Multifunctional Spacer in 2D/3D Wide‐Bandgap Perovskite for Monolithic Perovskite/Silicon Tandem Solar Cells

To maximize the power conversion efficiency (PCE) and stability of perovskite/silicon tandem solar cells (TSCs), high‐performance and stable perovskite top cells with wide‐bandgaps are required. A 2D/3D wide‐bandgap perovskite with a bandgap of 1.69 eV using 1H‐1,2,4‐triazole‐1‐carboximidamide (1‐TzFACl) as a spacer is developed. The 2D/3D wide‐bandgap perovskite shows better film quality, enhanced crystallinity, suppressed nonradiative recombination, and significantly improved phase stability. Its initial PCE (21.58%) remains above 87% after 1560 h of continuous illumination due to the insertion of Cl − in the perovskite lattice. A monolithic two‐terminal perovskite/silicon TSC achieves a PCE of 25.66% with high light stability. This work provides an ingenious strategy to restrain the phase segregation in wide‐bandgap perovskites, leading to effective and stable perovskite/silicon TSCs.