Low Band Gap Polymers Incorporating a Dicarboxylic Imide-Derived Acceptor Moiety for Efficient Polymer Solar Cells

Abstract

Two novel copolymers incorporating N-alkyl-4,7-di(thien-2-yl)-2,1,3-benzothiadiazole-5,6-dicarboxylic imide (DI) and benzo[1,2-b:4,5-b′]dithiophene (BDT) units have been designed, synthesized, and characterized. By the incorporation of the DI unit, both polymers show a bathochromically shifted absorption with a deep lying highest occupied molecular orbital (HOMO) energy level. The polymer based on thienyl group substituted BDT exhibits an intense absorption in the longer-wavelength region, a deeper lying HOMO energy level, and a higher carrier mobility, all of which contribute to the resulting polymer solar cells with a higher power conversion efficiency (PCE) of 5.19% and an increased V oc of 0.91 V.

Syntheses of pyrimidine‐based polymers containing electron‐withdrawing substituent with high open circuit voltage and applications for polymer solar cells

“…After concentration of the organic phase under reduced pressure, the residue was purified by column chromatography to give 0.5 g (28%) of compound 10 as yellow oil. (3) (1 eq), 4,6-bis(5-bromo-4-hexyl-2-thienyl)-2-pyrimidinecarbonitrile (9) (1 eq), P(o-tolyl) 3 (0.4 eq) and Pd 2 (dba) 3 (3 mol %) were dissolved in chlorobenzene. The reaction mixture was refluxed with vigorous stirring for 2 days under argon atmosphere.…”

“…The resulting solid material was reprecipitated using 100 mL of chloroform/1.0 L of methanol several times to remove residual amount of the catalyst. The solid was washed for 2 days in a Soxhlet extractor using an (5) (1 eq), 4,6-bis(5-bromo-4-hexyl-2-thienyl)-2-pyrimidinecarbonitrile (9) (1 eq), P(o-tolyl) 3 (0.4 eq), and Pd 2 (dba) 3 (3 mol %) were dissolved in chlorobenzene. The reaction mixture was refluxed with vigorous stirring for 2 days under argon atmosphere.…”

“…The resulting polymer was soluble in THF, CHCl 3 , ODCB, and toluene. (11) (1 eq), P(o-tolyl) 3 (0.4 eq), and Pd 2 (dba) 3 (3 mol %) were dissolved in chlorobenzene. The reaction mixture was refluxed with vigorous stirring for 2 days under argon atmosphere.…”

“…BDT-based copolymers have been reported to provide PSCs with PCE values up to 9%. [3][4][5][6] Many types of electron-deficient units, including 2,1,3-benzothiadiazole, 7 diketopyrrolo[3,4-c]-pyrrole-1,4-dione, 8 and thieno [3,4-c]pyrrole-4,6-dione, 9 have been reported for the D-A type of low band-gap polymers. 10 Among them, compounds containing pyrimidine unit have been studied as promising materials to present a compact stacking for high mobility owing to coplanar conformation.…”

“…3,11 In case of pyrimidines in which CBN or fluorine was introduced, the cyano group and fluorine groups are strong acceptor units to provide properties of higher conjugation, coplanarity, and rigidity. 6,11 In this article, we report D-A types of conjugated polymers, PBDTCN, PBDTTCN, PBDTF, and PBDTTF, containing BDT or BDTT as donor (D) unit and 2-pyriminecarbonitrile or 2-fluoropyrimidine as acceptor (A) unit (Schemes 1 and 2).…”