Potassium Cyanate Stabilizes Lattice and Promotes Preferred Orientation for 1.67‐eV Wide‐Bandgap Perovskite and Perovskite/Silicon Tandems

Wide-bandgap (WBG) perovskite solar cells are crucial for efficient perovskite/silicon tandem solar cells (PSTSCs). However, they often suffer from uncontrolled crystallization, phase instability, and non-radiative recombination losses due to crystallographic defects. Here, we report a facile strategy of regulating perovskite crystallization and passivating uncoordinated lead ions and halide vacancies by adding potassium cyanate (KOCN) into the perovskite precursor, which incorporates into the perovskite lattice to thereby suppressing non-radiative recombination. Moreover, KOCN modulates nucleation to promote a (110) orientation and releases strain. Consequently, KOCN-based 1.67 eV-WBG perovskite devices yield a champion efficiency of 23.60% with an impressive open-circuit voltage of 1.263 V and fill factor of 84.39%, enabling a 31.10% efficiency in two-terminal PSTSCs. After 1600 h of aging in the glovebox, the KOCN-doped device retains over 98% of its initial efficiency.