Ultra-narrow bandgap D-A copolymer based on thienoisoindigo acceptor unit for application in polymer solar cells with energy losses below 0.6 eV

• A new 2D-conjugated D-A copolymer PBDTT-TIID based TIID acceptor unit was synthesized;.
• PBDTT-TIID possesses a very narrow bandgap of 1.17 eV and a higher hole mobility of 4.48 × 10−3 cm2/V s.
• The PSCs based on PBDTT-TIID:PC71BM demonstrate a higher Voc of 0.59 V, corresponding to a low energy loss of 0.58 eV.

A new ultra-narrow bandgap and 2D-conjugated D-A copolymer, PBDTT-TIID, based on bithienyl-benzodithiophene (BDTT) donor unit and (E)-4,4′-bis(2-ethylhexyl)-[6,6′-bithieno[3,2-b]pyrrolylidene]-5,5′(4H,4′H)-dione (TIID) acceptor unit was designed and synthesized for the application as donor material in polymer solar cells (PSCs). The polymer demonstrates two absorption peaks at around 450 nm and 900 nm respectively, and possesses a very narrow bandgap (Eg) of 1.17 eV and a higher hole mobility of 4.48 × 10−3 cm2/V s. The PSCs based on PBDTT-TIID:PC71BM (1:1, w/w) demonstrate a higher Voc of 0.59 V even though the polymer has a very narrow Eg of 1.17 eV, which is corresponding to a low energy loss (Eloss) of 0.58 eV. In addition, an optimal PCE of 2.40% was achieved with 1% DIO as additive.

A new ultra-narrow bandgap D-A copolymer, PBDTT-TIID, was designed and synthesized for the application as donor material in PSCs. The PCE of the devices reached 2.40% with a higher Voc of 0.57–0.59 V, and very importantly, the Eloss of the devices is only 0.58–0.60 eV, which is the highest Voc value among TIID-based polymers with an ultra-narrow bandgap of 1.17 eV reported in the literature so far.Figure optionsDownload as PowerPoint slide