Ethynylene-Linked Donor–Acceptor Alternating Copolymers

Abstract

Controlling steric interactions between neighboring repeat units in donor–acceptor (D–A) alternating copolymers can positively impact morphologies and intermolecular electronic interactions necessary to obtain high performances in organic photovoltaic (OPV) devices. Herein, we design and synthesize 12 new conjugated D–A copolymers, employing ethynylene linkages for this control. We explore D–A combinations of fluorene, benzodithiophene, and diketopyrrolopyrrole with analogues of pyromellitic diimide, thienoisoindoledione, isothianaphthene, thienopyrazine, and thienopyrroledione. Computational modeling suggests the ethynylene-containing polymers can adopt virtually planar conformations, while many of the analogous polyarylenes lacking the ethynylene linkage are predicted to have quite twisted backbones (>35°). The introduction of ethynylene linkages into these D–A systems universally results in a significant blue-shift in the absorbance spectra (by as much as 100 nm) and a deeper HOMO value (∼0.1 eV) as compared to the polyarylene analogues. The contactless time-resolved microwave conductivity technique is used to measure the photoconductance of polymer/fullerene blends and is further discussed as a tool for screening potential active layer materials for OPV devices. Finally, we demonstrate that an ethynylene-linked alternating copolymer of diketopyrrolopyrrole and thienopyrroledione, with a rather deep LUMO estimated at −4.2 eV, shows increased photoconductance when blended with a perfluoroalkyl fullerene C60(CF3)2 as compared to the standard PC61BM. We attribute the change in increased free carrier generation to the higher electron affinity of C60(CF3)2 that is more appropriately matched with the deeper LUMO of the polymer.

π-Linkage effect of push-pull-structure organic small molecules for photovoltaic application

“…Besides, OSMs will receive high V OC which were benefited from the deep-lying HOMO level caused by the electron-withdrawing effect of alkyne. Hence, alkyne including acetylene and arylacetylenes is a promising class of π-bridge [78][79][80][81][82][83]. Fig.…”

Deep Absorbing Porphyrin Small Molecule for High-Performance Organic Solar Cells with Very Low Energy Losses

“…33 In this contribution, two diketopyrrolopyrrole (DPP) units are linked to the both sides of a porphyrin core to extend the π-conjugation via ethynylene bridge, whose functions are two-fold 34,35 (1) introducing sp 1 carbon hybridization can be effective in lowering the highest occupied molecular orbital (HOMO) energy level of the target materials since there are more s-orbital components; and (2) its fluent cylinderlike π-electron density is more adaptable to conformational and steric constrains, and thus to enhance inter-molecular π-π stacking and facilitate intramolecular charge transport. Since it has been reported that thienyl substituents can enhance the OSC's performance, two thienyl groups with a 2-ethylhexyl substituent are introduced into the porphyrin core with added benefit of improving material's solubility.…”

Donor–acceptor semiconducting polymers based on pyromellitic diimide

“…Reich synthesized a 3,6 and N , N ′‐linked pyromellitic diimide polymer which gave an electron‐carrier mobility of 10 −3 to 10 −2 cm 2 V −1 s −1 when the polymer was blended with Phenyl‐C61‐butyric acid methyl ester (PC 61 BM) in a weight ratio of 1:9. This lower charge carrier mobility may be owing to the twist in the neighboring conjugated units in the polymer backbone which result in a decrease in the conjugation . Thus, the insertion of ethynyl linkages at 3,6‐positions on the pyromellitic diimides can decrease the steric and electronic repulsions and is expected to provide a more planar polymer backbone .…”