Through the combination of central naphthalene diimide and terminal rhodanine or 1,3-indanedione functionalities, two new non-fullerene electron acceptors, coded as N3 and N4, were designed, synthesized and characterized. Both of the materials exhibited good solubility, thermal stability, and displayed energy levels matching those of the conventional and routinely used donor polymer poly(3-hexyl thiophene) (P3HT). A high power conversion efficiency of 4.76% was obtained in simple, solution-processable bulk-heterojunction devices (P3HT : N3 1 : 1.2) which is the best result for central NDI-based small molecular non-fullerene acceptors.