Synergistic Interactions in Sequential Process Doping of Polymer/Single-Walled Carbon Nanotube Nanocomposites for Enhanced n-Type Thermoelectric Performance.

This study focuses on the fabrication of nanocomposite thermoelectric devices by blending either a naphthalene-diimide (NDI)-based conjugated polymer (NDI-T1 or NDI-T2), or an isoindigo (IID)-based conjugated polymer (IID-T2), with single-walled carbon nanotubes (SWCNTs). This is followed by sequential process doping method with the small molecule 4-(2,3-dihydro-1,3-dimethyl-1H-benzimidazol-2-yl)-N,N-dimethylbenzenamine (N-DMBI) to provide the nanocomposite with n-type thermoelectric properties. Experiments in which the concentrations of the N-DMBI dopant are varied demonstrate the successful conversion of all three polymer/SWCNT nanocomposites from p-type to n-type behavior. Comprehensive spectroscopic, microstructural, and morphological analyses of the pristine polymers and the various N-DMBI-doped polymer/SWCNT nanocomposites are performed in order to gain insights into the effects of various interactions between the polymers and SWCNTs on the doping outcomes. Among the obtained nanocomposites, the NDI-T1/SWCNT exhibits the highest n-type Seebeck coefficient and power factor of -57.7 µV K-1 and 240.6 µW m-1 K-2 , respectively. However, because the undoped NDI-T2/SWCNT exhibits a slightly higher p-type performance, an integral p-n thermoelectric generator is fabricated using the doped and undoped NDI-T2/SWCNT nanocomposite. This device is shown to provide an output power of 27.2 nW at a temperature difference of 20 K.

A pH-Sensitive Stretchable Zwitterionic Hydrogel with Bipolar Thermoelectricity.

Amid growing interest in using body heat for electricity in wearables, creating stretchable devices poses a major challenge. Herein, a hydrogel composed of two core constituents, namely the negatively-charged 2-acrylamido-2-methylpropanesulfonic acid and the zwitterionic (ZI) sulfobetaine acrylamide, is engineered into a double-network hydrogel. This results in a significant enhancement in mechanical properties, with tensile stress and strain of up to 470.3 kPa and 106.6%, respectively. Moreover, the ZI nature of the polymer enables the fabrication of a device with polar thermoelectric properties by modulating the pH. Thus, the ionic Seebeck coefficient (Si) of the ZI hydrogel ranges from -32.6 to 31.7 mV K-1 as the pH is varied from 1 to 14, giving substantial figure of merit (ZTi) values of 3.8 and 3.6, respectively. Moreover, a prototype stretchable ionic thermoelectric supercapacitor incorporating the ZI hydrogel exhibits notable power densities of 1.8 and 0.9 mW m-2 at pH 1 and 14, respectively. Thus, the present work paves the way for the utilization of pH-sensitive, stretchable ZI hydrogels for thermoelectric applications, with a specific focus on harvesting low-grade waste heat within the temperature range of 25-40 °C.

Intrinsically Stretchable Organic Thermoelectric Polymers Enabled by Incorporating Fused-Ring Conjugated Breakers.

While research on organic thermoelectric polymers is making significant progress in recent years, realization of a single polymer material possessing both thermoelectric properties and stretchability for the next generation of self-powered wearable electronics is a challenging task and remains an area yet to be explored. A new molecular engineering concept of "conjugated breaker" is employed to impart stretchability to a highly crystalline diketopyrrolepyrrole (DPP)-based polymer. A hexacyclic diindenothieno[2,3-b]thiophene (DITT) unit, with two 4-octyloxyphenyl groups substituted at the tetrahedral sp3-carbon bridges, is selected to function as the conjugated breaker that can sterically hinder intermolecular packing to reduce polymers' crystallinity. A series of donor-acceptor random copolymers is thus developed via polymerizing the crystalline DPP units with the DITT conjugated breakers. By controlling the monomeric DPP/DITT ratios, DITT30 reaches the optimal balance of crystalline/amorphous regions, exhibiting an exceptional power factor (PF) value up to 12.5 µW m-1 K-2 after FeCl3-doping; while, simultaneously displaying the capability to withstand strains exceeding 100%. More significantly, the doped DITT30 film possesses excellent mechanical endurance, retaining 80% of its initial PF value after 200 cycles of stretching/releasing at a strain of 50%. This research marks a pioneering achievement in creating intrinsically stretchable polymers with exceptional thermoelectric properties.

