Terminal group engineering of dipyran-based non-fullerene acceptors: a computational approach for high performance organic solar cells

Abstract

Achieving high power conversion efficiency (PCE) remains a major challenge in the development of organic solar cells (OSCs). While non-fullerene acceptors (NFAs) have demonstrated significant progress, innovative molecular strategies are still required to overcome limitations in spectral coverage, charge transport, and interfacial energetics. Here, we propose a dipyran-centered molecular design approach and introduce seven novel asymmetric A–D–π–A NFAs, systematically engineered through terminal-acceptor modifications. Density functional theory (DFT) and time-dependent DFT (TD-DFT) methods have been adopted in both gas and solvent phases to evaluate their electronic, optical, and photovoltaic (PV) properties. Among the designed molecules, DP1 exhibits the narrowest HOMO–LUMO gap (E_g = 1.85 eV) and the lowest exciton binding energy (E_b = 0.30 eV), favoring efficient exciton dissociation. DP2 shows the most red shifted absorption (λ_max = 888 nm) along with the lowest electron reorganization energy (λ_e = 0.0040 eV), ensuring broad solar spectrum utilization and efficient charge transport. DP5 demonstrates the highest light harvesting efficiency (LHE = 0.999462) and strong oscillator strength (f = 3.269), while also achieving the highest fill factor (FF = 99.1%), indicating robust photon absorption and charge collection. DP7 delivers the highest open circuit voltage (V_oc = 1.71 V) with a strong fill factor (FF = 92.3%), providing excellent voltage headroom. Additionally, DP3 exhibits the largest dipole moment (11.417 D in solvent), which enhances intramolecular charge transfer (ICT) and polarity driven separation. Compared to the reference molecule R, all designed NFAs exhibit reduced E_g, red shifted λ_max, stronger ICT, and improved charge mobilities. Overall, this work highlights dipyran-based asymmetric NFAs as strong candidates for next generation OSCs and provides a theoretical framework for guiding the rational design of high efficiency PV materials.