Selenocyanate Driven Organic Cations Homogenization in Wide‐Bandgap Perovskite

ABSTRACT

Achieving both high efficiency and long‐term stability in wide‐bandgap formamidinium ((FA ⁺ )‐based perovskite solar cells remains challenging. This difficulty primarily arises from FA ⁺ vacancy formation and halide ion migration, which induce ionic disorder and structural degradation. These coupled instabilities compromise lattice integrity, disrupt carrier dynamics, and accelerate device decay. Here, we introduce selenocyanate (SeCN ⁻ ) pseudohalide anions into wide bandgap (1.66 eV) FA‐based perovskites to simultaneously stabilize the lattice and suppress ion migration. Leveraging its lattice compatibility and robust hydrogen bonding with FA ⁺ , the formation energy of FA ⁺ vacancies is raised, thereby increasing the migration barrier for I ⁻ , thereby mitigating ionic heterogeneity. Consequently, SeCN ⁻ ‐doped films exhibit uniform FA distributions both laterally and vertically, reduced defect densities, and a more robust lattice network. These microscopic improvements translate into substantial device‐level benefits: single‐junction wide‐bandgap solar cells deliver efficiencies exceeding 24%, while monolithic perovskite/silicon tandem devices achieve over 32% efficiency and retain more than 90% of their initial performance after 1000 h of continuous operation. This work establishes anion‐site engineering with pseudohalides as a promising strategy to homogenize cation distributions, stabilize lattice structures, and suppress ion migration.