A₁-A-A₁ type small molecules terminated with naphthalimide building blocks for efficient non-fullerene organic solar cells

Novel non-fullerene acceptors with an A₁-A-A₁ framework were designed and synthesized, in which benzothiadiazole and diketopyrrolopyrrole building blocks were employed as the A unit and naphthalimide units were incorporated as the A₁ units. Both acceptor systems exhibited a broadened absorption spectra from 300 nm to 700 nm in contrast to that of fullerene derivatives. Meanwhile, high-lying LUMO energy levels were also observed for both developed acceptors. To investigate photovoltaic properties of the acceptors, bulk-heterojunction organic solar cells were fabricated using an established electron donating polymer as the donor material. As anticipated, efficient non-fullerene OSCs with high V_oc values up to 1.01–1.12 V were achieved when the new molecules were employed as electron acceptors, leading to the PCE values of 1.23% and 1.64% in their solar cells. Our results here demonstrate that the A₁-A-A₁ type small molecule containing naphthalimide building blocks in molecular backbone could be the promising electron acceptor in organic solar cells.