Modulation of Molecular Quadrupole Moments by Phenyl Side-Chain Fluorination for High-Voltage and High-Performance Organic Solar Cells

The ground-state charge generation (GSCG) in photoactive layers determines whether the photogenerated carriers occupy the deep trap energy levels, which, in turn, affects the device performance of organic solar cells (OSCs). In this work, charge-quadrupole electrostatic interactions are modulated to achieve GSCG through a molecular strategy of introducing different numbers of F atom substitutions on the BTA3 side chain. The results show that 8F substitution (BTA3-8F) and 16F substitution (BTA3-16F) lead to different patterns of highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy level changes. The perfluorination of the phenyl side chain endows BTA3-16F with a LUMO energy level similar to that of BTA3, ensuring a high VOC. Besides, BTA3-16F features a large charge-quadrupole moment, promoting strong electrostatic interactions between neighboring molecules along the π-π stacking direction, which then induces the GSCG in photoactive components. This efficient GSCG directly makes a significant impact on the subsequent kinetics of photogenerated exciton dissociation, recombination, and transport over longer time periods, as well as on nonradiative recombination over larger spatial scales. Benefiting from the favorable GSCG and suitable energy level arrangement, PTQ10/BTA3-16F achieves a VOC of 1.302 V and a PCE of 11.14%, setting the world record for OSCs performance with a VOC greater than 1.3 V. In addition, BTA3-16F is an effective guest molecule to improve the performance of ternary OSCs, and PM6/L8-BO/BTA3-16F-based ternary device achieves the highest PCE of 19.82%. This result emphasizes the important role of GSCG between photoactive components in OSC performance and demonstrates that modulation of molecular quadrupole moments is an effective means of designing efficient acceptors.