Visible-Light-Promoted Radical Cascade Cyclization of 2-Vinyl Benzimidazoles: Access to Benzo[4,5]imidazo[1,2-b]isoquinolin- 11(6H)-ones.

A visible-light-enabled photoredox radical cascade cyclization of 2-vinyl benzimidazole derivatives is developed. This chemistry is applicable to a wide range of N-aroyl 2-vinyl benzimidazoles as acceptors, and halo compounds, including alkyl halides, acyl chlorides and sulfonyl chlorides, as radical precursors. The Langlois reagent also serves as an effective partner in this photocatalytic oxidative cascade process. This protocol provides a robust alternative for rendering highly functionalized benzo[4,5]imidazo[1,2-b]isoquinolin-11(6H)-ones.

Functionalized Thienopyrazines on NiOx Film as Self-Assembled Monolayer for Efficient Tin-Perovskite Solar Cells Using a Two-Step Method.

Three functionalized thienopyrazines (TPs), TP-MN (1), TP-CA (2), and TPT-MN (3) were designed and synthesized as self-assembled monolayers (SAMs) deposited on the NiOx film for tin-perovskite solar cells (TPSCs). Thermal, optical, electrochemical, morphological, crystallinity, hole mobility, and charge recombination properties, as well as DFT-derived energy levels with electrostatic surface potential mapping of these SAMs, have been thoroughly investigated and discussed. The structure of the TP-MN (1) single crystal was successfully grown and analyzed to support the uniform SAM produced on the ITO/NiOx substrate. When we used NiOx as HTM in TPSC, the device showed poor performance. To improve the efficiency of TPSC, we utilized a combination of new organic SAMs with NiOx HTM, the TPSC device exhibited the highest PCE of 7.7% for TP-MN (1). Hence, the designed NiOx/TP-MN (1) acts as a new model system for the development of efficient SAM-based TPSC. To the best of our knowledge, the combination of organic SAMs with anchoring CN/CN or CN/COOH groups, and NiOx HTM for TPSC has never been reported elsewhere. The TPSC device based on the NiOx/TP-MN bilayer exhibits great enduring stability for performance, retaining ~80% of its original value for shelf storage over 4000 h.

Efficiency improvement of inverted perovskite solar cells enabled by PTAA/MoS2double hole transporters.

Hole transport layer (HTL) plays a critical role in perovskite solar cells (PSCs). We focus on the improvement of PSCs performance with MoS2nanosheets as the anode buffer layer in the inverted photovoltaic structure. PSC with single MoS2buffer layer shows poor performance in power conversion efficiency (PCE) and the long-term stability. By combination of MoS2and Poly[bis(4-phenyl) (2,4,6-trimethylphenyl) amine] (PTAA) as double-layer HTL, the PCE is improved to 18.47%, while the control device with PTAA alone shows a PCE of 14.48%. The same phenomenon is also found in 2D PSCs. For double-layer HTL devices, the PCE reaches 13.19%, and the corresponding PCE of the control group using PTAA alone is 10.13%. This significant improvement is attributed to the reduced interface resistance and improved hole extraction ability as shown by the electric impedance spectroscopy and fluorescence spectroscopy. In addition, the improved device exhibits better stability because the PCE still maintains 66% of the initial value after 500 h of storage, which is higher than the 47% of the remaining PCE from device based on single PTAA or MoS2. Our results demonstrate the potential of polymer/inorganic nanomaterial as a double-layer buffer material for PSCs.

Nano-Micro Dimensional Structures of Fiber-Shaped Luminous Halide Perovskite Composites for Photonic and Optoelectronic Applications.

