All-Small-Molecule Organic Solar Cells with an Ordered Liquid Crystalline Donor

Summary The crystallinity and intermolecular interaction among small molecules are enhanced in order to achieve reasonable phase segregation between the donor and acceptor in all-small-molecule organic solar cells (ASM OSCs). By substituting an alkyl side chain with a chlorine (Cl) atom on the original benzodithiophene terthiophene rhodanine (BTR) molecule, the new small molecular donor, namely BTR-Cl, processes a more ordered liquid crystalline property, down-shifted molecular energy levels, and higher crystallinity. When blended with a non-fullerene acceptor Y6, which has a complementary absorption profile and well-matched energy levels but no liquid crystalline property, a prominent phase separation and optimal film morphology are obtained. As a result, a record-high power conversion efficiency (PCE) of 13.6% is achieved, taking a large step forward in ASM OSCs. Our results highlight the importance of crystallinity to phase separation, suggesting the great promise of liquid crystalline materials in OSCs.