Theoretical investigations of the small molecular acceptor materials based on oligothiophene – naphthalene diimide in organic solar cells

Abstract

A series of novel acceptor–donor–acceptor–donor–acceptor (A₂–D–A₁–D–A₂) structured acceptor oligomers with naphthalene diimide (NDI) as centre and acceptor unit (A₁), oligothiophenes (T = 1, 2, 3, 4) as π-bridges (D), and 2-(1,1-dicyanomethylene)rhodanine (DCRD) as terminal groups (A₂) have been investigated using quantum chemistry and Marcus theory in this research. Compared with NDI-2T₁Me—NDI-2T₄Me, the NDI-2T₁DCRD—NDI-2T₄DCRD exhibit stronger and wider absorption peaks because of the increase of the electron withdrawing ability of the electron deficient units. In particular for the NDI-2T₃DCRD, the electron mobility (μ_e = 5.71 × 10⁻³ cm² V⁻¹ S⁻¹) was accurately predicted quantitatively using first principle simulation. The blend of poly(3-hexylthiophene) with NDI-2T₃DCRD as an active layer exhibits obviously strong and wide light absorption, which form a perfectly complementary absorption. The results indicate that the incorporation of DCRD as acceptor units into D–A–D type oligomers has been proven to create promising candidates for high efficiency acceptor materials for organic solar cells (OSCs). Overall, this research may provide a theoretical guidance for designing small molecular acceptors for OSC applications.