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1. Achieving High Performance Stretchable Conjugated Polymers via Donor Structure Engineering

   https://doi.org/10.1002/marc.202300169  

   Wu, Ning; Huang, Gang; Huang, Hua; Wang, Yunfei; Gu, Xiaodan; Wang, Xiaohong; Qiu, Longzhen (May 2023, Macromolecular Rapid Communications)

   Abstract A backbone engineering strategy is developed to tune the mechanical and electrical properties of conjugated polymer semiconductors. Four Donor–Acceptor (D–A) polymers, named PTDPPSe, PTDPPTT, PTDPPBT, and PTDPPTVT, are synthesized using selenophene (Se), thienothiophene (TT), bithiophene (BT), and thienylenevinylenethiophene (TVT) as the donors and siloxane side chain modified diketopyrrolopyrrole (DPP) as acceptor. The influences of the donor structure on the polymer energy level, film morphology, molecular stacking, carrier transport properties, and tensile properties are all examined. The films of PTDPPSe show the best stretchability with crack‐onset‐strain greater than 100%, but the worst electrical properties with a mobility of only 0.54 cm² V⁻¹ s⁻¹. The replacement of the Se donor with larger conjugated donors, that is, TT, BT, and TVT, significantly improves the mobility of conjugated polymers but also leads to reduced stretchability. Remarkably, PTDPPBT exhibits moderate stretchability with crack‐onset‐strain ≈50% and excellent electrical properties. At 50% strain, it has a mobility of 2.37 cm²V⁻¹ s⁻¹parallel to the stretched direction, which is higher than the mobility of most stretchable conjugated polymers in this stretching state. 

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2. Pairing 1D/2D-conjugation donors/acceptors towards high-performance organic solar cells

   https://doi.org/10.1039/c8qm00512e  

   Wang, Jiayu; Xiao, Yiqun; Wang, Wei; Yan, Cenqi; Rech, Jeromy; Zhang, Mingyu; You, Wei; Lu, Xinhui; Zhan, Xiaowei (January 2019, Materials Chemistry Frontiers)

   Two polymer donors, FTAZ and J71 , and two fused-ring electron acceptors, ITIC1 and ITIC2 , are used to investigate the effects of conjugation dimension on the performance of organic solar cells (OSCs). FTAZ and J71 , and ITIC1 and ITIC2 share the same molecular backbone, respectively, while J71 and ITIC2 possess conjugated thienyl side chains. The addition of conjugated side chains slightly red-shifts the absorption spectra and lowers the bandgap due to the extended 2D conjugation. Conjugated side chains on the acceptor induce the self-aggregation of the acceptors, while conjugated side chains on the donor increase the miscibility of the donors and acceptors, thus optimizing the morphology of the active layers. The blends based on mixed combinations, namely 1D donor/2D acceptor and 2D donor/1D acceptor, show better performance relative to 1D donor/1D acceptor and 2D donor/2D acceptor. 

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3. Synthesis and Structure‐Property Relationships in Regioisomeric Alternating Borane‐Terthiophene Polymers

   https://doi.org/10.1002/chem.202203619  

   Alahmadi, Abdullah_F; Yin, Xiaodong; Lalancette, Roger_A; Jäkle, Frieder (February 2023, Chemistry – A European Journal)

   Abstract Main‐chain boron‐containing π‐conjugated polymers are attractive for organic electronic, sensing, and imaging applications. Alternating terthiophene‐borane polymers were prepared and the effects of regioisomeric attachment of the conjugated linker and variations in the electronic effect of the pendent aryl groups (2,4,6‐tri‐tert‐butylphenyl, Mes*; 2,4,6‐tris(trifluoromethyl)phenyl, FMes) examined. Pd₂dba₃/P(t‐Bu)₃‐catalyzed Stille polymerization of arylbis(2‐thienyl)borane and arylbis(3‐thienylborane) with 2,5‐bis(trimethylstannyl)thiophene at 120 °C gave polymers with appreciable molecular weight but MALDI‐TOF MS analyses showed evidence of unusually prominent homocoupling. These defects could be suppressed by using brominated rather than iodinated monomers, more hindered 2,5‐bis(tri‐n‐butylstannyl)thiophene as comonomer, and Pd₂dba₃/P(o‐tol)₃as the catalyst at 100 °C. Under these conditions, macrocyclic species withn=3–10 repeating units formed preferentially according to MALDI‐TOF MS analyses. Photophysical studies revealed a prominent effect of the regiochemistry and the nature of the pendent aryl groups on the absorption and emission, giving rise to orange, yellow‐green, blue‐green, and blue emissive materials respectively. The electronic effects were rationalized through DFT calculations on bis(terthiophene) model systems. 

