Sequentially deposited organic photovoltaics via self-solvent vapor annealing

Morphological control is recognized as a pivotal factor in developing high-performing solution-processed organic photovoltaics (OPVs). The essence of achieving optimal morphology in a sequentially deposited active layer lies in the precise modulation of the micro-morphology of the donor phase, encompassing molecular arrangement, orientation, and crystalline structure. The micro-morphology of the polymer donor layer plays a significant role in determining the vertical composition distribution and the adequacy of the donor/acceptor (D/A) interfaces. In this work, self-solvent vapor annealing (S-SVA) is employed to meticulously engineer the π-π stacking and crystalline domains of polymer donor PM6. This is accomplished by precisely adjusting the evaporation kinetics of the self-solvent and leveraging the swelling effect induced by residual self-solvents, thereby enhancing the self-assembly of PM6 molecules. The resultant improvements in π-π stacking and coherence length have led to efficient charge transport. These refinements have translated into a power conversion efficiency of 18.2%, accompanied by an open-circuit voltage of 0.886 V, a short-circuit current density of 25.9 mA cm⁻², and a fill factor of 79.4%. The straightforward yet impactful method not only enhances film crystallinity and device performance but also holds broad application potential.