Organic–inorganic hybrid perovskites have attracted a lot of research attention because of their superior optoelectrical properties and great promise for commercialization. Yet, a large number of defects and trap states in perovskites resulted in high device energy loss and hindered their performance as active layers in optoelectronic devices, including solar cells. Here, we designed and synthesized a typical polymer zwitterion (PMPC) with side chains of phosphorylcholine (PC) through reversible addition–fragmentation chain transfer (RAFT) polymerization. This synthesis provides a platform to combine various functional groups (e.g., zwitterions, Lewis bases and carboxylic acid) in one polymer chain, affording a multifunctional polymer passivator, which shows the ability to suppress the non-radiative recombination in perovskites, to the benefit of decreasing the voltage loss (V_loss) and enhancing the build-in potential (V_bi) of the solar cell devices. The integration of PMPC into perovskite precursors improves the crystallization and passivates the defects of perovskite films, to alleviate the space charge limit and suppress the trap-assisted recombination process in solar cell devices. Finally, PMPC passivation improved the solar cell efficiency from 18.77% to 20.16% along with better device stability. This notable optimization of perovskite devices using the phosphorylcholine-based polymer zwitterion provides a straightforward molecular design strategy to achieve multifunctional materials for perovskite passivation.