AVS 51st International Symposium
    Thin Films Thursday Sessions
       Session TF-ThA

Paper TF-ThA1
Study of Molybdenum Back Contact Layer to Achieve Adherent and Efficient CIGS2 Absorber Thin-Film Solar Cells

Thursday, November 18, 2004, 2:00 pm, Room 303C

Session: Photovoltaic Thin Films
Presenter: A.A. Kadam, University of Central Florida
Authors: N.G. Dhere, Florida Solar Energy Center
A.A. Kadam, University of Central Florida
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Molybdenum is used as back contact layer in CuIn@sub 1-x@Ga@sub x@S2 (CIGS2) absorber thin film solar cells. Mo is sputter deposited using DC magnetron sputtering. Mo being refractory material develops stresses. It is essential to deposit stress-free and relatively inert Mo in order to achieve well adherent and highly efficient CIGS2 absorber thin film solar cells on stainless steel and glass substrates. Earlier studies have shown that films deposited at 300 W and 0.3 mT pressure develops compressive stress, while the films deposited at 200 W and 5 mT pressure develops tensile stress. Four experiments were carried out to achieve optimum deposition cycle to deposit stress free Mo. In first experiment two cycles of 200 W/5 mT were sandwiched between three cycles of 300 W/0.3 mT. In second experiment two cycles of compressive stress were sandwiched between three cycles of tensile stress. In third experiment two cycles each of compressive stress and tensile stress were deposited alternatively starting with compressive cycle and ending with tensile cycle. The fourth experiment was conducted in reverse order, starting with tensile and ending with compressive. All the depositions were carried out on 15 x 10 cm@super 2@ stainless steel substrates. 5 x 10 cm@super 2@ strip was cut and remaining 10 x 10 cm@super 2@ was deposited with metallic precursors copper-gallium and indium. Metallic precursors were sulfurized at 475°C for 20 minutes in a gas mixture of 4% H@sub 2@S/N@sub 2@. The presentation describes the XRD and SEM analysis to study the quality of films as a consequence of deposition cycle of Mo back contact layer. TEM analyses are also presented to study Mo/CIGS2 interface behavior. Small region of Mo films on remaining 5 x 10 cm@super 2@ strips were tested for adhesion by simple scotch tape test and remaining part was sulfurized at 475°C for 20 minutes to study the reactivity of Mo with H@sub 2@S at the operating temperature.