Dual passivation effects of ionic liquids enable efficient and stable perovskite solar cells

In recent years, perovskite solar cells (PSCs) have been attracting more and more attention. Although perovskite materials have high defect tolerance, defects remain the main factor that seriously affects the efficiency and stability of PSCs. Herein, the ionic liquid of 1-butyl, 3-methylimidazolium acetate ([BMIM][ACO]) was introduced into the SnO₂/perovskite interface for the first time. Thanks to the dipoles formed by ILs spontaneously, the work function of SnO₂ was reduced and the transport ability of carriers was improved as well. Moreover, the Lewis acidity and lone pair electrons of [BMIM][ACO] contribute to the passivation of I^- defects, Pb²⁺ defects, or Pb-I anti site defects. In addition, the presence of dipoles will repel the approach of photogenerated holes and the reverse transport of electrons, reducing the recombination of defect sites through field-effect passivation. The solar cell with efficiency of 19.43% was obtained under such a dual passivation effect, and the best device maintained 75.21% of the initial efficiency after 80 h of continuous illumination.