Perovskite nanomaterials have been revealed as highly luminescent structures regarding their dimensional confinement. In particular, their promising potential lies behind remarkable luminescent properties, including color tunability, high photoluminescence quantum yield, and the narrow emission band of halide perovskite (HP) nanostructures for optoelectronic and photonic applications such as lightning and displaying operations. However, HP nanomaterials possess such drawbacks, including oxygen, moisture, temperature, or UV lights, which limit their practical applications. Recently, HP-containing polymer composite fibers have gained much attention owing to the spatial distribution and alignment of HPs with high mechanical strength and ambient stability in addition to their remarkable optical properties comparable to that of nanocrystals. In this review, the fabrication methods for preparing nano-microdimensional HP composite fiber structures are described. Various advantages of the luminescent composite nanofibers are also described, followed by their applications for photonic and optoelectronic devices including sensors, polarizers, waveguides, lasers, light-down converters, light-emitting diode operations, etc. Finally, future directions and remaining challenges of HP-based nanofibers are presented.

Performance of DWI as a Rapid Unenhanced Technique for Detecting Mammographically Occult Breast Cancer in Elevated-Risk Women With Dense Breasts.

OBJECTIVE: The objective of our study was to evaluate the performance of DWI to detect mammographically occult breast cancer in elevated-risk women with dense breasts. MATERIALS AND METHODS: We retrospectively reviewed all women who underwent screening breast MRI at our institution from January 2007 through May 2013. We created a case-control cohort composed of 48 subjects with mammographically dense breasts: 24 with mammographically occult cancer detected on MRI and 24 healthy women with negative MRI findings who were matched to the subjects with breast cancer patients for age, breast density, and MRI protocol. The contrast-to-noise ratio (CNR), apparent diffusion coefficient (ADC), and conspicuity score (range, 1-5) were assessed on DWI for all malignancies. Lesions and normal tissue were compared using the Wilcoxon signed rank test; associations with clinical characteristics were evaluated using the Mann-Whitney U test. Three experienced breast imagers who were blinded to medical records and contrast-enhanced MRI findings independently evaluated the unenhanced MRI scans of the 48 women for the presence of cancer. RESULTS: Mammographically occult breast cancers (invasive carcinoma, n = 16; ductal carcinoma in situ, n = 8) in women with dense breasts typically exhibited higher signal intensity on DWI than normal parenchyma (median CNR of cancers, 1.4; median conspicuity score of cancers, 4) and a lower ADC (median, 1.31 vs 1.79 × 10(-3) mm(2)/s, respectively) (p < 0.0001). The conspicuity score, CNR, and ADC were not associated with patient age, menopausal status, lesion size, morphologic type, or histology (p > 0.05). Average reader performance using unenhanced MRI was 45% sensitivity, 91% specificity, 62% positive predictive value, and 83% negative predictive value. CONCLUSION: In elevated-risk women with dense breasts, DWI can reveal cancers in addition to those detected on mammography alone with a low false-positive rate; these results suggest that DWI may have potential as a rapid supplemental screening tool.

Tumor-induced alterations in lymph node lymph drainage identified by contrast-enhanced MRI.

BACKGROUND: To use high resolution MRI lymphography to characterize altered tumor-draining lymph node (TDLN) lymph drainage in response to growth of aggressive tumors. METHODS: Six mice bearing B16-F10 melanomas in one rear footpad were imaged by 3.0 Tesla (T) MRI before and after subcutaneous injection of Gadofosveset trisodium (Gd-FVT) contrast agent into both rear feet. Gd-FVT uptake into the left and right draining popliteal LNs was quantified and compared using Wilcoxon signed-rank test. Fluorescent dextran lymphography compared patterns of LN lymph drainage with the pattern of immunostained lymphatic sinuses by fluorescence microscopy. RESULTS: TDLNs exhibited greater Gd-FVT uptake than contralateral uninvolved LNs, although this difference did not reach significance (P < 0.06). Foci of contrast agent consistently surrounded the medulla and cortex of TDLNs, while Gd-FVT preferentially accumulated in the cortex of contralateral LNs at 5 and 15 min after injection. Fluorescent dextran lymphography confirmed these distinct contrast agent uptake patterns, which correlated with lymphatic sinus growth in TDLNs. CONCLUSION: 3.0T MRI lymphography using Gd-FVT identified several distinctive alterations in the uptake of contrast agent into TDLNs, which could be useful to identify the correct TDLN, and to characterize TDLN lymphatic sinus growth that may predict metastatic potential.

