Ionic Site Competition Strategy Enhances Wide-Bandgap Perovskite Stability for Silicon-Based Tandem Photovoltaics

Stable wide-bandgap (WBG) perovskites are essential for realizing efficient monolithic perovskite-silicon tandem devices, yet their intrinsic instability due to halide segregation remains a major challenge. Here, we report an ionic site competitive strategy to stabilize WBG perovskites by simultaneously eliminating bulk defects and maintaining halide homogeneity. By tailoring precursor chemistry using multiple chloride (Cl) ion sources with distinct bond energies, Cl– ions are guided into either lattice or interstitial positions. Lattice-incorporated Cl– ions suppress intrinsic lattice defects and enhance halide mixing, while interstitial Cl– ions relieve lattice strain induced by mixed halide compositions. The resulting perovskites exhibit significantly suppressed halide segregation, reduced nonradiative recombination, and improved optoelectronic quality. Finally, the WBG perovskite solar cell yields an efficiency of 23.88%, while the two-terminal perovskite-silicon tandem device reaches 32.39% efficiency with good operational stability, retaining over 90% of its initial efficiency after a 1000 h continuous test.