Synthesis and photovoltaic properties of D-A copolymers based on alkylthio-thiophene or alkylthio-selenophene-BDT donor unit and DPP acceptor unit

• Two 2D-conjugated D-A copolymers, PBDTT-S-DPP and PBDTSe-S-DPP with alkylthio substituent, were synthesized.
• The side chain engineering plays important roles in affecting the absorption and HOMO energy levels of the polymers.
• The PSCs based on PBDTT-S-DPP as donor and PC71BM as acceptor demonstrate PCE of 5.62% with relatively higher Voc of 0.79 V.

Two new 2D-conjugated D-A copolymers, PBDTT-S-DPP and PBDTSe-S-DPP, based on benzodithiophene (BDT) donor unit with alkylthio-thiophene or alkylthio-selenophene conjugated side chains and 2,5-bis(2-butyloctyl)-3,6-di(thiophen-2-yl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione) (DPP) acceptor unit, were synthesized for the application as donor materials in polymer solar cells (PSCs). The two polymers were characterized by absorption spectroscopy, cyclic voltammetry, thermogravimetric analysis, theoretical calculation with density functional theory, X-ray diffraction and photovoltaic measurements. The results show that the alkylthio-thiophene/selenophene side groups on BDT unit and intramolecular hydrogen bonding interaction in DPP acceptor unit play important roles in affecting the absorption, HOMO energy levels, molecular planarity and the crystallinity of the polymers. The PSCs based on PBDTT-S-DPP or PBDTSe-S-DPP as donor and PC71BM as acceptor demonstrate power conversion efficiency (PCE) of 5.62% and 5.01%, with relatively higher Voc of 0.79 V and 0.76 V, respectively.

Two new 2D-conjugated D-A copolymers, PBDTT-S-DPP and PBDTSe-S-DPP, based on 2D-BDT donor unit and DPP acceptor unit, were synthesized for the application as donor materials in polymer solar cells (PSCs). The results reveal that integrating the 2D-BDT with alkylthio side chain and DPP acceptor unit in one polymer can effectively lower the HOMO energy level, improve the coplanarity and increase the crystallinity of the polymers. The PSCs based on PBDTT-S-DPP or PBDTSe-S-DPP/PC71BM demonstrated PCE of 5.62% and 5.01%, with a higher Voc of 0.79 V and 0.76 V, respectively.Figure optionsDownload as PowerPoint slide