Perovskite solar cells (PSCs) have been developed rapidly recently and regarded as one of the most promising solar cells. It is still a challenge to fabricate PSCs with long-time stability. The main threat to the long-time stability of PSCs is the water molecules in air that can decompose the perovskite film. It is reported that blocking the contact between moisture and perovskite is an effective way to mitigate the decomposition of perovskite and stabilize the performance of the solar cells. So in this study, we improved the moisture resistance of the hole transport layer (HTL) by using hydrophobic additive, 2,2',7,7'-tetrakis(N,N-di-p-methoxy phenyl amine)-9,9'-spiro bifluorenedi[bis-(trifluoromethanesulfonyl) imide] (Spiro-(TFSI)(2)), to substitute the lithium bis(trifluoromethylsulphonyl)imide (Li-TFSI) with hygroscopic nature. Pinholes in the HTL also have been eliminated dramatically after the Spiro-(TFSI)(2) has been introduced into the HTL, which contributes to the further enhancement of the moisture resistance. The champion solar cell based on the Spiro-(TFSI)(2) with a power conversion efficiency (PCE) of 19.1% has been obtained, and the results demonstrate that the performance stability has been improved dramatically via introducing the hydrophobic additive into the HTL. This work has provided an effective method to improve the performance stability of PSCs. (C) 2018 Elsevier Ltd. All rights reserved.