Diffusion-weighted imaging: Effects of intravascular contrast agents on apparent diffusion coefficient measures of breast malignancies at 3 Tesla.

BACKGROUND: To determine whether apparent diffusion coefficient (ADC) measures of breast lesions at 3 Tesla (T) are affected by gadolinium administration. METHODS: The study included 19 patients who underwent 3T MRI. Diffusion-weighted imaging (DWI) was acquired with b = 0, 100, and 800 s/mm(2) before and after a dynamic contrast-enhanced (DCE) sequence. ADC values were measured for each lesion and normal fibroglandular tissue. Pre- and postcontrast ADC measures were compared by Wilcoxon signed-rank test, and differences between groups were compared by Mann-Whitney U test; P < 0.05 was considered statistically significant. RESULTS: There was no significant difference in pre- and postcontrast ADC measured at b = 0, 100, 800 s/mm(2) for malignancies (median change: -0.4%, -0.01 × 10(-3) mm(2) /s, P = 0.40), but there was a slight increase in postcontrast ADC in normal tissue (+1.6%, +0.04 × 10(-3) mm(2) /s, P = 0.0006). Findings were similar for both lesions (-0.4%, -0.01 × 10(-3) mm(2) /s, P = 0.54) and normal tissue (+1.5%, +0.03 × 10(-3) mm(2) /s, P = 0.002) with ADC measured at b = 0,800 and also at b = 100, 800 s/mm(2) (lesions: +0.9%, +0.01 × 10(-3) mm(2) /s, P = 0.71; normal tissue: +1.8%, +0.03 × 10(-3) mm(2) /s, P = 0.005). For lesions, results were not affected by lesion size, type (mass versus nonmass enhancement), mean initial enhancement, late enhancement, or delayed enhancement rate on DCE-MRI (P > 0.05 for all). Normal tissue showed some trends with greater progressive enhancement rates and higher late enhancement levels correlating with greater increase in postcontrast ADC (P = 0.09 for both). CONCLUSION: Our results show that breast lesion ADC measures using our approach were not significantly altered following DCE-MRI at 3T, suggesting DWI and DCE-MRI can be performed in any order without affecting diagnostic criteria. However, influences of contrast on ADC measures in normal breast tissue were observed and require further investigation.

[Detection of slight bruises on apples based on hyperspectral imaging and MNF transform].

Bruising is one of the major defects occurring on apple surface inevitably during postharvest handling and processing stage. To detect slight bruises on apples fast and efficiently, a novel bruises detection algorithm based on hyperspectral imaging and minimum noise fraction transform is proposed. First, the hyperspectral images in the visible and near-infrared (400 approximately 1 000 nm) ranges are acquired, and MNF transform based on full ranges could obtain better detection performance compared to PCA transform; Second, five wavebands (560, 660, 720, 820 and 960 nm) are selected as the effective wavebands based on the coefficient curve of I-RELIEF method conducted on spectra extracted from intact and bruise surface; Third, the bruises detection algorithm is developed based on the effective wavebands and MNF transform method. For the investigated 40 sound samples and 40 different time stage bruise samples, the results with a 97. 1% overall detection rate are got. The recognition results indicate that the proposed methods and the effective wavelengths selected in this paper are feasible and efficient. This research lays a foundation for the development of multispectral imaging system based on MNF transform for slight bruises detection on apples.

Enhanced Electrical Conductivity and Mechanical Properties of Stretchable Thermoelectric Generators Formed by Doped Semiconducting Polymer/Elastomer Blends.

