Inducing crystal-oriented growth while inhibiting grain boundary migration with multifunctional ionic liquid for high-efficiency perovskite solar cells

The uncoordinated Pb 2+ and X - vacancy defects caused by the uncontrollable crystallization process are detrimental to the efficiency and stability of perovskite solar cells (PSCs). Herein, a multifunctional ionic liquid 1-butyl-3-methylimidazolium hexafluoroan (BMIMSbF 6 ) is introduced into perovskite to form an intermediate phase to induce crystal-oriented growth and passivate intrinsic defects. The results demonstrate that PbI 2 ·BMIMSbF 6 intermediate phase can delay the crystallization rate through molecular exchange and induce the crystal-oriented growth of perovskites. Moreover, by passivating uncoordinated Pb 2+ and X - vacancy defects, BMIMSbF 6 promotes the grain coarsening of perovskite and inhibits the grain boundary migration with an Urbach energy decreased by 10 meV. As a result, the PSCs with the BMIMSbF 6 additive achieves a champion power conversion efficiency (PCE) of 22.03% and improved long-term stability. In addition to comprehensively controlling the growth of perovskite, the chemically stable BMIMSbF 6 could prevent water infiltration to protect the perovskite and enhance its humidity stability. Thus, the PSCs with BMIMSbF 6 additive maintains 85% of its initial PCE after aging at 45% relative humidity for 500 h. This work highlights the multifunctional roles of BMIMSbF 6 to induce crystal-oriented growth, passivate intrinsic defects, and enhance humidity stability to form efficient and stable PSCs.