Dual Potassium Salts Modulation of Perovskite Quality for Efficient Perovskite Photovoltaics

ABSTRACT Solution processing of mixed‐halide perovskites inevitably leads to inferior crystallinity and introduces undesired defects, arising from inhomogeneous ion mixing in the precursor solution or rapid solvent evaporation and uncontrollable nucleation/growth, thereby impairing both the power conversion efficiency (PCE) and long‐term stability of perovskite solar cells (PSCs). Here, we report a synergistic dual‐additive strategy utilizing potassium thiocyanate (KSCN) and potassium iodide (KI) to tailor the solution chemistry of perovskite precursors. The synergistic incorporation of thiocyanate ion (SCN − ), potassium ion (K + ), and iodide ion (I − ) optimizes the crystallization process through kinetics modulation, achieving multi‐site passivation via ionic interactions, thereby enabling high‐quality perovskite films and enhancing the optoelectronic performance of the devices. Consequently, we demonstrate a champion PCE of 26.09% for formamidinium‐cesium‐based single‐junction PSC with a high open‐circuit voltage ( V OC ) of 1.205 V, along with maintaining 90.8% of its initial efficiency after 500 h of continuous operation at 65°C under 1 sun illumination in ambient air. Crucially, this strategy is fully compatible with the fabrication of all‐perovskite tandem solar cells, empowering a high PCE of 28.76%.