Theoretical Analysis of Experimental Data of Sodium Diffusion in Oxidized Molybdenum Thin Films

Orlando Ayala, Benjamin Belfore, Tasnuva Ashrafee, John Akwari, Grace Rajan, Shankar Karki, Deewakar Poudel and Sylvain Marsillac
Additional contact information
Orlando Ayala: Department of Engineering Technology, Old Dominion University, Norfolk, VA 23529, USA
Benjamin Belfore: Virginia Institute of Photovoltaics, Old Dominion University, Norfolk, VA 23529, USA
Tasnuva Ashrafee: Virginia Institute of Photovoltaics, Old Dominion University, Norfolk, VA 23529, USA
John Akwari: Virginia Institute of Photovoltaics, Old Dominion University, Norfolk, VA 23529, USA
Grace Rajan: Virginia Institute of Photovoltaics, Old Dominion University, Norfolk, VA 23529, USA
Shankar Karki: Virginia Institute of Photovoltaics, Old Dominion University, Norfolk, VA 23529, USA
Deewakar Poudel: Virginia Institute of Photovoltaics, Old Dominion University, Norfolk, VA 23529, USA
Sylvain Marsillac: Virginia Institute of Photovoltaics, Old Dominion University, Norfolk, VA 23529, USA

Energies, 2021, vol. 14, issue 9, 1-20

Abstract: In this work, the diffusion process of sodium (Na) in molybdenum (Mo) thin films while it was deposited on soda lime glass (SLG) was studied. A small amount of oxygen was present in the chamber while the direct-current (DC) magnetron sputtering was used for the deposition. The substrate temperatures were varied to observe its effect. Such molybdenum films, with or without oxidations, are often used in thin film solar cells, either as back contact or as hole transport layers. Secondary ion mass spectrometry (SIMS) was used to quantify the concentration of the species. A grain diffusion mechanistic model incorporating the effect of grain and grain boundary geometrical shape and size was developed. The model was used to provide an in-depth theoretical analysis of the sodium diffusion in molybdenum thin films that lead to the measured SIMS data. It was observed that not only diffusion coefficients should be considered when analyzing diffusion processes in thin films but also the ratio of grain boundary size to grain size. Both depend on substrate temperature and directly affect the amount of diffused species in the film. The data were analyzed under the light of the film growth speed versus diffusion front speed, the effect of oxygen content, and the effect of substrate temperature on the overall diffusion process. The temperature inversely affects the ratio of grain boundary size and grain size and directly affects the diffusion coefficient, which leads to a preferable temperature at which the highest amount of alkali can be found in the film.

Keywords: modeling; thin films; diffusion; molybdenum (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2021
References: View complete reference list from CitEc
Citations: View citations in EconPapers (1)

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