Room Temperature, Aqueous Deposition of Si Thin Films

We report combined galvanic and electroless deposition of Si onto Al alloys from 10 mM HF and 20 mM Na₂SiF₆ in 80 wt% formic acid.  Exposed Al acts as a reducing agent for Si deposition, but Al alone produces only nanoporous Si deposits.  Several low pH reducing agents were tested, but only formic acid allows deposition of compact Si thin films, which grow to 7-10 µm thickness after 30 hr.  These Si films contain significant Cu and Al contamination, both arising from the Al alloy substrate.  Compact Ge films can also be deposited from similar solutions.  Possible methods for obtaining photovoltaic grade thin film Si and Ge will be discussed.  Studies by voltammetry, electrochemical impedance spectroscopy (EIS), and spectroscopic ellipsomettry will also be discussed.