Catalyst-mediated doping in electrochemical growth of solar silicon

Abstract

The direct electrochemical reduction of silicon dioxide in molten CaCl2 has been investigated as a promising candidate for alternative production process of solar silicon. Herein, we study a catalyst-mediated doping, which is carried out by introducing dopant precursors like Al2O3, In2O3, and Sb2O3 into the molten CaCl2 during the electrochemical growth of silicon on Ag catalyst. The photoelectrochemical measurement demonstrates controllable p-type or n-type doping, and the photoresponse of doped silicon reaches 1.1 +/- 0.4 mA/cm(2) under 100 mW/cm(2) irradiation. Doping densities, estimated from two-point micro-probe measurements and Mott-Schottky plot analyses range from 10(15) to 10(16)/cm(3). Dopant is incorporated through Si-Ag catalyst droplet, which is supported by a high dopant content in Ag catalyst revealed by the elemental mapping of secondary ion mass spectroscopy. The catalyst-mediated doping mechanism is proposed to elucidate the doping level. The liquid droplet is presumed to be under local equilibrium along with significant loss of the dopant from it whereby the doping level becomes a function of the segregation coefficient and the rate constant of the electrochemical reaction. (C) 2020 Elsevier Ltd. All rights reserved.