Songting Tan

Multiferroic CoFe2O4–Pb(Zr0.52Ti0.48)O3 nanofibers by electrospinning

Multiferroic materials possess two or more types of orders simultaneously that couple the electric and magnetic fields, and composite multiferroics have been widely explored for their excellent magnetoelectric coupling. In this letter, we report a strategy to hybrid multiferroicity at nanoscale. Multiferroic CoFe2O4–Pb(Zr0.52Ti0.48)O3 nanofibers are synthesized by sol-gel process and electrospinning, the spinel structure of CoFe2O4 (CFO) and perovskite structure of Pb(Zr0.52Ti0.48)O3 (PZT) are verified by x-ray diffraction and high resolution transmission electron microscopy, and the multiferroicity of the nanofibers are confirmed by piezoresponse force microscopy and magnetic hysteresis. Excellent ferroelectric and ferromagnetic properties have been observed, which could enable multiferroic devices at nanoscale.

Co-sensitized DSCs: dye selection criteria for optimized device Voc and efficiency

Co-sensitization of nanocrystalline TiO2 with the organic dye D2 and the zinc phthalocyanine dye TT1 improves light harvesting, Jsc and efficiency of DSC devices. However, the Voc of the co-sensitized cell is markedly inferior (∼130 mV) when compared to the reference device made with D2 only. We discuss the implications of our results with regard to selection criteria for dyes for co-sensitized DSCs.

High‐Performance, Air‐Stable Field‐Effect Transistors Based on Heteroatom‐Substituted Naphthalenediimide‐Benzothiadiazole Copolymers Exhibiting Ultrahigh Electron Mobility up to 8.5 cm V−1 s−1

Rational heteroatom engineering is applied to develop high-performance electron-transporting naphthalenediimide copolymers. Top-gate field-effect transistors fabricated from selenophene-containing polymers achieve an ultrahigh electron mobility of 8.5 cm2 V-1 s-1 and excellent air-stability. The results demonstrate that the incorporation of selenophene heterocycles into the polymers can improve the film-forming ability, intermolecular interaction, and carrier transport significantly.

Synthesis and photovoltaic properties of polythiophene stars with porphyrin core

Two novel porphyrin-polythiophene star-shaped polymer (P-bs1 and P-bs2) containing triphenylamine terminated poly(3′-hexyl-2,2′-bithiophene) and poly(3′-hexyl-2,2′-bithiophene) as four arms in the peripheral of porphyrin core were synthesized by Stille reaction. The thermal, photophysical, electrochemical and photovoltaic properties of the porphyrin-polythiophene derivatives were investigated. The porphyrin-polythiophene derivatives showed broad absorption in the region of 350 ∼ 650 nm. In particular, the absorption intensity at 450 ∼ 650 nm was greatly enhanced for the meso-substituted polythiophene derivatives, P-bs2. The photoluminescence spectra indicated that the emission peaks of porphyrin units were suppressed by the intensive emission of thiophene units. The electrochemical properties indicated that the porphyrin-polythiophene derivatives are potential electron-donor materials for bulk heterojunction solar cells and dye-sensitized solar cells (DSSCs). Polymer bulk heterojunction solar cells based on P-bs2:PCBM (1:1, w/w) showed power conversion efficiencies (PCE) up to 0.61% under the illumination of AM 1.5, 100 mW cm−2, which increased by 69% compared to that of P-bs1 (0.36%). Meanwhile, higher PCE of 2.17% and 3.91% based on P-bs1 and P-bs2 polymer-sensitized solar cells were attained. The better photovoltaic properties benefited from longer arms of polythiophene derivatives.

Efficient polymer solar cells based on terpolymers with a broad absorption range of 300–900 nm

Three novel random conjugated terpolymers were designed and synthesized by copolymerizing a benzo[1,2-b:4,5-b′]dithiophene (BDT) donor with an electron-deficient diketopyrrolo[3,4-c]pyrrole (DPP) unit and a thiophene-vinylene-dithienyl-benzothiadiazole (TVDTBT) side group into a polymer backbone. By tuning the ratio of DPP and TVDTBT in the terpolymers, the optical properties and energy levels of these random terpolymers could be rationally controlled. As a result, the terpolymers exhibited a very broad absorption range of 300–900 nm with a high absorption coefficient and deep HOMO energy levels. Bulk heterojunction polymer solar cells fabricated from P3 and PC61BM exhibited a promising power conversion efficiency of 5.29% without any processing additives.

Synthesis and photovoltaic performances of conjugated copolymers with 4,7-dithien-5-yl-2,1,3-benzothiadiazole and di(p-tolyl)phenylamine side groups

Three new copolymers (PT-TPA, PT-DTBT and PT-DTBTTPA) based on benzo[1,2-b:4,5-b]dithiophene (BDT) and thiophene with different conjugated side chains (di(p-tolyl)phenylamine (TPA), 4,7-dithien-5-yl-2,1,3-benzothiadiazole (DTBT) and DTBT-TPA) were synthesized via Stille coupling polymerization. The TPA and the DTBT were introduced to improve the hole-transport ability and broaden the absorption spectrum. The effects of different conjugated side groups on thermal, optical, electrochemical, hole-transporting and photovoltaic properties of these copolymers were investigated. Field effect results show that the copolymer PT-DTBTTPA containing TPA and DTBT in the side chain showed the highest hole mobility. The three copolymers exhibit deep-lying HOMO energy levels, which were effectively tuned by changing the side groups. Photovoltaic cells were fabricated with the synthesized copolymers as electron donors and [6,6]-phenyl-C-butyric acid methyl ester (PCBM) as the electron acceptor. Bulk heterojunction polymer solar cells based on PT-DTBT and PT-DTBTTPA showed promising power conversion efficiencies of 5.50% and 5.16%, respectively.

