A novel non-fullerene small molecule acceptor, TITI-4F, containing a N,N-dialkyl thieno[3′,2′:2,3]indolo[7,6-g]thieno[3,2-b]indole (TITI) core, was designed and synthesized. Photovoltaic devices based on PM6:TITI-4F can realize a high FF of 0.75, and a PCE of 10.89%. Our work demonstrates that TITI is a promising fused core for high quality acceptors.