Extraction and Analysis of Recovered Silver and Silicon from Laboratory Grade Waste Solar Cells

Abstract

In the present work, a new process is reported to recover metallic contacts and wafer from the crystalline silicon solar cell through chemical etching. 2 M KOH was used as an etching solution at temperatures 110 ± 1 °C and 85 ± 1 °C. During the process, metallic contacts were extracted, without breaking, in the form of fingers and foils along with the silicon wafer. The contacts and recovered wafer were characterized through Scanning Electron Microscopy, Energy Dispersive Spectroscopy, X-ray fluorescence spectroscopy, X-Ray Diffraction, Electrochemical Capacitance Voltage Analysis, Four Probe Measurement technique, and Ultraviolet absorption spectroscopy. It was found that the recovered wafer is of P-type with 100 orientation and has a bulk resistivity of ~1 Ω cm with a dopant density of 2× 10¹⁶ – 4.5 × 10¹⁶ atoms per cm³. The recovered wafer thickness was found to be etching temperature-dependent. High processing temperature (110 °C) deteriorated the wafer resulting in deep groove formation on the front surface and led to decrement in wafer thickness. No grooves were observed in the sample treated at a lower temperature (85 °C), and the thickness was also not reduced too much. The recovered contacts were mainly composed of silver. Lead present on the back contact was removed during the process resulting in the recovery of silver contacts with a purity of ~99%. UV absorption spectroscopy confirmed the removal of lead in the form of lead(II) complex ion. The etching process also led to the complete removal of the p-n junction from the solar cells.