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

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 (T80:769 h) under continuous light-soaking condition.