Tautomeric Dual‐Site Passivation for Carbon‐Based Printable Mesoscopic Perovskite Solar Cells

Abstract Although ionic conjugated passivation systems, such as ionic liquids (ILs), have been used to passivate perovskite in carbon‐based printable mesoscopic perovskite solar cells (FP‐PSCs), their tautomerism process and synergistic effect of multifunctional groups have not yet caused enough attention. In this work, a series of novel ILs including 1‐allyl‐3‐methylimidazole tetrafluoroborate ([AMIm]BF 4 ) and 1‐benzyl‐3‐methylimidazole tetrafluoroborate ([BzMIm]BF 4 ) used as passivants for FP‐PSCs are reported. Combining Fourier transform infrared spectroscopy, X‐ray photoelectron spectroscopy (XPS), and density functional theory (DFT) calculation, it is found that one of its tautomers (positive ion at the near end N atom of conjugated side chain) plays a key role on dual‐site simultaneous passivation. As the conjugation degree of side chain increases from allyl to benzyl, it not only effectively inhibits the non‐radiative charge recombination, but also reduces the passivation adsorption energy and increases the charge transfer rate. A high efficiency of 16.87% has been achieved with a high FF (>0.7), a J sc of 23.88 mA cm –2 value and V oc value up to 1.0 V, by using the “tautomeric dual‐site passivation” strategy.