Direct Electrodeposition of Crystalline Silicon at Low Temperatures

Abstract

An electrochemical liquid-liquid-solid (ec-LLS) process that yields crystalline silicon at low temperature (80 °C) without any physical or chemical templating agent has been demonstrated. Electroreduction of dissolved SiCl(4) in propylene carbonate using a liquid gallium [Ga(l)] pool as the working electrode consistently yielded crystalline Si. X-ray diffraction and electron diffraction data separately indicated that the as-deposited materials were crystalline with the expected patterns for a diamond cubic crystal structure. Scanning and transmission electron microscopies further revealed the as-deposited materials (i.e., with no annealing) to be faceted nanocrystals with diameters in excess of 500 nm. Energy-dispersive X-ray spectra further showed no evidence of any other species within the electrodeposited crystalline Si. Raman spectra separately showed that the electrodeposited films on the Ga(l) electrodes were not composed of amorphous carbon from solvent decomposition. The cumulative data support two primary contentions. First, a liquid-metal electrode can serve simultaneously as both a source of electrons for the heterogeneous reduction of dissolved Si precursor in the electrolyte (i.e., a conventional electrode) and a separate phase (i.e., a solvent) that promotes Si crystal growth. Second, ec-LLS is a process that can be exploited for direct production of crystalline Si at much lower temperatures than ever reported previously. The further prospect of ec-LLS as an electrochemical and non-energy-intensive route for preparing crystalline Si is discussed.

Electrodeposition of Crystalline Gallium‐Doped Germanium and SixGe1−x from an Ionic Liquid at Room Temperature

“…[14] Applying a large negative potential should therefore assist in the formation of crystalline Si x Ge 1Àx , together with amorphous Si. Figure 6 shows the morphology of electrodeposited Si x Ge 1Àx .…”

“…[13] The same technique was also used to deposit silicon at 80 8C in gallium. [14] Our group has extensively investigated the electrodeposition of Ge and of Si x Ge 1Àx from ionic liquids that led to the formation of amorphous thin films. [15][16][17][18] Germanium electrodeposition was studied by in situ STM and STS.…”

Raman Spectroscopy Characterization of Dissolved Polysilicon Byproduct SiCl4 in Ionic Liquids

“…Abedin et al [12] reported the initial nanoscale electrodeposition of silicon on the room-temperature IL 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide saturated with SiCl 4 . Gu et al [13] indicated the presence of crystalline silicon at low temperature in an electrochemical liquid-liquid-solid process, wherein SiCl 4 was dissolved in an electrolyte system. Zhang et al [14] reported an efficient method to prepare crystalline Si from SiCl 4 at a low temperature of 100°C with IL [N4441]TFSI as the electrolyte.…”

Some Issues in Liquid Metals Research

“…Despite the rich variety of issues discussed in the ten papers published in this Special Issue, there is still a wealth of issues that deserve at least a brief comment in this Introduction. The study of liquid metals under microgravity conditions is throwing light on several key aspects of solidification [12,13]. The use of liquid-metal solutions to produce greener crystalline silicon is expected to provide a practical way to produce this old but still-essential material [14].…”