eC9-2Cl is another highly efficient non-fullerene acceptor that belongs to the Y6 acceptors family.?With a fused thienothienopyrrolo-thienothienoindole (TTP-TTI) core, eC9-2Cl is a sister compound to? BTP-eC9 with two less chlorine atoms on the peripheral benzene end groups. Comparing to BTP-eC9, the absorption of eC9-2Cl is blue shifted for about 20 nm at its maximum absorption with elevated HOMO/LUMO energy levels.