Rational design of novel A-A-D-A-A type electron donors for small molecule organic solar cells

We theoretically designed four new A-A-D-A-A type electron donors by side-by-side combination of strong electron-withdrawing groups. The electronic structures and optical absorption spectra of donors were calculated using density functional theory (DFT) and time-dependent DFT (TDDFT) at the 6-31G∗ level, respectively. The results show that the calculations are in good agreement with the experiments on electronic structures and optical spectra. The designed molecules exhibit good properties with low band gap, low LUMO energy level, and broad light absorption. Moreover, the estimated solar cell efficiency is up to ∼10% when these donors are used in combination with PCBM as an acceptor.