Perovskite/Si double-junction (2J) tandem solar cells are attracting interest due to their 
rapidly increasing efficiency. Their certified record efficiency (34.9%, as of Dec. 1st, 2025) 
has surpassed the theoretical limit efficiency of single-junction (1J) solar cells. In this 
presentation, research progresses in the perovskite-based tandems done in our laboratory will 
be briefly introduced, especially focusing on strategies to achieve record-high efficiencies 
and good stability.[1-5] Recent works for utilizing commercial bottom cells such as PERC Si 
and CIGS will also be discussed.[6,7]