Recent research efforts have concentrated on the development of flexible and stretchable thermoelectric (TE) materials. However, significant challenges have emerged, including increased resistance and reduced electrical conductivity when subjected to strain. To address these issues, rigid semiconducting polymers and elastic insulating polymers have been incorporated and nanoconfinement effects have been exploited to enhance the charge mobility. Herein, a feasible approach is presented for fabricating stretchable TE materials by using a doped semiconducting polymer blend consisting of either poly(3-hexylthiophene) (P3HT) or poly(3,6-dithiophen-2-yl-2,5-di(2-decyltetradecyl)-pyrrolo[3,4-c]pyrrole-1,4-dione-alt-thienylenevinylene-2,5-yl) (PDVT-10) as the rigid polymer with styrene-ethylene-butylene-styrene (SEBS) as the elastic polymer. In particular, the blend composition is optimized to achieve a continuous network structure with SEBS, thereby improving the stretchability. The optimized polymer films exhibit well-ordered microstructural aggregates, indicative of good miscibility with FeCl3 and enhanced doping efficiency. Notably, a lower activation energy and higher charge-carrier concentration contribute to an improved electrical conductivity under high tensile strain, with a maximum output power of 1.39 nW at a ΔT of 22.4 K. These findings offer valuable insights and serve as guidelines for the development of stretchable p-n junction thermoelectric generators based on doped semiconducting polymer blends with potential applications in wearable electronics and energy harvesting.

Diselenophene-Dithioalkylthiophene Based Quinoidal Small Molecules for Ambipolar Organic Field Effect Transistors.

This work presents a series of novel quinoidal organic semiconductors based on diselenophene-dithioalkylthiophene (DSpDST) conjugated cores with various side-chain lengths (-thiohexyl, -thiodecyl, and -thiotetradecyl, designated DSpDSTQ-6, DSpDSTQ-10, and DSpDSTQ-14, respectively). The purpose of this research is to develop solution-processable organic semiconductors using dicyanomethylene end-capped organic small molecules for organic field effect transistors (OFETs) application. The physical, electrochemical, and electrical properties of these new DSpDSTQs are systematically studied, along with their performance in OFETs and thin film morphologies. Additionally, the molecular structures of DSpDSTQ are determined through density functional theory (DFT) calculations and single-crystal X-ray diffraction analysis. The results reveal the presence of intramolecular S (alkyl)···Se (selenophene) interactions, which result in a planar SR-containing DSpDSTQ core, thereby promoting extended π-orbital interactions and efficient charge transport in the OFETs. Moreover, the influence of thioalkyl side chain length on surface morphologies and microstructures is investigated. Remarkably, the compound with the shortest thioalkyl chain, DSpDSTQ-6, demonstrates ambipolar carrier transport with the highest electron and hole mobilities of 0.334 and 0.463 cm2 V-1 s-1 , respectively. These findings highlight the excellence of ambipolar characteristics of solution-processable OFETs based on DSpDSTQs even under ambient conditions.

Electrical Double-Layer Transistors Comprising Block Copolymer Electrolytes for Low-Power-Consumption Photodetectors.

Electrical double-layer transistors (EDLTs) have received extensive research attention owing to their exciting advantages of low working voltage, high biocompatibility, and sensitive interfacial properties in ultrasensitive portable sensing applications. Therefore, it is of great interest to reduce photodetectors' operating voltage and power consumption by utilizing photo-EDLT. In this study, a series of block copolymers (BCPs) of poly(4-vinylpyridine)-block-poly(ethylene oxide) (P4VP-b-PEO) with different compositions were applied to formulate polyelectrolyte with indigo carmine salt in EDLT. Accordingly, PEO conduces ion conduction in the BCP electrolyte and enhances the carrier transport capability in the semiconducting channel; P4VP boosts the photocurrent by providing charge-trapping sites during light illumination. In addition, the severe aggregation of PEO is mitigated by forming a BCP structure with P4VP, enhancing the stability and photoresponse of the photo-EDLT. By optimizing the BCP composition, EDLT comprising P4VP16k-b-PEO5k and indigo carmine provides the highest specific detectivity of 2.1 × 107 Jones, along with ultralow power consumptions of 0.59 nW under 450 nm light illumination and 0.32 pW under dark state. The results indicate that photo-EDLT comprising the BCP electrolyte is a practical approach to reducing phototransistors' operating voltage and power consumption.

