Bis(thienothiophenyl) Diketopyrrolopyrrole-Based Conjugated Polymers with Various Branched Alkyl Side Chains and Their Applications in Thin-Film Transistors and Polymer Solar Cells

Abstract

New thienothiophene-flanked diketopyrrolopyrrole and thiophene-containing π-extended conjugated polymers with various branched alkyl side-chains were successfully synthesized. 2-Octyldodecyl, 2-decyltetradecyl, 2-tetradecylhexadecyl, 2-hexadecyloctadecyl, and 2-octadecyldocosyl groups were selected as the side-chain moieties and were anchored to the N-positions of the thienothiophene-flanked diketopyrrolopyrrole unit. All five polymers were found to be soluble owing to the bulkiness of the side chains. The thin-film transistor based on the 2-tetradecylhexadecyl-substituted polymer showed the highest hole mobility of 1.92 cm2 V(-1) s(-1) due to it having the smallest π-π stacking distance between the polymer chains, which was determined by grazing incidence X-ray diffraction. Bulk heterojunction polymer solar cells incorporating [6,6]-phenyl-C71-butyric acid methyl ester as the n-type molecule and the additive 1,8-diiodooctane (1 vol %) were also constructed from the synthesized polymers without thermal annealing; the device containing the 2-octyldodecyl-substituted polymer exhibited the highest power conversion efficiency of 5.8%. Although all the polymers showed similar physical properties, their device performance was clearly influenced by the sizes of the branched alkyl side-chain groups.

Effect of Alkyl Chain Branching Point on 3D Crystallinity in High N‐Type Mobility Indolonaphthyridine Polymers

“…Vezie et al furthered this study showing how the high persistence length of the branching‐point‐extended polymer contributed strongly to its notably high optical absorption properties . Conversely, Shin et al reported a decrease in OPV efficiency of the same polymer where the branching point was held constant, but the total chain length was extended . Their chain‐length‐extended DPPTTT exhibited coarse microstructure with large degrees of phase separation in the OPV active layer, leading to a decrease in current density and thus efficiency.…”

“…Although the influence of alkyl chains on nanostructure is unique to each monomer/co‐polymer family, general correlations have been drawn thanks to the vast library of polymers and chains available in the literature ( Figure ). The length of an alkyl chain, whether it is purely linear or contains a branched chain, and the length of chain before the branching point (the spacer length) can all be considered when designing a novel monomer, and each factor directly affects charge transporting properties, in some cases resulting in improvements of charge carrier mobilities of more than several orders of magnitude in organic field‐effect transistors (OFETs) and increases in organic photovoltaic (OPV) efficiencies of several percentages . Other strategies, such as the construction of asymmetrically alkylated monomers (poly[2‐methoxy‐5‐(2‐ethylhexyloxy)‐1,4‐phenylenevinylene] MEH‐PPV, 1k ), the use of heteroatoms (e.g., polyethylene glycol, 1j ) or electronegative atoms (e.g., F, 1i ), have also been explored but impose more complex synthetic strategy and a higher economic cost.…”

Intermolecular Arrangement of Fullerene Acceptors Proximal to Semiconducting Polymers in Mixed Bulk Heterojunctions

“…Alkyl side chains, the primary function of which is to make polymers soluble, can affect the OPV performance, and sometimes substantially. The length, size, and shape of the alkyl chains on the main chains affect intermolecular packing, orientation, and morphology in the mixed BHJ films, which are important factors in OPV performance . Graham et al.…”

Intermolecular Arrangement of Fullerene Acceptors Proximal to Semiconducting Polymers in Mixed Bulk Heterojunctions

“…[14][15][16][17][18][19] Therefore,t he spatial arrangement of the donor and acceptor can strongly affect the photophysical and electronic processes in OPVs,a s suggested by theoretical calculations [20][21][22] and experimental studies using planar heterojunctions as model systems. [28][29][30][31] Graham et al hypothesized that the bulkiness of the alkyl side chains in D-A copolymers may also affect the position of the acceptor molecules around the polymers. [27] Controlling the interfacial structures is even more challenging in BHJs.…”

“…[28][29][30][31] Graham et al hypothesized that the bulkiness of the alkyl side chains in D-A copolymers may also affect the position of the acceptor molecules around the polymers. [28][29][30][31] Graham et al hypothesized that the bulkiness of the alkyl side chains in D-A copolymers may also affect the position of the acceptor molecules around the polymers.…”