Dual‐Phase Regulation via a Volatile Morphology Director Enables Trap‐Suppressed Organic Solar Cells with 20.6% Efficiency

Abstract Immense trap densities arising from faint donor self‐assembly and excessive acceptor aggregation severely restrain power conversion efficiencies (PCEs) in organic solar cells. Yet, most studies focus solely on acceptor regulation, and synergistic co‐modulation of donor and acceptor phases for trap suppression has rarely been achieved. Here, 1,3‐dibromo‐5‐iodobenzene (DBI) as a volatile solid additive with multiple noncovalent interactions to concurrently optimize both phases is introduced. Using PM6:Y6 as representative, from systemic coarse‐grained molecular dynamic simulation, in‐situ synchronic and spectroscopy and transient optoelectronic characterizations, it is demonstrated that DBI can selectively bind with the fluorinated benzo[1,2‐b:4,5‐b′]dithiophene segments in PM6 backbone, which strengthens interchain interactions, enhances interchain packing density, and triggers the pre‐aggregation of PM6 in solution state. Moreover, this preferentially precipitation of PM6 matrix sterically mitigates the oversized Y6 aggregation, which yields well‐defined phase separation with appropriate domain sizes, which markedly substitute energetic disorder and trap density. As a result, the DBI treated devices yielded an elevated performance of 18.4% compared to 17.0% for reference devices. The generality of such strategy is also validated by PM6:L8‐BO:L8‐BO‐F ternary system, where adding an optimal amount of DBI achieves a champion PCE of 20.6% with a boosted operational stability (T 80 :769 h) under continuous light‐soaking condition.