Localized Potential Regulation on Polymer Donor Backbone Suppresses Energetic Disorder for Efficient, Stable and Scalable Organic Solar Cells

High energetic disorder and short exciton diffusion lengths in low‐crystallinity polymer donors ( P D s) critically limit exciton dissociation, charge transport, efficiency, stability, and scalability of organic solar cells (OSCs). Here we report a localized potential regulation strategy to intrinsically suppress energetic disorder of P D through precise backbone engineering. By introducing a strongly electron‐deficient unit into the structurally disordered backbone of the DP1, we developed a P D DP10 that exhibits enhanced backbone rigidity, optimized local electronic polarization, and favorable miscibility with the acceptor L8‐BO. These features synergistically reduce the exciton binding energy and suppress exciton–phonon coupling, thereby extending the exciton diffusion length from 15.5 to 19.9 nm. Consequently, DP10 enables balanced, trap‐tolerant charge transport and reduced non‐radiative recombination in devices. The DP10:L8‐BO binary system achieves a device efficiency of 19.51%, together with exceptional thermal stability and outstanding thickness‐tolerant performance. Additionally, a DP10:L8‐BO:BTP‐eC9 ternary device reaches an efficiency of 20.57% and a 15.1 cm 2 solar module delivers 17.20% efficiency, with impressive fill factors of 81.04% and 77.39%, respectively. This work establishes localized potential regulation as a powerful molecular design principle of P D s for simultaneously achieving high efficiency, thermal stability, and processing robustness in next‐generation OSCs.