Electrostatic Potential Site Effect of the Third Component Enables High-Performance Organic Solar Cells with Low Energy Loss.

Organic solar cells (OSCs) are typically plagued by substantial non-radiative energy loss (ΔE3) during the photoelectric conversion process, which limits further performance improvement. While incorporating a third component can effectively optimize active layer morphology and suppress non‑radiative recombination, the selection of such components currently lacks precise theoretical guidance. To address this challenge, we propose a new concept of electrostatic potential (ESP) site effect, which enables modulation of local ESP distribution by precisely adjusting terminal substituent positions without altering average molecular ESP, energy levels, or absorption. Guided by this concept, two asymmetric acceptors, ZY-SCF3-N2F and ZY-SCF3-B2F, were rationally designed and incorporated as the third component into the PM6/BTP-eC9 system. Combining theoretical and experimental results reveal that both acceptors possess large dipole moments that favor ΔE3 suppression. Notably, ZY-SCF3-B2F, featuring a larger ESP difference at terminal carbon atoms, induces more ordered molecular packing and favorable phase separation morphology in the ternary blend. This leads to synergistic enhancements in open‑circuit voltage, short‑circuit current density, and fill factor, ultimately delivering an outstanding efficiency of 20.53%. This work elucidates the critical role of local ESP distribution in determining material properties and provides a simple yet effective theoretical guideline for developing highly efficient ternary OSCs.