Reversible Molecular Conformation Transitions of Smectic Liquid Crystals for Light/Bias-Gated Transistor Memory.

In recent years, organic photonic field-effect transistors have made remarkable progress with the rapid development of conjugated polycrystalline materials. Liquid crystals, with their smooth surface, defined layer thickness, and crystalline structures, are commonly used for these advantages. In this work, a series of smectic liquid crystalline molecules, 2,9-didecyl-dinaphtho-thienothiophene (C10-DNTT), 2,7-didecyl-benzothieno-benzothiopene (C10-BTBT), 3,9-didecyl-dinaphtho-thiophene (C10-DNT), and didecyl-sexithiophene (C10-6T), have been used in photonic transistor memory, functioning as both hole-transport channels and electron traps to investigate systematically the reasons and mechanisms behind the memory behavior of smectic liquid crystals. After thermal annealing, C10-BTBT and C10-6T/C10-DNTT are homeotropically aligned from the smectic A and smectic X phases, respectively. The 3D-ordered structure of these smectic-aligned crystals contributed to efficient photowriting and electrical erasing processes. Among them, the device performance of C10-BTBT was particularly significant, with a memory window of 21 V. The memory ratio could reach 1.5 × 106 and maintain a memory ratio of over 3 orders after 10,000 s, contributing to its smectic A structure. Through the research, we confirmed the memory and light/bias-gated behaviors of these smectic liquid crystalline molecules, attributing them to reversible molecular conformation transitions and the inherent structural inhomogeneity inside the polycrystalline channel layer.

Bicyclopentadithiophene-Based Organic Semiconductor for Stable and High-Performance Perovskite Solar Cells Exceeding 22.

Well-performing organic-inorganic halide perovskites are susceptible to poor efficiency and instability due to their various defects at the interphases, grain boundaries (GBs), and surfaces. In this study, an in situ method is utilized for effectively passivating the under-coordinated Pb2+ defects of perovskite with new non-fullerene acceptors (NFAs) (INXBCDT; X = H, Cl, and Br) through their carbonyl and cyano functional groups during the antisolvent dripping process. It reveals that the bicyclopentadithiophene (BCDT) core with highly electron-withdrawing end-capping groups passivates GBs and boosts perovskite grain growth. This effective defect passivation decreases the trap density to increase the carrier recombination lifetime of the perovskite film. As a result, bromo-substituted dicyanomethylene indanone (INBr)-end-capped BCDT (INBrBCDT-b8; 3a)-passivated devices exhibit the highest power conversion efficiency (PCE) of 22.20% (vs those of 18.09% obtained for perovskite films without passivation) upon an optimized film preparation process. Note that devices treated with more soluble 2-ethylhexyl-substituted compounds (1a, 2a, and 3a) exhibit higher PCE than those treated with less soluble octyl-substituted compounds (1b, 2b, and 3b). It is also worth noting that BCDT is a cost-effective six-ring core that is easier to synthesize with a higher yield and therefore much cheaper than those with highly fused-ring cores. In addition, a long-term stability test in a glovebox for 1500 h reveals that the perovskite solar cells (PSCs) based on a perovskite absorber treated with compound 3a maintain ∼90% of their initial PCE. This is the first example of the simplest high-conjugation additive for perovskite film to achieve a PCE greater than 22% of the corresponding lead-based PSCs.

High-Performance Phototransistor Memory with an Ultrahigh Memory Ratio Conferred Using Hydrogen-Bonded Supramolecular Electrets.

