Chengjun Pan

Picket-Fence Polythiophene and its Diblock Copolymers that Afford Microphase Separations Comprising a Stacked and an Isolated Polythiophene Ensemble†

All-polythiophene diblock copolymers, comprising one unsheathed block and one fenced block, were synthesized through catalyst-transfer polycondensation. The unsheathed block self-assembles through π-π stacking, thereby inducing microphase separation. Consequently, we have succeeded in creating a microphase separation comprising an ensemble of stacked and isolated polythiophenes. This achievement could be extended to various unexplored applications as a result of the integration of the contrasting functions of the two blocks.

The effect of the backbone structure on the thermoelectric properties of donor–acceptor conjugated polymers

Three donor–acceptor (D–A)-structured conjugated polymers with different backbones, poly((9,9-dioctylfluorene)-2,7-diyl-alt-benzothiadiazole) (F8BT), poly((9,9-dioctylfluorene)-2,7-diyl-alt-(4,7-bis(3-hexylthien-5-yl)-2,1,3-benzothiadiazole)-2′,2′′-diyl) (F8TBT), and poly(N-9′-heptadecanyl-2,7-carbazole-alt-(4,7-bis(3-hexylthien-5-yl)-2,1,3-benzothiadiazole)-2′,2′′-diyl) (C8TBT), were synthesized via conventional Suzuki polymerization. All three polymers showed good thermal and electrochemical stabilities. The UV-vis absorption spectra indicated that the introduction of thiophene units into the polymer backbone decreased the bandgap of the polymers. When the three polymer films were doped with FeCl3, different thermoelectric properties were observed. F8TBT and C8TBT, which contained thiophene units, showed a higher electrical conductivity than F8BT. As the temperature increased, C8TBT exhibited the highest Seebeck coefficient of 335 μV K−1 at 90 °C and a maximum power factor of 13.11 μW m−1 K−2. These results demonstrated that the polymer backbone structure greatly influences the thermoelectric properties and the inclusion of thiophene and carbazole units can effectively improve the thermoelectric properties. Therefore, this work is a novel and important reference to design and synthesize high-performance thermoelectric conjugated polymers.

Side‐Chain Effects on the Thermoelectric Properties of Fluorene‐Based Copolymers

Three conjugated polymers with alkyl chains of different lengths are designed and synthesized, and their structure-property relationship as organic thermoelectric materials is systematically elucidated. All three polymers show similar photophysical properties, thermal properties, and mechanical properties; however, their thermoelectric performance is influenced by the length of their side chains. The length of the alkyl chain significantly influences the electrical conductivity of the conjugated polymers, and polymers with a short alkyl chain exhibit better conductivity than those with a long alkyl chain. The length of the alkyl chain has little effect on the Seebeck coefficient. Only a slight increase in the Seebeck coefficient is observed with the increasing length of the alkyl chain. The purpose of this study is to provide comprehensive insight into fine-tuning the thermoelectric properties of conjugated polymers as a function of side-chain engineering, thereby providing a novel perspective into the design of high-performance thermoelectric conjugated polymers.

Preparation and Characterization of Bi2Te3/Graphite/Polythiophene Thermoelectric Composites

The Bi2Te3/graphite/polythiophene composites were prepared by solution mixing, mechanical ball milling, cold pressing and spark plasma sintering (SPS) in order to utilize and integrate the high Seebeck coefficient of Bi2Te3, high electrical conductivity of graphite (G) and low thermal conductivity of polythiophene (PTh). The structures and properties of the composites were characterized by scanning electron microscope, thermo gravimetric analyzer, x-ray diffraction and ULVAC ZEM-2 Seebeck coefficient measurement. The results showed that the related components were uniformly dispersed in the composites, and the electrical conductivity of the composites increased significantly with increasing G content. A small addition of Bi2Te3 to the matrix contributed to an increase in Seebeck coefficient and the thermal conductivity of the composites stayed at a low level owing to the low thermal conductivity of PTh. These composites prepared by SPS show an increase in Seebeck coefficient but a decrease in electrical conductivity as compared to corresponding composites prepared by cold pressing.Graphical Abstract

Polymer chain alignment and transistor properties of nanochannel-templated poly(3-hexylthiophene) nanowires

Nanowires of semiconducting poly(3-hexylthiophene) (P3HT) were produced by a nanochannel-template technique. Polymer chain alignment in P3HT nanowires was investigated as a function of nanochannel widths (W) and polymer chain lengths (L). We found that the ratio between chain length and channel width (L/W) was a key parameter as regards promoting polymer chain alignment. Clear dichroism was observed in polarized ultraviolet-visible (UV-Vis) absorption spectra only at a ratio of approximately L/W = 2, indicating that the L/W ratio must be optimized to achieve uniaxial chain alignment in the nanochannel direction. We speculate that an appropriate L/W ratio is effective in confining the geometries and conformations of polymer chains. This discussion was supported by theoretical simulations based on molecular dynamics. That is, the geometry of the polymer chains, including the distance and tilting angles of the chains in relation to the nanochannel surface, was dominant in determining the longitudinal alignme...

A study of the thermoelectric properties of benzo[1,2-b:4,5-b′]dithiophene–based donor–acceptor conjugated polymers

Three benzo[1,2-b:4,5-b′]dithiophene (BDT)-based donor–acceptor (D–A) conjugated polymers with different side chains were designed, synthesized, and investigated as organic thermoelectric materials. Changing the side chains caused the three polymers to have different physical and chemical properties. The thermoelectric properties of BDT-based conjugated polymers have been systematically investigated through fine tuning of the side chains. Among the three polymers, the polymer with alkylthienothiophene moieties as the side chains exhibited the best thermal stability (thermal decomposition temperature above 400 °C), the highest electrical conductivity (1.519 S cm−1), and the largest Seebeck coefficient (413.79 μV K−1). The results of this study can guide the future design and synthesis of high-performance thermoelectric conjugated polymers.

High-performance n-type thermoelectric composites of acridones with tethered tertiary amines and carbon nanotubes

Very recently, amino-substituted perylene diimides (PDINE) and naphthalene diimides (NDINE) have been reported as good n-type thermoelectric (TE) materials; rational design of their derivatives is strongly desired to further enhance their TE performance. In this study, based on the molecular structure of PDINE and NDINE, a series of acridones with different terminal tertiary amine groups (ADTA) at the C2 and/or C7 positions of the acridone ring was designed and synthesised as potential n-type TE materials. Then, single-walled carbon nanotubes (SWCNTs) were combined with the acridones to form flexible SWCNT/ADTA composite films. The composites exhibited excellent n-type TE performance. Furthermore, the terminal tertiary amine and the number of side chains greatly affected the TE properties of the composites. The composite containing an acridone with two terminal diethyl amine groups displayed the highest power factor of 289.4 ± 2.8 μW m−1 K−2 at 430 K, which is perhaps one of the highest values reported to date for a composite containing n-type small organic molecules and SWCNTs. In addition, the composite with a functionalised piperidine acridone displayed p-type TE behaviour with a high power factor of 211.6 ± 9.9 μW m−1 K−2 at room temperature. Our results demonstrate that SWCNT/acridone composites with appropriate substituents show promise as TE materials, which opens a new avenue for TE material design.