Rational Design of Functional Additives for Synergistic Photovoltaic and Mechanical Enhancement in Organic Photovoltaic Cells

Simultaneously achieving high photovoltaic efficiency and mechanical compliance remains a major challenge for stretchable organic photovoltaic cells (OPVs). Here, we present a rational additive‐engineering strategy based on quinoxaline‐thymine small molecules (Qx‐ThyX) with tunable alkyl chain lengths to synergistically regulate the optoelectronic and mechanical properties of OPV active layers. Incorporation of these functional additives into PM6:BTP‐eC9 blends introduces reversible hydrogen–bonding interactions and flexible segments, enabling precise modulation of donor–acceptor morphology and crystallization behavior. As a result, both photovoltaic performance and film stretchability are concurrently improved. An optimal device with 3 wt% Qx‐Thy10 achieves an enhanced power conversion efficiency, while higher additive loadings significantly increase crack‐onset strain and reduce elastic modulus, indicating pronounced mechanical softening. Systematic studies reveal that extending the alkyl chain length further enhances mechanical compliance, whereas excessive additive incorporation compromises charge extraction. Fragment analysis uncovers a clear structure–property relationship, where the quinoxaline unit governs photovoltaic performance and the thymine‐alkyl segment dominates mechanical reinforcement. This work establishes an effective molecular design framework for high‐performance stretchable OPVs.