Deciphering the role of tilde-shaped rhodanine-based non-fullerene acceptor materials for efficient organic photovoltaics.

The development of small-molecule-based (SM) energy-efficient non-fullerene acceptors (NFAs) for organic solar cells (OSCs) has gained significant attention. In this study, we designed a series of seven novel rhodanine-based SM-NFAs (IC1-IC7) and compared them with the synthetic reference molecule (IC-R). By incorporating diverse end-capped functional groups, we tailored their optical, photophysical, optoelectronic, and photovoltaic properties. Advanced quantum chemical simulations, including density functional theory (DFT) and time-dependent DFT (TD-DFT), are used to assess the impact of side-chain and bridged-core modifications. We analyzed binding energies, electron-hole reorganization energies, electrostatic potential, and transition density. Additionally, we investigated electronic transitions through a natural population, natural bond orbital, electron density difference, and intra-molecular charge transfer analyses. Compared to IC-R, the designed NFAs exhibited lower binding energies (1.15 eV), narrower band gaps (3.24 eV), enhanced absorbance (590.88-625.87 nm), and reduced electron and hole mobilities. A donor-acceptor complex analysis of PTB7-Th:IC-6 further explored charge transfer mechanisms. These findings suggest that IC1-IC7 have the potential to achieve improved open-circuit voltages and fill factor values, which will ultimately boost their power conversion efficiencies, making them promising candidates for next-generation high-performance OSCs.