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

The uncoordinated Pb2+ 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 (BMIMSbF6) is introduced into perovskite to form an intermediate phase to induce crystal-oriented growth and passivate intrinsic defects. The results demonstrate that PbI2·BMIMSbF6 intermediate phase can delay the crystallization rate through molecular exchange and induce the crystal-oriented growth of perovskites. Moreover, by passivating uncoordinated Pb2+ and X- vacancy defects, BMIMSbF6 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 BMIMSbF6 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 BMIMSbF6 could prevent water infiltration to protect the perovskite and enhance its humidity stability. Thus, the PSCs with BMIMSbF6 additive maintains 85% of its initial PCE after aging at 45% relative humidity for 500 h. This work highlights the multifunctional roles of BMIMSbF6 to induce crystal-oriented growth, passivate intrinsic defects, and enhance humidity stability to form efficient and stable PSCs.