With the development of material engineering, interface modification, and advanced device processing in past decades, the power conversion efficiency (PCE) of the state-of-the-art PSCs has already reached 12% at present. we designed a novel chlorinated polymer donor PBT4T-Cl, and the PSCs using PBT4T-Cl showed a high PCE of 11.18%, which is the highest PCE of chlorinated polymer-based PSCs and is also one of the highest PCEs of FBT-based PSCs reported to date. The results demonstrated chlorine substitution of the thiophene moiety could tune-finely the HOMO energy level of the corresponding polymer as well as the charge carrier mobility and the morphologies of the blend film, eventually improving its photovoltaic properties as a donor without requiring thermal annealing. The PBT4T-Cl-based devices also showed less additive dependency than the control devices did (non-Cl-based polymer). Analysis on the GIWAXS illustrated the strong crystallinity from the blend film, and AFM and TEM measurements both revealed an optimized morphology of the spin-coated PBT4T-Cl/PC71BM film without thermal annealing, all of which supported the PCE enhancement of chlorine-substituted polymer, and chlorine atoms attached to a suitable backbone would obviously promote the performance of polymer solar cells. Moreover, the chlorinated polymer-based PSCs exhibited favorable stability in the lifetime test compared with non-chlorinated analogs. Therefore, chlorination of the polymer donor is a feasible strategy to simultaneously increase the performance and stability of PSCs, eventually promoting the commercialization of PSCs.