Phosphole Substitution for Enhanced Power Conversion Efficiencies in Organic Solar Cells

The power conversion efficiencies (PCEs) of organic solar cells (OSCs) have recently improved from 10% to ≈20% with non‐fullerene acceptors (NFAs) like “Y6.” To further enhance PCEs for commercial viability, modifications are explored to Y6 by replacing pyrrole units with phospholes, leveraging their lower‐lying lowest unoccupied molecular orbitals (LUMOs) for better electron‐accepting ability. Additionally, terminal fluorine atoms are replaced with electron‐withdrawing groups (EWGs) such as Cl, CF₃, and NO₂, and substituted thiophene units with selenophenes. Using density functional theory (DFT) and time‐dependent functional theory (TDDFT), 13 NFAs are studied, evaluating their optoelectronic properties, including short‐circuit current density (JSC), open‐circuit voltage (VOC), and absorption spectra. Modifications led to red‐shifted absorption, improved JSC, and relatively stable VOC values. The PM6/Y6‐P‐Cl system exhibits the highest PCE of 18.46%. This study highlights the potential for further improving Y6‐based OSCs, advancing solar energy efficiency (SDG 7), and contributing to clean energy solutions (SDG 13).