the lowest sheet resistance and highest transmission values as confirmed by electrical (sheet resistance), and optical characterizations (transmission). Topographic (SEM and AFM), electrical (resistivity and carrier concentration) measurements were also conducted on the same sample. The graphene film grown on copper in a CVD system was then transferred on top of this sample to fabricate the hybrid TCO structure. We found that graphene integrated GZO hybrid TCO film showed higher sheet resistance due to high sheet resistance of graphene and similar optical properties thanks to high optical transmission of graphene. Employing graphene-based TCO layer in the solar cell resulted in higher open-circuit voltage, consequently improving the conversion efficiency from 10.0% to 11.2%. (c) 2021 Elsevier Ltd. All rights reserved.

In this study, Cu2ZnSnS4 (CZTS) thin films were synthesized by a two-stage process. In the first stage, CuSn/Zn/Cu (E-type) and CuSn/ZnS/Cu (B-type) stacked films were formed using the sputtering method. In the second stage, precursor films were annealed in sulfur atmosphere utilizing various annealing temperatures (500, 525, 550 and 575 degrees C) employing the Rapid Thermal Processing (RTP) method. The EDX measurements demonstrated that almost all the samples had Cu-poor and Zn-rich compositions, as targeted. The XRD patterns of all the CZTS samples were dominated by diffraction peaks of the kesterite CZTS phase. In addition to CZTS phase, Cu-S/Sn-S based secondary phases in all E-type CZTS thin films and some B-type CZTS samples annealed at lower temperatures (500 and 525 degrees C) were observed. The samples annealed at above 525 degrees C revealed purer crystal structure in terms of secondary phases and they have more promising crystallite size in both types of CZTS thin films. The Raman spectroscopy measurements confirmed the formation of kesterite CZTS phase and distinguished the formation of Cu2SnS3 (CTS) phase for some samples. The samples annealed at 550 degrees C presented purer structure for potential solar cell application. The SEM surface and cross-section images of all CZTS samples displayed dense and polycrystalline structures but samples annealed at 550 degrees C presented a larger-grained surface and crosssection structure in both types of CZTS films. PL spectra of the B-type CZTS samples exhibited a purer band structure with respect to E type CZTS samples according to their PL band values. The best solar cell performance was achieved with CZTS thin film prepared using CuSn/ZnS/Cu stack annealed at 550 degrees C temperature with 252 mV, 32 mA/cm(2), and 3.79% parameters. (C) 2021 Elsevier Ltd. All rights reserved.

Cu2ZnSnS4 (CZTS) thin films are commonly used as an absorber layer in the thin film solar cell structure. In this study, CZTS thin films were produced by sulfurization of stacked precursor films that is prepared by deposition of Cu, Zn, SnS, ZnS films on glass substrate using sputtering method. The sequential sputter deposition was performed to obtain two distinct stacked precursors, Cu/SnS/Zn/Cu and Cu/SnS/ZnS/Cu respectively. Afterwards, annealing process was implemented at various reaction temperatures (500–575 °C) for 1 min utilizing rapid thermal processing (RTP). The EDX measurements revealed that all the prepared CZTS samples had Cu-poor and Zn-rich composition that are non-stoichiometric chemical composition. This non-stoichiometric composition is important for high efficient CZTS based solar cells. XRD measurements revealed that all patterns are dominated by diffraction planes of kesterite CZTS. The CuS, Cu2S and SnS2 secondary phases also were detected in the XRD pattern of some CZTS films. Raman spectroscopy measurements verified formation of kesterite CZTS phase for all films and picked out CTS phase for some samples prepared using Cu/SnS/Zn/Cu precursor films. The surface microstructure of the films that were obtained through SEM displayed polycrystalline surface structure. Room temperature PL emission spectra of the films showed broad peak at around 1.37–1.38 eV, which is near to the optical band gap of kesterite CZTS structure. Electrical characterization of the samples demonstrated that B-525 CZTS thin film has more suitable electrical resistivity and carrier concentration values for CZTS based solar cell applications.