Boosting the Efficiency of 1.84 eV Wide-Bandgap Perovskites Photovoltaics Beyond 19% via Yb³⁺ Engineering

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 Yb³⁺ 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, Yb³⁺ 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).