Upcycling Photovoltaic Silicon Waste into Si@MgO Fillers via Magnesiothermic Reduction for Thermally Conductive and Electrically Insulating Epoxy Composites

The rapid accumulation of end-of-life (EoL) solar cells necessitates economically viable, high-value upcycling strategies rather than conventional, high-cost recycling methods. High-purity silicon (Si) recovered from photovoltaic waste is a highly promising thermally conductive filler for advanced thermal management applications. However, its inherent semiconducting properties limit its applicability in electrically insulating systems required to prevent short circuits in highly integrated electronic devices. Furthermore, the silica (SiO₂) layer present on the Si surface exhibits relatively low thermal conductivity, which may impede efficient interfacial heat transfer.

To overcome these limitations, this study utilizes magnesiothermic reduction (MgTR) to modify the surface oxide layer of recovered Si and introduce Mg-containing oxide species onto the Si surface. Compared with SiO₂, MgO possesses higher intrinsic thermal conductivity while providing excellent electrical insulating properties. The recovered Si powders were subjected to MgTR at 700 °C for 2 h under an Ar atmosphere with varying Mg contents, and the resulting Si@MgO fillers were incorporated into an epoxy matrix. SEM-EDS analysis confirmed the presence of Mg and O on the surface of the MgTR-treated Si particles. At a filler loading of 40 vol%, the epoxy composite containing MgTR-treated Si exhibited a thermal conductivity of 1.08 W m⁻¹ K⁻¹, corresponding to a 22.7% enhancement compared with the non-MgTR Si/epoxy composite (0.88 W m⁻¹ K⁻¹). These results demonstrate the potential of MgTR-treated Si@MgO fillers for thermally conductive and electrically insulating polymer composites and provide a promising pathway for converting photovoltaic Si waste into high-value materials for electronic thermal management applications.