Spectra–Stability Relationships in Organic Electron Acceptors: Excited-State Analysis

The operational stability of organic solar cells critically depends on the excited-state characteristics of electron acceptor materials. Through systematic quantum chemical calculations on four representative acceptors (PCBM, ITIC, Y6, and TBT-26), this study reveals fundamental spectra-stability relationships. Non-fullerene acceptors demonstrate superior light-harvesting with systematically tuned energy levels and significantly lower exciton binding energies (2.05-2.12 eV) compared to PCBM (2.97 eV), facilitating efficient charge separation. Structural dynamics analysis uncovers distinct stability mechanisms: ITIC maintains exceptional structural integrity (anionic RMSD = 0.023, S₁ RMSD = 0.134) with superior bond preservation, ensuring balanced performance-stability. Y6 exhibits substantial structural relaxation in excited states (S₁ RMSD = 0.307, T₁ RMSD = 0.262) despite its low exciton binding energy, indicating significant non-radiative losses. TBT-26 employs selective bond stabilization, preserving acceptor-proximal bonding despite considerable anionic flexibility. These findings establish that optimal molecular design requires both favorable electronic properties and structural preservation in photoactive states, providing crucial guidance for developing efficient and stable organic photovoltaics.