In recent years, although the power conversion efficiency (PCE) of thermally stable all-inorganic CsPbI₃ perovskite solar cells (PSCs) had shown a great progress, the most reported CsPbI₃ PSCs suffered from the large open-circuit voltage (V_oc) loss, which is related to severe nonradiative recombination and a mismatch in energy level at the transport layer/perovskite interface. In this work, europium acetate (EuAc₃) as a multifunction interface material is chosen to modify the TiO₂/perovskite interface, the crystal quality of CsPbI₃ perovskite films is improved, and both bulk and interfacial defects are reduced effectively. Meanwhile, the energy levels arrangement between TiO₂ and CsPbI₃ perovskites is also optimized, corresponding the raised built-in electric field afford a strength force to accelerate the transport and extraction of charge carriers from CsPbI₃ perovskites to TiO₂. As a result, the performance of CsPbI₃ PSCs is largely enhanced with the PCE of 16.76%. When an Ag electrode was replaced by Au, the PCE further improves to 17.92%, which is the highest for CsPbI₃ PSCs with P3HT as the HTL ever reported. Besides, the CsPbI₃ PSC with the EuAc₃ modification layer maintains 84% of the initial PCE under continuous UV irradiation for 250 h in a nitrogen filled glovebox, being obviously higher than the control devices with only 40% of the initial PCE after UV irradiation for 100 h in the same environment.