Fabrication of Cu(In,Ga)Se 2 films by a combination of mechanochemical synthesis, wet bead milling, and screen-printing/
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1165-M05-13
Fabrication of Cu(In,Ga)Se2 films by a combination of mechanochemical synthesis, wet bead milling, and screen-printing/sintering process J. Kubo1, Y. Matsuo1, T. Wada1, A. Yamada2,3, and M. Konagai2,3 1 Department of Materials Chemistry, Ryukoku University, Japan 2 Department of Physical Electronics, Tokyo Institute of Technology, Japan 3 Photovoltaic Research Center (PVREC), Tokyo Institute of Technology, Japan ABSTRACT We prepared fine Cu(In,Ga)Se2 (CIGS) powder suitable for screen printing using a mechanochemical synthesis and wet bead milling. Particulate precursors were deposited in a layer by a screen-printing technique, and the porous precursor layer was sintered into a dense polycrystalline film by atmospheric-pressure firing in an N2 gas atmosphere. The microstructure of CIGS powder and fired CIGS film were observed in an SEM. The wet bead milling was effective for the reduction and homogenization of the average grain size of CIGS powder. The CIGS grains in the film were well sintered and the size of CIGS grains was as large as about 2 μm. The CIGS solar cell showed an efficiency of 3.1%, with Voc of 0.279 V, Jsc of 28.8 mA/cm2 and FF of 0.386. INTRODUCTION Recently, Cu(In,Ga)Se2(CIGS) thin solar cells with power conversion efficiencies approaching 20% have been demonstrated [1]. However, the vacuum-based processes used to deposit the CIGS absorber layers in the high efficiency CIGS solar cells pose financial and technological barriers to the production of low-cost photovoltaic (PV) modules. Therefore, various non-vacuum deposition methods for fabricating CIGS films have been developed: (1) electro-deposition, where chemical reactions in a solution lead to the coating of an immersed substrate [2,3]; (2) processes that coat molecular precursor solutions onto a substrate by mechanical means [4, 5]; and (3) particulate-based processes that use solid particles dispersed in a solvent to form an ink, which can be coated onto a substrate [6-8]. We studied the fabrication of CIGS films by one of the particulate-based processes: a combination of mechanochemical and screen printing/sintering processes [8, 9]. CIGS powder suitable for screen-printing was prepared using a mechanochemical process (MCP) [10, 11]. MCP is a process that induces physical and chemical changes by mechanical energy, such as pulverization, friction or compression. This method has some advantages for mass production of CIGS solar cells, such as high energy efficiency, high productivity and short processing cycle times. The CIGS solar cells with an Al grid/B-doped ZnO/i-ZnO/CdS/CIGS/ Mo/soda-lime glass structure showed an efficiency of 2.7% [8].
In this study, to obtain a higher energy conversion efficiency of the CIGS solar cells fabricated by a combination of mechanochemical and screen printing/sintering processes, we studied the preparation process of particulate precursor ink suitable for screen printing. We tried to prepare the particulate precursor ink by wet bead milling, which is usually used for dispersing nanoparticles in
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