CuIn(Se,S) 2 Absorbers Processed using a Hydrazine-Based Solution Approach
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1123-P06-03-F07-03
CuIn(Se,S)2 Absorbers Processed using a Hydrazine-Based Solution Approach Wei Liu,1 David B. Mitzi,1 S. Jay Chey1, Andrew Kellock2 1
IBM T. J. Watson Research Center, P. O. Box 218, Yorktown Heights, NY 10598 IBM Almaden Research Center, 650 Harry Rd, San Jose, CA 95120 Email: [email protected] 2
ABSTRACT With tunable bandgap and demonstrated high efficiency, the chalcopyrite CuInSe2 and its alloys have shown great potential as absorbers for single and multi-junction solar cells. However, the current deposition techniques mostly rely on expensive vacuum-based processing or involve complicated precursor solution preparation. These higher-cost absorber preparation processes make it difficult to commercialize this technology. In this work, CuInSe2-xSx (CIS) absorbers are deposited using a simple hydrazine-based solution process. Precursor solutions were prepared by dissolving the component metal chalcogenides and chalcogen in hydrazine, forming homogeneous solutions containing adjustable concentrations of desired elements mixed on a molecular level. These precursor solutions are then spin coated on substrates followed by a heat treatment in an inert environment to produce high quality CIS thin films. Significantly, no post deposition selenization process is required using this technique. Laboratory scale devices with conventional glass/Mo/CIS/CdS/i-ZnO/ITO structure have been fabricated using CIS absorbers deposited via this process. For the baseline low-bandgap CIS system with no Ga added (to compare with our previously reported results with Ga incorporated), AM1.5G conversion efficiency of as high as ~9% has been achieved for devices with 0.45 cm2 effective area. INTRODUCTION To make CuInSe2 and its alloy a feasible photovoltaic (PV) technology, traditional vacuum-based deposition techniques face many challenges including high cost and low throughput. Current solution-based techniques attempt to address these issues, but often run into the same issues. For example, in some cases, multiple steps are required to prepare the precursor particles for solution-based deposition and undesirable oxides have to be introduced into the precursor and later taken out of the system at the cost of an extra reduction and/or selenization process [1]. With hydrazine as solvent [2-4], we can develop a much simpler process and only incorporate the necessary components of CuIn(Se,S)2 into the precursor. For this method, precursor solutions were prepared by dissolving relevant metal chalcogenides and chalcogen in hydrazine, producing homogenous solutions with desired elements mixed on a molecular level. CIS thin films with good crystallinity are demonstrated by simply spin-coating the mixed precursor solutions onto Mo-coated soda-lime glass under an inert atmosphere, followed by a simple heat treatment on a hot plate. PV devices with glass/Mo/CIS/CdS/i-ZnO/ITO structure were fabricated and with efficiencies of as high as ~9% being achieved for devices with 0.45 cm2 effective area. Compared with our previously published
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