Decoupling Competing Roles of Energetic Disorder and Molecular Structural Order in Organic Photovoltaics

ABSTRACT Minimizing non‐radiative voltage loss remains a key challenge for organic solar cells (OSCs), yet the interplay between energetic disorder and molecular structural order is not well understood. By systematically varying polymer donors (PM6, PTzBI‐dF, D18‐Cl) blended with L8‐BO, we decouple these factors using temperature‐dependent open‐circuit voltage ( V _OC ) measurements. While a planar donor backbone (PTzBI‐dF) promotes molecular packing and raises the ideal V _OC limit ( V _{OC , ideal} ) extrapolated to 0 K, it simultaneously induces severe energetic disorder. Temperature‐dependent mobility analysis reveals significant Gaussian broadening parameters ( σ _HOMO = 98 meV; σ _LUMO = 89 meV) for PTzBI‐dF, leading to substantial non‐radiative losses and a low room‐temperature V _OC . Crucially, the detrimental impact of energetic disorder outweighs the benefits of structural order, particularly below 200 K, where carrier thermalization into disorder induced tail states enhances non radiative recombination. These findings identify energetic disorder as the primary bottleneck to V _OC and highlight the necessity of balancing molecular structural order with disorder suppression for next‐generation OSC development.