Synthesis and Photovoltaic Properties of D-A Copolymers Based on Alkyl-Substituted Indacenodithiophene Donor Unit

Four D-A copolymers of tetradodecyl-substituted indacenodithiophene (IDT) donor unit with different acceptor units including bis(thiophen-2-yl)-bithiazole (BT2), bis(thiophen-2-yl)thiazolothiazole (TTz), bis(thiophen-2-yl)-tetrazine (TZ), and bis(thiophen-2-yl)-benzothiadiazole (DTBT), PIDT-BTz, PIDT-TTz, PIDT-TZ, and PIDT-DTBT, were synthesized for the application as donor materials in polymer solar cells (PSCs). The copolymers possess good solubility benefitted from the four alkyl side chains on IDT unit, deeper HOMO levels at ca. -5.2 eV thanks to the IDT unit and tunable bandgap depending on the acceptor units. Among the copolymers, PIDT-TTz has the highest hole mobility (mu(h)) of 4.99 x 10(-3) cm(2)/V s. The power conversion efficiency (PCE) of the PSC based on PIDT-TTz/PC70BM (1:2 w/w) reached 5.79%, under the illumination of AM1.5G, 100 mW/cm(2). PIDT-DTBT film has the smallest bandgap of 1.68 eV and a higher mu(h) of 2.24 x 10(-3) cm(2)/V s. The PSC based on PIDT-DTBT/PC70BM (1:3 w/w) exhibited an even higher PCE of 6.17% with a J(sc) of 13.27 mA/cm(2), a V., of 0.82 V-oc and a FF of 56.9%.