Structure stabilized with robust molecular cation N(CH3)4+ in high efficiency perovskite solar cells

Polarity and acid–base equilibrium of the A-site ions in organic-inorganic hybrid perovskites are the major origins of structure instability that limits the efficiency of perovskite solar cells (PSCs). It is effective to stabilize the structure of perovskite by partial replacement of A-site ions with larger radius and non-polar ions. Here, we fabricate tetramethylammonium ions N(CH3)4+ (TMA+) substituting perovskite, MA1-xTMAxPbI3, by partially replacing MA+ in MAPbI3 with large and rigid TMA+. Theoretical and experimental study demonstrates that the introduction of TMA+ cation in MA1-xTMAxPbI3 perovskite leads to a more stable crystal structure and reduces the defects state density in perovskite films. The PSCs based on MA1-xTMAxPbI3 (x = 0.15) films demonstrate a champion efficiency of 22.23% and an improved stability against air environment. This work highlights the significance of A-site ionic characteristics of perovskite structure and provides a new strategy in constructing high efficiency and stable hybrid PSCs.