Acceptor-donor-acceptor small molecules containing benzo [1,2-b:4,5-b′]dithiophene and rhodanine units for solution processed organic solar cells

Two novel solution-processed acceptor-donor-acceptor (A-D-A) structured organic molecules with 5,8-disubstituted benzo[1,2-b:4,5-b′]dithiophene (BDT or BDTT) as central and donor units, 2-(1,1-dicyanomethylene)rhodanine (DCRD) as acceptor unit and terminal group, and trithiophene (T₃) as π-bridges, D(T₃-DCRD)-BDT and D(T₃-DCRD)-BDTT, are designed and synthesized for the application as donor materials in organic solar cells (OSCs). Both compounds exhibit broad absorption covering the wavelength range 300-750 nm and the relatively lower HOMO energy levels from -5.39 to -5.46 eV. D(T₃-DCRD)-BDTT demonstrates strong absorbance and higher hole mobility than that of D(T₃-DCRD)-BDT. The power conversion efficiency (PCE) values of the OSCs based on the compounds/PC₆₁BM (1:1, w/w) are 1.10% for D(T₃-DCRD)-BDT and 1.94% for D(T₃-DCRD)-BDTT, under the illumination of AM. 1.5G, 100 mW/cm^-2. Furthermore, the high open-circuit voltage (V_oc) values are 0.93 V for D(T₃-DCRD)-BDT and 0.96 V for D(T₃-DCRD)-BDTT, respectively. It indicates that incorporating DCRD as an acceptor unit into D-A-D-type small molecule has proven to be promising candidates for high efficiency solution processed OSCs.