Synthesis of Si Nanowires by Electroless Etching Technique and Their Integration Into I-III-VI 2 Thin Films For Solar Ce
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Synthesis of Si Nanowires by Electroless Etching Technique and Their Integration Into IIII-VI2 Thin Films For Solar Cells H. Karaagac1, M. Parlak2 and M. Saif Islam1 Department of Electrical and Computer Engineering, University of California at Davis, CA, 95616, USA 2 Department of Physics, Middle East Technical University, 06531 Ankara, Turkey
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ABSTRACT Si nanowires (NWs) have been fabricated by Ag-assisted electroless etching technique using an HF/AgNO3 aqueous solution. Scanning electron microscopy (SEM) measurements have revealed that a highly dense array of Si NWs with length of ~1.4 μm is formed over the surface of both n-type and p-type Si (100) substrates. Following the fabrication of Si NWs, electronbeam evaporated p-type AgGa0.5In0.5Se2 thin film was deposited on the n-type Si NWs to form pn heterojunction solar cells. The fabricated solar cells yield a 5.50% power conversion efficiency under AM (1.5) illumination. INTRODUCTION The vast majority of today’s commercial photovoltaic (PV) market is still based on silicon (Si) material. Silicon is the leading photovoltaic material due to several advantages over the other PV materials, such as its abundance, good stability, high reliability and processing benefits. For the fabrication of highly efficient Si solar cells, high quality Si single crystalline materials are required, which brings with it the necessity of extensive purification process that greatly increases the cost. Thin film solar cells are being considered as a potentially low-cost route to fabricate highly efficient solar cells. They have been regarded as potential candidates that enable efficiencies that can cope with crystalline-Si solar cells. In the past three decades, researches have been focused on using different materials in thin film solar cells, such as polycrystalline Si, amorphous Si, polymers, II-VI and I-III-VI2 compounds. In particular, chalcopyrite (I-III-VI2) compound are promising candidates for the realization of highly-efficient solar cells based on the p-n heterojunction with II-VI semiconductors, which has similar crystal structure contributing to reduce the lattice miss-match in the structure. Cu-III-VI2 and Ag-III-VI2 compounds are wellknown groups of chalcopyrites which have considerably high absorption coefficient (105 cm-1) and optimum band gap energy, well matched to the optimum part of solar spectrum [1]. In addition to thin film solar cells, nanowires based solar cells have been proposed as potential structures to lower the manufacturing cost and improve the efficiency of solar cells. A solar cell based on nanowires enables both light trapping and efficient collection of the photogenerated carriers which addresses the key challenges in improving the efficiency of a solar cell [2]. Although thin film and nanowire based solar cells were extensively studied separately for a broad range of material with different geometries, most of these studies were not focused on combining them. Because of its well-known properties and its highly developed technology,
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