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4. The Effects of Crystallinity on Charge Transport and the Structure of Sequentially Processed F ₄ TCNQ‐Doped Conjugated Polymer Films

   https://doi.org/10.1002/adfm.201702654  

   Scholes, D_Tyler; Yee, Patrick_Y; Lindemuth, Jeffrey_R; Kang, Hyeyeon; Onorato, Jonathan; Ghosh, Raja; Luscombe, Christine_K; Spano, Frank_C; Tolbert, Sarah_H; Schwartz, Benjamin_J (September 2017, Advanced Functional Materials)

   Abstract The properties of molecularly doped films of conjugated polymers are explored as the crystallinity of the polymer is systematically varied. Solution sequential processing (SqP) was used to introduce 2,3,5,6‐tetrafluoro‐7,7,8,8‐tetracyanoquinodimethane (F₄TCNQ) into poly(3‐hexylthiophene‐2,5‐diyl) (P3HT) while preserving the pristine polymer's degree of crystallinity. X‐ray data suggest that F₄TCNQ anions reside primarily in the amorphous regions of the film as well as in the P3HT lamellae between the side chains, but do not π‐stack within the polymer crystallites. Optical spectroscopy shows that the polaron absorption redshifts with increasing polymer crystallinity and increases in cross section. Theoretical modeling suggests that the polaron spectrum is inhomogeneously broadened by the presence of the anions, which reside on average 6–8 Å from the polymer backbone. Electrical measurements show that the conductivity of P3HT films doped by F₄TCNQ via SqP can be improved by increasing the polymer crystallinity. AC magnetic field Hall measurements show that the increased conductivity results from improved mobility of the carriers with increasing crystallinity, reaching over 0.1 cm²V⁻¹s⁻¹in the most crystalline P3HT samples. Temperature‐dependent conductivity measurements show that polaron mobility in SqP‐doped P3HT is still dominated by hopping transport, but that more crystalline samples are on the edge of a transition to diffusive transport at room temperature. 

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5. Tuning the surface energies in a family of poly-3-alkylthiophenes bearing hydrophilic side-chains synthesized via direct arylation polymerization (DArP)

   https://doi.org/10.1039/D1PY00195G  

   Schmitt, Alexander; Samal, Sanket; Thompson, Barry C. (May 2021, Polymer Chemistry)

   null (Ed.)

   Recent work has identified surface energy as a key figure of merit in predicting the morphology of bulk heterojunction organic solar cells and organic alloy formation in ternary blend organic solar cells. An efficient way of tuning surface energy in conjugated polymers is by introducing functionalised side chains. Here, we present a systematic study on a family of poly(3-hexylthiophene) (P3HT)-based random copolymers bearing five different functionalised side chains (ester, ether, diether, carbamate, nitrile) prepared by direct arylation polymerization (DArP) in terms of their effectiveness in tuning surface energy. This study also exemplifies the superior functional group tolerance in DArP compared to more traditional polymerization procedures. Water droplet contact angle measurements revealed that especially carbamates are highly effective in tuning surface energy, increasing the surface energy from 21.2 mN m −1 with P3HT to 25.5 mN m −1 and 28.6 mN m −1 in 25% and 50% carbamate functionalized copolymers, respectively. Importantly, by introducing a two-carbon-spacer between the conjugated backbone and the functional group, optical and electronic properties of P3HT could be largely maintained in the copolymers as determined by UV/Vis, cyclic voltammetry and space charge limited current hole mobility. 

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