Crystallization-driven effect enables organic solar cells with efficiency exceeding 19.4 %

• The highly crystalline N3 as crystallization driver increases the aggregation and crystallization rate of the acceptor, which enables the active layer to achieve the more ordered molecular arrangement, more obvious horizontal and vertical phase separation. • The addition of N3 effectively enhances the light capture ability of the active layer due the third component has better crystallinity and more ordered molecular arrangement. • This study indicates that the crystallization-driven effect of the ternary strategy is effective mechanism to improve performance of OSCs, which can provide a simple approach for selecting the third component. The ternary strategy is a key method to improve the performance of organic solar cells (OSCs). In this work, the highly crystalline small molecules acceptor N3 as the third component is introduced into a host system with polymer D18 as donor and the small molecules L8-BO as acceptor to construct highly efficient ternary OSCs. The highly crystalline N3 as the core seed crystal increases the aggregation and crystallization rates of the acceptor, which plays a role in crystallization-driven. This crystallization-driven effect enables the active layer to achieve the more ordered molecular arrangement, higher crystallinity, more obvious horizontal and vertical phase separation. After introducing the highly crystalline N3 into the D18: L8-BO system, the power conversion efficiency (PCE) of OSCs is increased from 18.13 % to 19.45 % accompanied by greater efficiencies of photon utilization, exciton dissociation, carrier transport and collection. This study indicates that the crystallization-driven effect of the ternary strategy is an effective mechanism for optimizing the morphology of the active layer, which can provide a simple approach for selecting the third component.