High open-circuit voltage solution-processed organic solar cells based on a star-shaped small molecule end-capped with a new rhodanine derivative

A new star-shaped small molecule named TCNR3TTPA, with a triphenylamine (TPA) unit as the central building block and 2-(1,1-dicyanomethylene)-3-octyl rhodanine (CNR) as the end-capped group, has been designed and synthesized. TCNR3TTPA showed a deep highest occupied molecular orbital (HOMO) energy level (-5.60 eV) and broad absorption. The solution-processed bulk heterojunction (BHJ) solar cells based on TCNR3TTPA:PC61BM (1:1, w/w) exhibited a high open-circuit voltage (V (oc)) of 0.99 V, a short-circuit current density (J (sc)) of 5.76 mA/cm(2), and a power conversion efficiency (PCE) of 2.50% under the illumination of AM 1.5 G, 100 mW/cm(2). The high V (oc) is ascribed to the strong electron-with- drawing ability of the end-capped 2-(1,1-dicyanomethylene)-3-octyl rhodanine group. These results demonstrated that the V (oc) of small-molecule organic solar cells could be increased by introducing a strong electron-withdrawing end-capped block, and that this is an effective strategy to design high-performance small molecules for organic solar cells.