Effect of Phosphole Substitution on the Power Conversion Efficiencies of Y6 and its derivatives

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, we explored modifications to Y6 by replacing pyrrole units with phospholes, leveraging their lower-lying LUMOs for better electron- accepting ability. Additionally, we replaced terminal fluorine atoms with electron- withdrawing groups (EWGs) such as Cl, CF₃, and NO₂, and substituted thiophene units with selenophenes. Using DFT and TDDFT, we studied 13 NFAs, 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 exhibited 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).