Study of molybdenum back contact layer to achieve adherent and efficient CIGS2 absorber thin-film solar cells
Abbreviated Journal Title
J. Vac. Sci. Technol. A
Materials Science, Coatings & Films; Physics, Applied
Molybdenum is used as back contact layer in I-III-VI2 compound thin-film solar cells. Mo film was sputter deposited on 125-mm-diameter Si wafer having 100 orientation using dc magnetron sputtering. Films with similar parameters were also deposited on 2.5 cm x 10 cm soda-lime glass for studying the adhesion to the substrate and chemical reactivity of molybdenum with H2S gas at 475 degrees C for 20 min. Mo being refractory material develops stresses. It is essential to deposit stress-free and relatively inert Mo films in order to achieve well adherent and highly efficient CuIn1-xGaxS2 absorber thin film solar cells on flexible metallic foil and glass substrates. Earlier have shown that films deposited at sputtering power of 300 W and 0.3 x 10(-3) Torr working argon pressure develop compressive stress, while the films deposited at 200 W and 5 x 10(-3) Torr pressure develop tensile stress. Four sets of experiments were carried out to achieve optimum deposition cycle to deposit stress-free Mo. In the first experiment, Mo thickness of 138 nm was deposited at 300 W power and 0.3 x 10(-3) Torr pressure. In the second experiment Mo thickness of 127 nm was deposited at power of 200 W and pressure of 5 x 10(-3) Torr. Two more experiments were carried out by using alternate layers to reduce the overall stress. In a third experiment, two high power cycles were sandwiched between three low power cycles with total film thickness of 330 nm. In a fourth experiment two low power cycles were sandwiched between three high power cycles resulting in effective thickness of 315 nm. This article describes the wafer bending analysis for stress measurement, x-ray diffraction for crystal quality, scanning electron microscopy for surface morphology and Auger electron spectroscopy for the extent of sulfur diffusion in Mo layer. (c) 2005 American Vacuum Society.
Journal of Vacuum Science & Technology A
Article; Proceedings Paper
"Study of molybdenum back contact layer to achieve adherent and efficient CIGS2 absorber thin-film solar cells" (2005). Faculty Bibliography 2000s. 5319.