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Solar cell technologies using I-III-VI2 chalcopyrite semiconductors have made rapid progress in recent years. Conversion efficiencies for polycrystalline Among ternary chalcopyrite semiconductors, CuInS2 may be the most promising material for photovoltaic applications due to the bandgap of 1.5 eV which perfectly matches the solar spectrum for energy conversion. However, the conversion efficiency of the CuInS2 based solar cells are so far limited to around 12 %. One reason for this relatively low efficiency is that the physical properties of CuInS2 are not accurately known because high-quality single crystal growth of CuInS2 is difficult in comparison to CuInSe2 and CuGaSe2.
In this work, the CuInS2 crystals are grown by Hot-Press (HP) method at 400 ~ 700 °C for 1 h under high pressure (10 ~ 100 MPa) and Cu/In ratio of 0.6~1.5. One of the advantages of the HP method is that a crystal growth is easy at low temperature. The sizes of the samples are 2 cm in diameter. The crystal structures and lattice constants were examined by X-ray diffraction (XRD) measurement. The conduction types and compositions of the all samples were obtained by Hall measurement and electron probe microanalysis (EPMA), respectively.
A stoichiometric sample indicates chalcopyrite structure, nearly stoichiometry and n-type by means of XRD, EPMA and Hall measurements, respectively. However, Cu-rich sample indicates p-type. It is assumed that Cu atoms in In site enhances to conduction type. Lattice constants of a and c axes increase and decrease with increasing the Cu/In ratio. Furthermore, grain size increases with increasing the Cu/In ratio. We can control the conduction type, lattice constants and grain size with changing the Cu/In ratio.
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