Bifunctional ionic liquid for enhancing efficiency and stability of carbon counter electrode-based MAPbI3 perovskites solar cells

•Acetate ion functionalized polar ionic liquid (IL), 1-allyl-3-methylimidazolium acetate (AMIMOAc), has firstly been used not only as an additive in MAPbI3 perovskite film but also as an interfacial modification layer between SnO2 and MAPbI3 in carbon counter electrode-based perovskite solar cells.•The appropriate content of IL can reduce the number of trap states in MAPbI3 perovskite film to inhibit non-radiative recombination and increase carrier lifetime, further improve the PCE to 15.16%.•The stability of the devices has been improved remarkably. The device with AMIMOAc IL has retained 93% of its initial PCE after storing for 500 h.