Improved photovoltaic properties of terpolymers containing diketopyrrolopyrrole and an isoindigo side chain

A series of donor–acceptor (D–A) conjugated random terpolymers were synthesized by copolymerizing electron-rich alkylthienyl-substituted benzodithiophene (BDTT) and two electron-deficient units, a diketopyrrolopyrrole (DPP) moiety and isoindigo (TID) based side chain. The effects of the DPP and TID units on the thermal, photophysical and electrochemical properties of the polymers were investigated using thermogravimetric analysis, UV-vis-NIR absorption spectra, and cyclic voltammetry. Compared with the parent polymers (P1 and P2), the optical properties of the random terpolymers (P3–P6) were controlled successfully by tuning the ratio of DPP and TID. The increase in TID content induced an increased absorption between 450 and 600 nm and a lower highest occupied molecular orbital (HOMO) energy level, while higher DPP content resulted in stronger absorption between 600 and 900 nm. Bulk heterojunction solar cells based on the as-synthesized polymers as electron donors and (6,6)-phenyl-C-butyric acid methyl ester (PCBM) as the acceptor were fabricated. The best power conversion efficiency (PCE) of 5.62% was obtained from P5 (DPP : TID = 1 : 1) due to its high short-circuit current density (Jsc higher than 15 mA cm−2), mainly arising from the broadened light absorption. The results have demonstrated that the random terpolymers, with complementary light-absorption, have a great potential for increasing the photocurrent and PCE in polymer solar cells.

Directed metalation cascade to access highly functionalized thieno[2,3-f]benzofuran and exploration as building blocks for organic electronics.

A tandem directed metalation has been successfully applied to the preparation of thieno[2,3-f]benzofuran-4,8-dione, providing an efficient and facile approach to symmetrically and unsymmetrically functionalize the thieno[2,3-f]benzofuran core at the 2,6 positions as well as to introduce the electron-withdrawing or -donating groups (EWG or EDG) at its 4,8 positions. The presence of various functional groups makes late-stage derivatization attainable.

Synthesis, characterization, and field-effect transistor properties of tetrathienoanthracene-based copolymers using a two-dimensional π-conjugation extension strategy: a potential building block for high-mobility polymer semiconductors

In most instances, modulation of the π-conjugation length in polymer molecules is obtained through a linear (1D) extension of the polymer backbone. To date, very limited studies have been reported about the effect of the two-dimensional (2D) π-conjugation extension on the charge-transporting properties of polymer semiconductors. In this study, a 2D π-extended heteroacene, alkyl-substituted tetrathienoanthracene (TTB) moiety, is used to design and synthesize a class of novel polymer semiconductors for solution-processable organic field-effect transistor (OFET) applications for the first time. Three novel TTB-based alternating copolymers (PTTB-2T, PTTB-TT, and PTTB-BZ) are synthesized via Pd(0)-catalyzed Stille or Suzuki cross-coupling reactions, affording high weight-average molecular weights of 61.1–78.5 kDa. The thermal stabilities, optical properties, and energy levels, and charge transport properties of the three TTB-based alternating copolymers have been successfully tuned by copolymerization with bithiophene (2T), thienothiophene (TT), and benzothiadiazole (BZ) derivatives. The results indicate that, even with their highly extended π-framework, all the TTB-containing polymers show good solubility in most common solvents and fairly good environmental stability of their highest occupied molecular orbitals (HOMOs) ranging from −5.15 to −5.28 eV. Among the three TTB-based alternating copolymers, the PTTB-BZ thin film exhibits the best OFET performance with the highest hole mobility of 0.15 cm2 V−1 s−1 in ambient air. It can be attributed to the combinations of highly coplanar polymer backbones and strong D–A interactions between TTB donor units and BZ acceptor units, therefore leading to a compact solid-state packing, uniform fiber-like morphology, and a large polycrystalline grain associated with high hole mobility. These results demonstrate that our molecular design strategy for high-performance polymer semiconductors is highly promising.

Synergetic Effect of Efficient Energy Transfer and 3D π−π Stack for White Emission Based on the Block Copolymers Containing Nonconjugated Spacer

A series of block copolymers containing nonconjugated spacer and 3D pi-pi stacking structure with simultaneous blue-, green-, and yellow-emitting units has been synthesized and characterized. The dependence of the energy transfer and electroluminescence (EL) properties of these block copolymers on the contents of oligo(phenylenevinylene)s has been investigated. The block copolymer (GEO8-BEO-YEO4) with 98.8% blue-emitting oligomer (BEO), 0.8% green-emitting oligomer (GEO), and 0.4% yellow-emitting oligomer (YEO) showed the best electroluminescent performance, exhibiting a maximum luminance of 2309 cd/m(2) and efficiency of 0.34 cd/A. The single-layer-polymer light-emitting diodes device based on GEO2-BEO-YEO4 emitted greenish white light with the CIE coordinates of (0.26, 0.37) at 10 V. The synergetic effect of the efficient energy transfer and 3D pi-pi stack of these block copolymers on the photoluminescent and electroluminescent properties are investigated.