Synthesis and photovoltaic properties of alkylthiothienyl-substituted benzo[1,2-b:4,5-b′]dithiophene D–A copolymers with different accepting units

• A series of low bandgap D–A copolymers based on alkylthiothienyl-substituted benzo[1,2-b:4,5-b′]dithiophene (BDTS) and different acceptor units were developed for PSCs.
• Optoelectronic properties of these D–A copolymers can be easily tailored by varying the different acceptor units.
• The BDTS-based polymers possess narrow bandgap, low-lying HOMO energy level and high hole mobility.
• The best PSC based on these copolymers shows a power conversion efficiency (PCE) of 3.19%.

A series of low bandgap donor–acceptor (D–A) copolymers (PBDTSFBT, PBDTS-DTFBT, PBDTS-TPD, and PBDTS-DPP) composed of alkylthiothienylsubstituted benzo[1,2-b:4,5-b′]dithiophene (BDTS) as the electron rich donor unit combined with different electron deficient acceptor building blocks are developed for polymer solar cell (PSC) applications. The effects of accepting unit on the optical, electrochemical, energy levels and photovoltaic properties of the copolymers were investigated in detail. The BDTS-based polymers possess good solubility in common organic solvents and excellent thermal stability. These polymers show narrow bandgap (1.45 – 1.88 eV), low-lying HOMO energy level (−5.30 to −5.51 eV) and higher hole mobility (1.14 × 10−3−1.72 × 10−2 cm2 V−1 s−1). The screening of the processing additive (1,8-diiodooctane) and polar solvent (methanol) post-treatment was conducted to optimize the PSC devices. The best PSC based on the copolymer PBDTS-DTFBT and PC70BM showed a power conversion efficiency (PCE) of 3.19% with a Voc of 0.83 V, a Jsc of 8.27 mA/cm2 and a FF of 46.42%.

A series of donor–acceptor (D–A) conjugated copolymers (PBDTS-FBT, PBDTS-DTFBT, PBDTS-TPD, and PBDTS-DPP) based on an efficient donor unit of alkylthiothienyl-substituted benzo[1,2-b:4,5-b′]dithiophene (BDTS) and different acceptor units of fluorinated benzothiadiazole (FBT), thieno[3,4-c]-pyrrole-4,6-dione (TPD), or pyrrolo[3,4-c]pyrrole-1,4-dione (DPP), were synthesized and characterized as donor in polymer solar cells (PSCs). The effect of different acceptor units on the physicochemical properties of the polymers was investigated systematically. The PSCs based on PBDTS-DTFBT:PC70BM gave the highest PCE of 3.19%.Figure optionsDownload as PowerPoint slide