Inverted planar perovskite solar cells (PSCs) with poly(N,N?-bis(4-butylphenyl)-N,N?-bis(phenyl)benzidine) (PTPD) layer as hole-transporting layer (HTL) exhibit high power conversion efficiencies (PCEs) over 20%. However, the influence of PTPD?s molecular weight (Mw) on the performance of PSCs has not been reported yet. Herein, we employ PTPD with various molecular weights as HTL to fabricate highly efficient inverted planar PSCs. Our results show that PTPD with 75 kDa possesses superior conductivity, which can quicken the charge carrier extraction from perovskite to HTL. In addition, the MAPbI3 perovskite film atop the 75-kDa PTPD is smoother with higher crystallinity and lower defect density. As a result, inverted planar PSCs with 75-kDa PTPD as HTL deliver a highest PCE of 19.24%. Our work provides a beneficial reference for future preparation of stable and highly efficient inverted PSCs with polymer HTL.