Synthesis and photovoltaic properties of new small molecules with rhodanine derivative as the end-capped blocks

Two new acceptor–donor–acceptor (A–D–A) type small molecules DCAO3TIDT and DCNR3TIDT, with 4,4,9,9-tetrakis(4-(dodecyloxy)phenyl)-4,9-dihydro-s-indaceno-[1,2-b:5,6-b′]dithiophene (IDT) as the core group and 2-ethylhexyl cyanoacetate (CAO) and 2-(1,1-dicyanomethylene)-3-octyl rhodanine (CNR) as different end-capped blocks, have been designed and synthesized. Both of them have been employed as donor for solution-processed bulk hetero-junction (BHJ) organic solar cells (OSCs). The two compounds showed deep highest occupied molecular orbital (HOMO) energy levels (∼−5.30   eV) and strong absorption. The DCAO3TIDT and DCNR3TIDT with PC 71 BM as acceptor based BHJ solar cell devices showed short circuit current density ( J sc ) of 6.93   mA/cm 2 and 8.59   mA/cm 2 , power conversion efficiency (PCE) of 3.34% and 4.27%, respectively, and with almost same open-circuit voltage (∼0.93   V), under the illumination of AM 1.5   G, 100   mW/cm 2 . The high J sc for DCNR3TIDT could result from its wider and red-shifted absorption than that of DCAO3TIDT, which was probably induced by the end-capped block rhodanine derivative. The results demonstrate that the end group would be taken into full account when designing new solution-processed small molecules, which is an important factor to determine their photovoltaic properties.