High-performing random terpolymer-based nonfullerene polymer solar cells fabricated using solvent additive-free as-cast blend films

Abstract

Two new random terpolymers containing 4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b:4,5-b]dithiophene (BDT) as a donating unit, methyl-3-thiophenecarboxylate (3MT) as a weak accepting unit, and the more electron-deficient benzo[c][1,2,5]thiadiazole (BTz) or 5,5-bis(2-ethylhexyl)-4H,4H-1,1-bithieno[3,4-c]pyrrole-4,4,6,6(5H,5H)-tetraone (BiTPD) unit as a third monomer (respectively yielding 3MTB and 3MTT) were synthesized in order to achieve improved physical and optoelectronic properties relative to the 3MT-Th copolymer bearing only BDT and 3MT. The UV-vis absorption spectra and optical bandgap energies of these terpolymers were broader and smaller than those of the 3MT-Th copolymer. In thin films, the terpolymers displayed the face-on polymer chain orientation, indicating that the BTz or BiTPD unit in the terpolymer backbones did not affect the molecular arrangement on the substrate. In comparison with 3MT-Th-based polymer solar cells (PSCs) as control devices, the PSCs employing blend films of these terpolymers as the donor and 2,2-[[6,6,12,12-Tetrakis(4-hexylphenyl)-6,12-dihydrodithieno[2,3-d:2,3-d]-s-indaceno[1,2-b:5,6-b]dithiophene-2,8-diyl]bis[methylidyne(3-oxo-1H-indene-2,1(3H)-diylidene)]]bis[propanedinitrile] (ITIC) as the acceptor exhibited higher power conversion efficiencies (>8.0%) for the same device configuration. In addition, the 3MTB- and 3MTT-based PSC devices displayed excellent shelf-life even after aging for over 1000 h. (c) 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018, 56, 1528-1535