Energy level and the charge extraction/transportation ability of the hole transport layer (HTL) have significant impacts on the photovoltaic (PV) parameters of the perovskite solar cell (PSC) devices. A doping process has been one of the representative works to manage these characteristics, but the solution-blend doping, widely applied to the organic semiconductor HTL, has shown limited processability. In this work, we design a facile interfacial doping process for poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA) HTL in p-i-n structure PSC device. This approach provides superior optical and electrical properties to the PTAA layer, even with better processability, and its proper hydrophobicity is beneficial to forming pinhole-free perovskite even with superior crystallinity and reduced trap density. Moreover, the dipole layer localized at the interface with the perovskite enhance the built-in potential of device, improving its carrier transportation. As a result, this approach largely enhances the efficiency of the p-i-n PSC device from 18.06% (blend-doping) to 20.67% with superior stability preserving 94% of its initial efficiency after 500 h under ambient air.