Through-glass vias (TGVs) have been extensively researched due to the unique properties of glass, including low dielectric constant, high transparency, high mechanical, thermal and chemical resistance, and low cost. The TGVs are typically filled with Cu by electrodeposition to make electrical connections in high-performance electronics with 3D integration. The Cu electrodeposition process employed to fill the through-holes is similar to the one used for printed circuit boards (PCBs), and defect-free Cu can be achieved with a butterfly filling mechanism. This study introduces the defect-free Cu filling of TGVs using polyvinylpyrrolidone (PVP) as a leveler. The effects of PVP molecular weight on the formation of suppression layers on the Cu surface was examined by electrochemical analyses. It was found that the smaller PVP (10,000 g/mol) was beneficial, forming a more compact suppression layer. In contrast, the layer of larger PVPs (360,000 g/mol) contained a large number of defects where the accelerator could adsorb, resulting in conformal electrodeposition. As a result, the PVP with a molecular weight of 10,000 g/ mol led to defect-free butterfly filling at TGVs with increasing the filling performance by 20% compared to the larger PVP.