Direct Electrodeposition
of Crystalline Silicon at
Low Temperatures
- Publication date
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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<sub>4</sub> in propylene carbonate using a liquid
gallium [Ga(<i>l</i>)] 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(<i>l</i>) 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 <i>both</i> a source of electrons for
the heterogeneous reduction of dissolved Si precursor in the electrolyte
(i.e., a conventional electrode) <i>and</i> 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