Synergistic Modulation of Intermolecular Interactions and Energetic Disorder Enables 20.05% Efficient Binary Organic Solar Cells.

Abstract

Simultaneously optimizing active layer morphology and suppressing energetic disorder is still a key obstacle to developing high-efficiency non-fullerene organic solar cells (OSCs). To overcome this limitation, we introduce a novel highly electronegative small molecule material containing a pyridyl group, 2,6-dichloro-4-(trifluoromethyl)pyridine (TFFN), into the D18/L8-BO system to regulate the active layer morphology and charge dynamics. Theoretical calculations and experimental results confirm that, owing to its highly electronegative nitrogen atom, the pyridine core of TFFN establishes stronger electrostatic-dominated π-π interactions with the non-fullerene acceptor L8-BO compared to its analog, the benzene-based control small molecule material 3,5-dichlorobenzotrifluoride (TWFCl). These interactions promote more ordered molecular packing and prolong the crystallization time during film formation, effectively improving crystallinity. The optimized morphology of the active layer contributes to balanced charge transport, efficient exciton dissociation, and reduced charge recombination. Consequently, energetic disorder is significantly reduced, enabling the TFFN-treated device to achieve an excellent power conversion efficiency (PCE) of 20.05%, which is a substantial improvement over the control device (18.01%). Moreover, the TFFN-based device exhibits superior thermal stability, retaining 84.82% of its initial PCE after 180 min of heating at 80 °C. This work provides a feasible pathway for the molecular design of highly electronegative small molecules, which can concurrently optimize active layer morphology, mitigate energetic disorder, and boost both the efficiency and stability of OSCs.