Controlling the crystallization of donor and acceptor of organic solar cells during the film-forming and thermal annealing processes by utilizing solid additive

Achieving sufficiently high crystallinity and forming a suitable vertical phase separation in the active layer are essential for optimizing the performance of organic solar cells (OSCs). Nevertheless, achieving precise control of the crystallinity of the active layer without excessive aggregation still remains challenging. Herein, we propose an approach to prolong the crystallization duration of PM6 and L8-BO via a solid additive (OIB) with excellent planarity and volatility. By introducing OIB, the crystallization period of PM6 and L8-BO increased considerably from 0.10 to 0.15 s during the film formation process. Moreover, the molecular motion time of L8-BO was also significantly increased from 4 to 11 s during the thermal annealing procedure. As a result, the incorporation of OIB decreases the π-π stacking distance of PM6 and L8-BO, giving to an improved ordered arrangement of molecules in the active layer. Furthermore, incorporating OIB could improve the arrangement of PM6 molecules, increase their face-on contents, and promote the movement of L8-BO to form a suitable vertical phase separation. Thus, OIB-optimized devices exhibit enhanced charge transport along with reduced bimolecular recombination, leading to an impressive rise in power conversion efficiency from 17.23% to 18.58%.