Initial Stage of Si Electrodeposition Process in Ionic Liquids

Abstract

Si thin films are key material for electronic/energy devices such as photovoltaic cells and battery electrodes, as well as various MEMS devices. For their fabrication process, electrochemical approaches attract attention featuring high productivity and precise controllability to form micro/nano structures to wide surfaces. Since Si has very negative redox potential, non-aqueous electrolytes with molten salts, ionic liquids (ILs), or organic solvents are required. We have applied the ILs such as trimethylhexyl ammonium (TMHA+) bis-trifluorosulfonyl imide (TFSI-) and investigated their deposition process focusing upon the initial stage. The analysis using electrochemical quartz crystal microbalance (EQCM) [1] suggested that the reaction of the source of Si in the electrolyte, SiCl4, proceeded via Si (III) and Si(II) intermediate species. From the results of X-ray reflection (XRR) analysis and density functional theory calculation [2], it was indicated that the SiCl4 species adsorped onto the surface initially formed multimer, and this “precursor” was subsequently transformed into Si layers.The authors would like to thank Dr. J. Komadina, Mr. M. Nishida, and Mr. T. Fujimura for their experimental help and valuable discussion. This study was financially supported in part by the Japan Science and Technology Agency (JST) CREST program.[1] Y. Tsuyuki, A. Pham, J. Komadina, Y. Fukunaka, T. Homma, Electrochim. Acta, 183, 49 (2015).[2] Y. Tsuyuki, T. Fujimura, M. Kunimoto, Y. Fukunaka, P. Pianetta, T. Homma, J. Electrochem. Soc., 164, D994 (2017).