Band Gap Matching for Minimized Recombination Loss in Efficient Perovskite/Organic Tandem Solar Cells ^†

Comprehensive Summary High quality light‐absorbing layers with matched band gaps of sub‐cells are crucial for achieving high power conversion efficiency (PCE) in the perovskite/organic tandem solar cells (PO‐TSCs). In this work, we systematically optimized the band gaps of wide‐bandgap perovskite layer (1.73–1.85 eV) and narrow‐bandgap organic active layer (1.34–1.38 eV). An asymmetric small‐molecule acceptor, namely SY2 (two F atoms and two Cl atoms), is introduced into the PM6:BTP‐eC9 blend to enhance the light absorption, form the fibril network morphology, and facilitate exciton dissociation and transport. By precisely integrating a 1.80 eV perovskite sub‐cell and a 1.34 eV ternary organic sub‐cell, we achieved a champion PCE of 25.47% for the PO‐TSCs based on the well‐matched short‐circuit current density. Besides, the optimized devices exhibited outstanding long‐term stability. Our findings highlight the importance of band gap matching between front and near sub‐cells in reducing recombination loss for high‐performance tandem solar cells.