Boosting the Efficiency of 1.84 eV Wide‐Bandgap Perovskites Photovoltaics Beyond 19% via Yb 3+ Engineering

Abstract Phase segregation remains one of the most critical challenges limiting the performance and long‐term operational stability of wide‐bandgap perovskite solar cells (PSCs). This issue is especially pronounced in 1.84 eV wide‐bandgap (WBG) perovskites, where severe halide phase segregation leads to compositional heterogeneity and accelerated device degradation. In this work, a comprehensive investigation of halide ion distribution across the surface and bottom interfaces of 1.84 eV perovskite films is conducted, revealing significant Br − /I − halide phase segregation that severely impairs device efficiency and stability. To address this, Ytterbium (III) trifluoromethanesulfonate (Yb(TFSI) 3 ) is introduced as a multifunctional additive in the perovskite precursor. The strong coordination between Yb 3+ ions and halide anions not only modulates the crystallization kinetics but also homogenizes the spatial distribution of Br‐rich and I‐rich domains, resulting in high‐quality perovskite films with reduced compositional heterogeneity. Furthermore, Yb 3+ significantly suppresses halide migration and ion exchange processes, thereby enhancing phase stability. Depth‐resolved characterizations, including grazing‐incidence wide‐angle X‐ray scattering, confirm improved crystallinity, structural uniformity, and suppressed phase segregation across the film depth. As a result, the champion device achieves an outstanding power conversion efficiency (PCE) of 19.06% and retains 85% of its initial efficiency after 1500 h in a nitrogen atmosphere (10% RH, 25 °C).