AVS 52nd International Symposium
    Thin Films Monday Sessions
       Session TF+EM-MoM

Paper TF+EM-MoM4
Growth of CIGSS Thin Film Solar Cells on Flexible Stainless Steel Substrates of Various Thicknesses

Monday, October 31, 2005, 9:20 am, Room 306

Session: Thin Films for Photovoltaic and Energy Applications
Presenter: A. Kadam, University of Central Florida
Authors: A. Kadam, University of Central Florida
A. Jahagirdar, University of Central Florida
N.G. Dhere, University of Central Florida
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The article presents the effect of surface roughness and thicknesses of stainless steel(SS) substrates on the growth behavior of CuIn@sub 1-x@Ga@sub x@Se@sub 2-y@S@sub y@(CIGSS) absorber thin film solar cells. The work was carried out on 430 grade SS of thicknesses 25 µm, 50 µm and 127 µm. Surface roughness gradually decreased from 254 Å for 25 µm to 62.3 Å for 127 µm substrate. Thinner foil has higher surface roughness as it required more processing steps. Deposition sequence was Mo/SS/Mo/CIGSS/CdS/i:ZnO/ZnO:Al/Ni/Al. Mo back contact and Cu-Ga-In metallic precursors were deposited by DC magnetron sputtering. Mo was deposited on both the sides of SS to prevent the reaction of selenide and sulfide gases with SS during processing. Mo was deposited in a three-layer sequence. Mo layer deposited at low DC power and high argon gas pressure develops tensile stress while that deposited at high power and low pressure exhibits compressive stress. Tensile layer was sandwiched between two compressive layers to reduce the overall stress and to build the thickness of 500 nm. Identical parameters were used for deposition of metallic precursors on all three substrates. The elemental stack was selenized at 400@super o@C for 10 minutes followed by sulfurization at 475@super o@C for 20 minutes. CdS, n-type hetero-junction partner was deposited by chemical bath deposition. Window bilayer of i:ZnO and ZnO:Al were deposited by RF magnetron sputtering and Ni/Al contact fingers were deposited by e-beam evaporation. The crystal structure, surface morphology, chemical variation and cell efficiency were studied using the characterization technique such as x-ray diffraction, scanning electron microscopy, Auger electron spectroscopy, transmission electron microscopy, current-voltage and quantum efficiency measurement to bring out the variation in the growth behavior and cell efficiency on substrates having varied physical properties.