研究目的
Investigating the crystallographic, optical, and electronic properties of (Cu1-xLix)GaS2 solid solution samples synthesized by mechanochemical process and sequential heating.
研究成果
Single-phase chalcopyrite-type (Cu1-xLix)GaS2 solid solution samples were synthesized for the composition with 0.00 ≤ x ≤ 0.20. The lattice constant a of tetragonal (Cu1-xLix)GaS2 increased with increasing Li content, x, but the lattice constant c decreased with increasing Li content. The band-gap energy of (Cu1-xLix)GaS2 monotonically increased from 2.44 eV of CuGaS2 (x = 0.00) to 2.54 eV of (Cu0.80Li0.20)GaS2 (x = 0.20). The VBM level of the (Cu1-xLix)GaS2 solid solution decreased with increasing Li content, x, while the CBM level was approximately constant. Li doping in CuGaS2 is useful for decreasing the VBM of the (Cu1-xLix)GaS2 absorber and increasing the band-gap energy of the CuGaS2 absorber without increasing the CBM level.
研究不足
The single-phase region of chalcopyrite-type (Cu1-xLix)GaS2 solid solution is limited to compositions with 0.00 ≤ x ≤ 0.20. The band-gap energy estimated from the diffuse reflectance spectra of the powder was about 0.05 eV smaller than that estimated from the transmittance spectra of the film.
1：Experimental Design and Method Selection
Synthesis of (Cu1-xLix)GaS2 solid solution samples by mechanochemical process and sequential heating at 550oC in 5% H2S/N2 gas atmosphere. Crystal structures were analyzed by X-ray powder diffraction (XRD), and their crystallographic parameters were refined by Rietveld analysis.
2：Sample Selection and Data Sources
Starting materials such as elemental Cu, Ga, S and dilithium sulfide Li2S were weighed to give a molar ratio of (Cu1-xLix)GaS2 (x = 0.00, 0.05, 0.10, 0.15, 0.20, 0.25, 0.30, 0.35).
3：List of Experimental Equipment and Materials
Planetary ball milling (Fritsch premium line P-7), X-ray diffractometer (Rigaku RINT-2400), UV-vis-NIR spectroscopy (JASCO V-670DS), Photoemission yield spectroscopy (Bunkoukeiki BIP-KV201).
4：Experimental Procedures and Operational Workflow
Mixed powders were heated at 550oC for 30 min in 5% H2S/N2 gas atmosphere in a single-zone silica tube furnace. XRD measurements for Rietveld analysis were carried out using an X-ray diffractometer. Band-gap energies were determined from diffuse reflectance spectra measured by UV-vis-NIR spectroscopy. Ionization energies were measured by photoemission yield spectroscopy.
5：Data Analysis Methods
Crystallographic parameters such as lattice constants a, c, and x-coordinate of the S atom for chalcopyrite-type (Cu1-xLix)GaS2 were refined by Rietveld refinement using Reflex Plus software. Band-gap energies were determined by Tauc plot of the diffuse reflectance spectra. Ionization energies were determined by linear fitting of the Is 1/3 vs. hν plot.
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