Recovering of Silicon Wafers for Silicon Fine Particles Production

Silicon wafer, the semiconductor, is the main component of silicon-based solar cells which carries around sixty percent of the cell cost. Moreover, ready-to-use wafers need the most energyconsumed manufacturing compared to other materials. Therefore, silicon wafers should be reused as many times as possible. Researchers have proposed several etching methods to recover standalone silicon wafers from whole solar cells. Surprisingly, the recovered wafers have identical properties to the original wafers from the industry, which means that they can be reused just like bulk silicon. Here, we demonstrate the chemical etching method to extract silicon and crush them into fine particles for further applications. We divided our work into two sections, (1) the silicon etching and (2) the ball milling (Fig. 1). In the 1st section, we used 6M HNO3 at 160oC for 5 min to remove the cell electrodes, then 85% H3PO4 for 15 min at 70°C to remove the anti-reflection coating and p-n junction, and finally 10M NaOH at 70oC for 5 min to clean all the remaining impurities, followed by ultrasonication in DI water for 10 mins. From that, the bulk wafers were ball-milled using a Fritsch Planetary miller with a 250 ml stainless-still vial and 5 mm balls at 400 rpm for 1 h (with a 10:1 ball-to-powder ratio) under ambient atmosphere and room temperature. The powder was then cleaned using acid treatment to remove the silicon oxide. As a result, fine silicon particles with an average size of not more than 120 nm were obtained with oxygen concentrations of 7.65% and 2.4% before and after acid treatment, respectively.