A novel ionic liquid, 3-(3-aminopropyl)-1-methylimidazolium hexafluorophosphate (APMimPF(6)), with high hydrophobic property was successfully applied as the functional monomer for the halide perovskite preparation. The new hydrophobic ionic liquid significantly facilitates the perovskite forming a 2-dimensional structure with good passivation, particularly at the grain boundaries because of the high hydrophobic character and large size of ionic liquid molecule. The perovskite solar cell fabricated with this new perovskite based on the hydrophobic ionic liquid was found possessing excellent properties: the maximum value of Jsc = 22.9 mAcm(-2), Voc = 1.05 V, and PCE = 17.3%. In addition, the perovskite solar cell also shows good long-term stability, which benefited from the protecting effect of the high hydrophobic ionic liquid. In a typical stability test, the cells stored under the conditions with a relative humidity of 57% for 40 days, the PCE was able to retain 98% of its initial value. Therefore, the present study demonstrated a significant protocol for the development of highly stable perovskite solar cells. (c) 2019 Elsevier Ltd. All rights reserved.