Guest-Mediated Orthogonal Crystallization for Highly Efficient Organic Solar Cells

The multicomponent strategy is widely recognized as an effective approach for enhancing the performance of organic solar cells (OSCs). While guest components can bring multiple benefits, the ability to precisely regulate molecular crystallization, ensuring inertness toward one host component while directing the assembly of the other, remains highly impactful and challenging. Herein, we propose a guest-mediated orthogonal crystallization strategy in which the guest component achieves dual functionality: it directs the crystallization of the acceptor without interfering with the donor, thereby preserving its optimal morphology. Based on this concept, we designed and synthesized a guest molecule, PPyBT, which incorporates benzodithiophene (BDT) units to ensure donor inertness and 4,5,9,10-pyrene diimide (PyDI) units to guide acceptor packing. PPyBT acts as a multifunctional regulator that not only templates the active layer morphology but also optimizes the energy level alignment. The resulting well-defined phase separation and molecular packing enable the corresponding PM6:L8-BO:PPyBT ternary device to achieve a power conversion efficiency of 19.15%, which is among the highest values reported to date, along with improved stability under both photo- and thermal-stress. This work establishes a feasible molecular framework for guest-induced crystallization control, offering a promising pathway toward high-performance OSCs.