Synergistic Regulation of Ionic Defects Enabled by NdCl3 for Efficient and Stable Wide-Bandgap Perovskite Solar Cells.

Wide-bandgap mixed-halide perovskites are attractive top-cell absorbers for tandem photovoltaics owing to their high-voltage potential and complementary spectral response. However, ionic defects generated during solution processing promote nonradiative recombination, ion migration, etc. Here, NdCl3 is introduced into Cs0.17FA0.83PbI1.8Br1.2 perovskites to synergistically regulate ionic defects. Structural analyses suggest that Nd3+ preferentially incorporates into interstitial sites, where its strong electrostatic interaction with neighboring halide ions may contribute to restricting their migration. The reduced defect density observed upon NdCl3 modification points to effective defect passivation as a primary outcome. Meanwhile, Cl- compensates for halide vacancies, improves the local coordination environment, and suppresses trap-assisted nonradiative recombination. This synergistic regulation promotes grain growth, reduces defect density, facilitates carrier transport, and improves interfacial energy-level alignment. Consequently, the NdCl3-modified device achieves the highest power conversion efficiency of 19.87%. Moreover, the unencapsulated device retains 92.5% of its initial efficiency after 1680 h of ambient shelf storage (~25 °C, ~20% RH). These results demonstrate that the cooperative regulation of cation-associated ion migration and anion vacancies provides an effective route toward efficient and stable wide-bandgap perovskite photovoltaics.