N‐Heterocyclic Olefin Type Ionic Liquid with Innate Soft Lewis‐Base Character as an Effective Additive for Hybrid Quasi‐2D and 3D Perovskite Solar Cells

In optimizing perovskites with ionic liquid (IL), the comparative study on Lewis acid-base (LAB) and hydrogen-bonding (HB) interactions between IL and perovskite is lacking. Herein, methyl is substituted for hydrogen on 2-position of imidazolium ring of N-heterocyclic carbene (NHC) type IL IdH to weaken HB interactions, and the resulting N-heterocyclic olefin (NHO) type IL IdMe with softer Lewis base character is studied in both hybrid quasi-2D (Q-2D) and 3D perovskites. It is revealed that IdMe participates in constructing high-quality Q-2D perovskite (n = 4) and provides stronger passivation for 3D perovskite compared with IdH. Power conversion efficiency (PCE) of Q-2D PEA2 MA3 Pb4 I13 perovskite solar cells (PVSCs) is boosted to 17.68% from 14.03%. PCE and device stability of 3D PVSCs enhances simultaneously. Both theoretical simulations and experimental results show that LAB interactions between NHO and Pb2+ take the primary optimization effects on perovskite. The success of engineering LAB interactions also offers inspiration to develop novel ILs for high-performance PVSCs.