A novel technique for synthesis of CuGaS 2 solar energy thin film is presented. It is associated with double pulse electrodeposition of Cu-Ga precursor layer followed by thermal annealing treatment in sulfur atmosphere. The influence of several flexible parameters including pulse deposition potential and agitation rate on the compositions, crystal structure and morphology of the films were investigated. A relative negative shift of the higher pulse deposition potential results in the increasement of Ga content. A higher agitation rate results in higher Cu/Ga ratio and the emergence of CuS secondary phase after annealing in sulfur atmosphere. The crystal size increases with decreasing the higher pulse deposition potential. Several characterization methods including X-ray diffraction (XRD), scanning electron microscope (SEM), energy diffraction spectrum (EDS), ultraviolet-visible (UV-vis) spectra, impedance spectroscopy, and Raman spectrum are used to characterize the synthesized CuGaS 2 polycrystalline thin films. Based on the experimental results, a probable formation mechanism of the CuGaS 2 thin films was proposed and briefly discussed.The broad bandgap and high absorption coefficient offered by the chalcopyrite semiconductor materials make them attracting considerable attention on application in photovoltaic solar cells, 1 light emitting diodes, 2 hydrogen production, 3 and various nonlinear optical devices. 4 Solar cells based on polycrystalline Cu(In,Ga)Se 2 absorber layers have demonstrated the highest power conversion efficiencies of up to 20.3% in laboratory among the thin film technology. 5 However, a toxic selenium gas treatment limited large scale production. Many studies were presently focused on the exploration of chalcogenide compounds Cu(In,Ga)S 2 based solar cells which have reached a limited efficiency of below 13%. 6 For a further promotion on conversion efficiency, tandem solar cell structures are currently subject of intensive research. The ternary compound CuGaS 2 as a member of the chalcopyrite family has a bandgap energy (Eg) of around 2.45 eV and has been considered as a promising material for high efficiency tandem solar cells. 7 It also bears perspectives as a Cd-free window material for Cu(In 1−x Ga x )Se 2 type solar cell. 8 Meanwhile, it possesses a bandgap close to the optimum for the realization of a thin-film intermediate-band solar cell (IBSC), theoretically able to reach value of energy conversion efficiency above 46% under sun irradiation. 9 Numerous approaches developed for the fabrication of CuGaS 2 , such as metal-organic chemical vapor deposition, 10 modulated flux deposition, 11 vacuum evaporation 12,13 and molecular beam epitaxy, 14 are not suitable for large-scale production due to the expensive cost. Electrodeposition method is an appealing technique that offers lowcost equipment, efficient material utilization and scalability for largescale deposition, and has widely been employed for the deposition of elemental, binary, ternary or even more complex compound thin films....
CuGaS2 solar energy thin film is fabricated with electrochemical deposition of precursor from deep eutectic solvent (DES) based on choline chloride and urea (commercially known as Reline) to eliminate the interference of hydrogen evolution reaction (HER). The process involves electrodeposition of Cu-Ga precursor on molybdenum substrate from Reline and subsequential annealing in sulfur vapor. The formation of CuGa2 alloy in precursor is observed and pure ternary chalcopyrite CuGaS2 phase in good polycrystalline structure without secondary phase is obtained after thermal treatment. The influence of applied deposition potential on the crystalline phase, morphology, compositions and carrier concentration of the films were investigated. The Cu/Ga ratio decreases with decreasing the deposition potential benefiting the formation of a pure crystallized CuGaS2 thin film. A relative positive deposition potential results in a larger crystalline size benefitting the photoelectrical conversion. Impedance spectroscopy test demonstrates the semiconductor property of the synthesized CuGaS2 polycrystalline thin film is p-type and the carrier concentration increases with negative shift of deposition potential.
A new synthetic route for Cu(In,Ga)S2 (CIGS) absorber thin film is presented. It involves the one-step electrodeposition of Cu-Ga-S precursors on indium tin oxide (ITO) substrate from alcohol solution followed by thermal annealing treatment to incorporate In, diffused from the ITO substrate. Several characterization methods including XRD, SEM, EDS, TEM and absorption spectra are used to characterize the synthesized quaternary Cu(In,Ga)S2 (CIGS). Pure quarternary chalcopyrite Cu(In,Ga)S2 (CIGS) phase in good polycrysralline structure without secondary phase is obtained after annealing. The influence of deposition potential on the morphology and optical properties of the films is investigated. A relative positive deposition potential results in a larger crystalline size benefitting the photoelectrical conversion. A possible growth mechanism for explaining the formation of Cu(In,Ga)S2 (CIGS) thin films is proposed and briefly discussed. The electrochemical photoresponse of the Cu(In,Ga)S2 (CIGS) thin films indicating a p-type semiconductor implies its potential application in photovoltaic devices.
Germanium carbide (Ge1−xCx) films have been prepared by radio frequency (RF) reactive sputtering of a pure Ge(111) target in a CH4/Ar mixture discharge, and their composition, chemical bonding, optical and mechanical properties have been investigated as a function of RF power. The relationship between the chemical bonding and the optical and mechanical properties of the Ge1−xCx films has been explored. The results show that the refractive index of Ge1−xCx films increases from 1.9 to 3.2 and the optical gap decreases from 1.9 to 1.0 eV as RF power increases from 80 to 250 W, which is due to an increase in the germanium content with increasing RF power. Also, it is found that the hardness of Ge1−xCx films increases with increasing RF power, which can be attributed to an increase in the fraction of sp3 Ge–C bonds at the expense of the sp2 C–C bonds in the Ge1−xCx films.
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