Dual-donor organic solar cells with 19.13% efficiency through optimized active layer crystallization behavior

D18:D18-Cl:L8-BO ternary organic solar cells (TSCs) with dual-donor are fabricated, and the highest power conversion efficiency (PCE) of 19.13% is achieved. The open circuit voltage of D18:D18-Cl:L8-BO TSCs is 0.915 V, the short circuit current density is 26.22 mA cm−2, and the fill-factor is 79.75%. D18 and D18-Cl form alloys in ternary films due to their similar chemical structures. The D18-Cl acts as a morphology modulator, enhancing the crystallization behavior of the active layer besides shortening the π-π and intermolecular stacking distances and augmenting the crystal coherence lengths. Moreover, adding D18-Cl can make the morphology of the active layer smoother and form a nanofiber structure. These factors collectively promoted charge extraction, transport, and collection. Furthermore, D18:D18-Cl:L8-BO TSCs exhibit excellent long-term stability, maintaining over 84% of the initials PCE after stored in N2-filled glove box for 4000 h. The work shows that it is feasible to prepare TSCs with high PCE and high stability using dual-donor with similar molecular structure.