Synthesis and Characterization of Dioctyloxybenzo[1,2-b:4,3-b′]-dithiophene-Containing Copolymers for Polymer Solar Cells

A series of D-A copolymers containing dioctyloxybenzo[1,2-b:4,3-b']dithiophene (BdT) donor unit and different acceptor unit of bithiazole (BTz), thiazolo[5,4-d]-thiazole (TTz), dithienylylbenzothiadiazole (DTBT), and dithienyl-pyrrolo[3,4-c]pyrrole-1,4-dione (DPP), PBdT-BTz, PBdT-TTz, PBdT-DTBT, and PBdT-DPP, were synthesized for the application as donor materials in polymer solar cells (PSCs). Bandgaps and HOMO (the highest occupied molecular orbital) energy levels of the copolymers were tuned effectively by using different acceptor units from 2.01 and -5.16 eV for PBdT-BTz, to 1.91 and -5.19 eV for PBdT-TTz, 1.70 and -5.09 eV for PBdT-DTBT, and 1.41 and -5.01 eV for PBdT-DPP. The PSCs based on the blend of PBdT-TTz (with a lower HOMO of -5.19 eV) and PC70BM (1:3 w/w) exhibited a power conversion efficiency of 3.40% with a J(sc) of 5.50 mA/cm(2), a high V-oc of 0.90 V, and a high FF of 68.7%.