Abstract: To enhance the device-performance and long-term stability of printable mesoscopic perovskite solar cells (MPSCs), an anion-cation synergistic strategy is proposed to introduce the ionic liquid additive 1-ethyl-3-methylimidazolium acetate (EMIMAC) into the perovskite active layer and use it for the preparation of efficient and stable MPSCs. The experimental results indicate that the imidazole (EMIM⁺) cation enables ionic defect passivation (e.g., Pb²⁺ and PbI₃^-) through the coordination effect, which is believed to be beneficial for perovskite crystallization. On the other hand, the acetate (AC^-) anion tends to coordinate with TiO₂ to passivate the oxygen vacancy defects on the TiO₂ surface for improved interfacial contact at the TiO₂/perovskite interface. As a result, the synergistic effects of the EMIM⁺ cation and AC^- anion in the EMIMAC achieves better perovskite crystallinity, more efficient charge transport, and lower nonradiative recombination. The power conversion efficiency (PCE) of the MPSCs increased from 13.83% to 15.48%, accompanied by a negligible hysteresis. Furthermore, the unencapsulated MPSCs exhibited excellent long-term stability by maintaining 90% of the initial PCE after exposure in air (RH=50±5%) for 60 days. The experimental results indicate that the ionic liquid additive EMIMAC can effectively enhance the PCE and stability of the device, providing an effective strategy for further improving the device-performance.