Designing new donor materials based on functionalized DCCnT with different electron-donating groups: A density functional theory (DFT) and time dependent density functional theory (TDDFT)-based study

Finding a promising donor/acceptor material of organic solar cells is one of the most important ways to improve their power conversion efficiency. Extensive studies have focused on designing and synthesizing new and suitable materials. Small organic molecule materials, different from polymers, have many merits, such as easy synthesis and modification, less by-products, and crystallinity. In the present work, we theoretically design a series of new donor materials based on 1-(1,1-dicyanomethylene)-cyclohex-2-ene-substituted oligothiophenes, that is, DCCnT (n = 1-4) series. Furthermore, we model and predict photoelectric properties of functionalized DCCnT with different electron-donating groups (─CH₃/─CH?CH₂/─OCH₃/─NH₂/─OH). The calculated results, based on density functional theory and time-dependent functional theory, show that DCCnT-X (X = OH, NH₂, and OCH₃) series show odd-even effect of dipole moments when n varies from 1 to 4, whereas DCCnT-CH₃ and DCCnT-CH?CH₂ do not. Finally, we find that DCC3T-X (X = OH, OCH₃, and NH₂) may be better candidates of donor materials because of their larger dipole moments, stronger electron donating ability, and smaller exciton binding energy with respect to prototype DCCnT molecules.