Hoyoul Kong

New selenophene-based semiconducting copolymers for high performance organic thin-film transistors

A series of new selenophene-based organic semiconducting copolymers, poly(5,5′-bis(3-dodecylthiophen-2-yl)-2,2′-biselenophene) (PDT2Se2) and poly(5,5′-bis(4,4′-didodecyl-2,2′-bithiophen-5-yl)-2,2′-biselenophene) (PDT4Se2), were successfully synthesized by Stille and oxidative coupling reactions. Our aim was to investigate the effects of the selenophene units and inserted dodecylthiophenes on the optical and electrochemical properties of these copolymers, their intermolecular ordering in the film state, and hence their thin-film transistor (TFT) performance. X-ray-diffraction (GIXRD and XRD) and theoretical calculations for models of these polymers were used to show that PDT2Se2 films have well organized interlayer packing and π–π stacking, whereas the films of PDT4Se2, which contain regioregularly inserted additional dodecylthiophenes next to the repeat units of PDT2Se2, have a long-range amorphous structure. The TFT characteristics of these polymers are strongly dependent on the intermolecular ordering of the polymer chains. PDT2Se2 exhibited a high hole transporting mobility of 0.02 cm2V−1 s−1 due to its excellent intermolecular ordering, whereas PDT4Se2 exhibited a very poor mobility of 1.4 × 10−5 cm2V−1 s−1 due to its amorphous characteristics, which result from the repulsion between the additional dodecylthiophenes. These results confirm that it is important to consider intermolecular ordering in the design of semiconducting materials for high performance OTFTs.

New amorphous semiconducting copolymers containing fluorene and thiophene moieties for organic thin-film transistors

New amorphous semiconducting materials consisting of fluorene-based thiophene copolymers, poly(2-(5-(9,9-dibutyl-9 H-fluoren-2-yl)-3-hexylthiophen-2-yl)-5-(3-hexylthiophen-2-yl)thieno[3,2-b]thiophene) P1 and poly(2-(5-(9,9-dibutyl-9 H-fluoren-2-yl)-4-hexylthiophen-2-yl)-5-(4-hexylthiophen-2-yl)thieno[3,2-b]thiophene) P2, have been successfully synthesized via a palladium-catalyzed Suzuki coupling reaction. The number-average molecular weights (Mn) of P1 and P2 were found to be 18 300, and 15 800, respectively. These polymers dissolve in common organic solvents such as chloroform, chlorobenzene, and toluene. The UV-vis absorption maxima of P1 and P2 appeared at 436 and 427 nm in solution and 441 and 431 nm in the film state, respectively. X-Ray diffraction (XRD) analysis showed no reflection peaks indicating amorphous collections of randomly oriented polymer chains. Atomic force microscopy (AFM) images of P1 and P2 showed amorphous film morphologies. Field-effect transistor mobilities of stable amorphous OTFTs of P1 and P2 under ambient conditions have been achieved up to 5.4 × 10−4 cm2V−1 s−1 and 1.6 × 10−4 cm2V−1 s−1, respectively. The high stability and mobility of fluorene-based thiophene copolymers in the amorphous state make them a new family of promising candidates for organic thin-film transistors.

Thermal annealing induced bicontinuous networks in bulk heterojunction solar cells and bipolar field-effect transistors

Polymer bulk heterojunction solar cells fabricated from poly(2,5-bis(3′-dodecyl-2,2′-bithiophen-5-yl)-3,6-dimethylthieno [3,2-b] thiophene):[6,6]-phenyl-C61-butric acid methyl ester (1:1, w/w) blend showed significantly improved power conversion efficiency (PCE), from 0.96% to 2.32%, with post-thermal annealing at 140 °C. Charge transport properties obtained from bipolar field-effect transistors indicated that post-thermal annealing induced the assembly of significantly improved bicontinuous networks and excellently balanced hole (7.2×10−3 cm2 V−1 s−1) and electron (5.8×10−3 cm2 V−1 s−1) mobilities (due, particularly, to improved electron mobility), thereby improving PCE.

Synthesis and Properties of Fluorinated Styrene Copolymers as Antibiofouling Coatings

A series of polystyrene (PS) copolymers containing 2,3,4,5,6-pentafluorostyrene units with different monomer ratios were prepared for antifouling applications. PS, poly(styrene-co-pentafluorostyrene) (poly(S-co-FS)), and poly(pentafluorostyrene) (PFS) were synthesized by free-radical polymerization and characterized by 1H NMR, Fourier-transform infrared spectroscopy, and gel permeation chromatography. The surface energy of the polymer films decreased with increasing content of fluorinated styrene. Protein adsorption experiments were carried out on the synthesized polymer films using fluorescein isothiocyanate-labeled bovine serum albumin as a fluorescent protein. The photo-luminescence intensity of the protein-adsorbed polymer films decreased dramatically as the content of hydrophobic fluorinated styrene increased, suggesting that poly(S-co-FS) copolymers and PFS could be used as potential antibiofouling coatings.

A metal-ion-chelating organogel electrolyte for Le Chatelier depression of Mn3+ disproportionation of lithium manganese oxide spinel

We present a metal-ion-chelating organogel electrolyte, thermally gelated within cells, to solve the problems triggered by metal dissolution from cathodes of lithium ion batteries. The organogel significantly improved the capacity retention of lithium manganese oxide spinel during cycling. The organogel mitigated metal deposition on anodes by capturing metal ions (anode protection). Interestingly, the organogel inhibited metal dissolution by keeping dissolved metal ions highly concentrated around the cathode surface (cathode protection by Le Chateliers principle).