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The limited exciton lifetime (τ, generally <1 ns) leads to short exciton diffusion length (LD) of organic semiconductors, which is the bottleneck issue impeding the further improvement of power conversion efficiencies (PCEs) for organic solar cells (OSCs). However, efficient strategies to prolong intrinsic τ are rare and vague. Herein, we propose a facile method to efficiently reduce vibrational frequency of molecular skeleton and suppress exciton‐vibration coupling to decrease non‐radiative decay rate and thus prolong τ via deuterating nonfullerene acceptors. The τ remarkably increases from 0.90 ns (non‐deuterated L8‐BO) to 1.35 ns (deuterated L8‐BO‐D), which is the record for organic photovoltaic materials. Besides, the inhibited molecular vibration improves molecular planarity of L8‐BO‐D for enhanced exciton diffusion coefficient. Consequently, the LD increases from 7.9 nm (L8‐BO) to 10.7 nm (L8‐BO‐D). The prolonged LD of L8‐BO‐D enables PM6 : L8‐BO‐D‐based bulk heterojunction OSCs to acquire higher PCEs of 18.5 % with more efficient exciton dissociation and weaker charge carrier recombination than PM6 : L8‐BO‐based counterparts. Moreover, benefiting from the prolonged LD, D18/L8‐BO‐D‐based pseudo‐planar heterojunction OSCs achieve an impressive PCE of 19.3 %, which is among the highest values. This work provides an efficient strategy to increase the τ and thus LD of organic semiconductors, boosting PCEs of OSCs. [ABSTRACT FROM AUTHOR]