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.