Fabrication of (Cu,Ag)InSe 2 Thin films by a Combination of Mechanochemical and Screen Printing/Sintering Processes
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1012-Y03-15
Fabrication of (Cu,Ag)InSe2 Thin Films by a Combination of Mechanochemical and Screen Printing/Sintering Processes Syuusuke Nomura, Yoshihiro Matsuo, and Takahiro Wada Department of Materials Chemistry, Ryukoku University, Seta, Otsu, 520-2194, Japan ABSTRACT We successfully prepared (Cu1-XAgX)InSe2 solid solution with 0 ≤ x ≤ 1.0 by a mechanochemical process without any additional heating. The obtained fine powder was suitable for screen-printing. Particulate precursors were deposited in a thin layer by a screen-printing technique and then the porous precursor layer was sintered into a dense polycrystalline film by atmospheric-pressure firing. The crystal structures of the powder and the film were analyzed by x-ray diffraction and the microstructure of the film was observed in an SEM. For the (Cu1-XAgX)InSe2 films with x ≤ 0.2, the (Cu,Ag)InSe2 films had a good microstructure for the solar cell absorbers.
INTRODUCTION CuInSe2 (CIS) and its solid solution such as Cu(In,Ga)Se2 (CIGS) are excellent thin-film photovoltaic materials. The CIGS films are usually deposited by physical vapor deposition (PVD) or “sputtering and selenization”. However, vacuum-based deposition processes, such as PVD and “sputtering and selenization” are complex and expensive. Therefore, we have proposed non-vacuum deposition technique for the CIGS thin films. We have fabricated CIGS thin films by a combination of mechanochemical and screen printing/sintering processes [1]. Our preliminary CIGS solar cell showed an efficiency of 2.7%. The combination of mechanochemical and screen printing/sintering processes has some advantages for mass production of CIS solar cells, such as high energy efficiency, high productivity and short processing cycle times. CIS has a band-gap (Eg) of 1.04 eV which is a little smaller than the ideal value of 1.40 eV for an absorber of solar light. Usually, a solid solution between CIS and CuGaSe2(CGS) with Eg of 1.68 eV, Cu(In,Ga)Se2 (CIGS) was used for high efficiency thin film solar cells. However, it was known that the incorporation of Ga in CuInSe2 suppressed a growth of crystals. AgInSe2 (AIS) has a wider bang gap (Eg) of 1.24 eV than the Eg of CIS [2]. The AIS has a lower melting point of 780oC than those of CIS, 1020oC and CGS, 1080oC [3]. We think that a solid solution between CIS and AIS, (Cu,Ag)InSe2 (CAIS) can be sintered more easily than the CIGS. In this study, we prepared (Cu1-XAgX)InSe2 solid solution powder by the mechanochemical process. Particulate precursors ink was prepared by a mixing of the obtained (Cu1-XAgX)InSe2 powder with an organic solvent. We fabricated (Cu1-XAgX)InSe2 films by the screen printing and sintering process.
EXPERIMENTAL PROCEDURES Elemental powders such as Cu, Ag, In, Se were weighted to give a molar ratio of
Cu:Ag:In:Se = (1-X) : X : 1 : 2. The (Cu1-XAgX)InSe2 (CAIS) powder was synthesized from elemental powders by a planetary ball milling in N2 gas atmosphere without any additional heating. The ball-to-powder weight ratio was maintained at 5:1. The milling was
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