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 small molecules with benzo[1,2-b:4,5-b']dithiophene and rhodanine units were developed.
• Both small molecules exhibited outstandingly Voc about 0.93–0.96 V in BHJ-OSCs.
• The D(T3-DCRD)-BDTT/P61CBM based cells exhibited the maximum PCE of 1.94% and hole mobility of 6.22 × 10−4 cm2 V−1 s−1.
• Introducing DCRD as acceptor unit and BDTT as donor unit are promising materials for the BHJ-OSCs.

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 (Voc) 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.

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