As the research of photonic electronics thrives, the enhanced efficacy from an optic unit cell can considerably improve the performance of an optoelectronic device. In this regard, organic phototransistor memory with a fast programming/readout and a distinguished memory ratio produces an advantageous outlook to fulfill the demand for advanced applications. In this study, a hydrogen-bonded supramolecular electret is introduced into the phototransistor memory, which comprises porphyrin dyes, meso-tetra(4-aminophenyl)porphine, meso-tetra(p-hydroxyphenyl)porphine, and meso-tetra(4-carboxyphenyl)porphine (TCPP), and insulated polymers, poly(4-vinylpyridine) and poly(4-vinylphenol) (PVPh). To combine the optical absorption of porphyrin dyes, dinaphtho[2,3-b:2',3'-f]thieno[3,2-b]thiophene (DNTT) is selected as a semiconducting channel. The porphyrin dyes serve as the ambipolar trapping moiety, while the insulated polymers form a barrier to stabilize the trapped charges by forming hydrogen-bonded supramolecules. We find that the hole-trapping capability of the device is determined by the electrostatic potential distribution in the supramolecules, whereas the electron-trapping capability and the surface proton doping originated from hydrogen bonding and interfacial interactions. Among them, PVPh:TCPP with an optimal hydrogen bonding pattern in the supramolecular electret produces the highest memory ratio of 1.12 × 108 over 104 s, which is the highest performance among the reported achievements. Our results suggest that the hydrogen-bonded supramolecular electret can enhance the memory performance by fine-tuning their bond strength and cast light on a potential pathway to future photonic electronics.

N-Type Doping of Naphthalenediimide-Based Random Donor-Acceptor Copolymers to Enhance Transistor Performance and Structural Crystallinity.

An integrated strategy of molecular design and conjugated polymer doping is proposed to improve the electronic characteristics for organic field effect transistor (OFET) applications. Here, a series of soluble naphthalene diimide (NDI)-based random donor-acceptor copolymers with selenophene π-conjugated linkers and four acceptors with different electron-withdrawing strengths (named as rNDI-N/S/NN/SS) are synthesized, characterized, and used for OFETs. N-type doping of NDI-based random copolymers using (12a,18a)-5,6,12,12a,13,18,18a,19-octahydro-5,6-dimethyl-13,18[1',2']-benzenobisbenzimidazo[1,2-b:2',1'-d]benzo[i][2.5]benzodiazocine potassium triflate adduct (DMBI-BDZC) is successfully demonstrated. The undoped rNDI-N, rNDI-NN, and rNDI-SS samples exhibit ambipolar charge transport, while rNDI-S presents only a unipolar n-type characteristic. Doping with DMBI-BDZC significantly modulates the performance of rNDI-N/S OFETs, with a 3- to 6-fold increase in electron mobility (µe) for 1 wt % doped device due to simultaneous trap mitigation, lower contact resistance (RC), and activation energy (EA), and enhanced crystallinity and edge-on orientation for charge transport. However, the doping of intrinsic pro-quinoidal rNDI-NN/SS films exhibits unchanged or even reduced device performance. These findings allow us to manipulate the energy levels by developing conjugated copolymers based on various acceptors and quinoids and to optimize the dopant-polymer semiconductor interactions and their impacts on the film morphology and molecular orientation for enhanced charge transport.

Tunable Thermoelectric Performance of the Nanocomposites Formed by Diketopyrrolopyrrole/Isoindigo-Based Donor-Acceptor Random Conjugated Copolymers and Carbon Nanotubes.

This paper presents the development of thermoelectric properties in nanocomposites comprising donor-acceptor random conjugated copolymers and single-walled carbon nanotubes (SWCNTs). The composition of the conjugated polymers, specifically the ratio of diketopyrrolopyrrole (DPP) to isoindigo (IID), is manipulated to design a series of random conjugated copolymers (DPP0, DPP5, DPP10, DPP30, DPP50, DPP90, DPP95, and DPP100). The objective is to improve the dispersion of SWCNTs into smaller bundles, leading to enhanced thermoelectric properties of the polymer/SWCNT nanocomposite. This dispersion strategy promotes an interconnected conducting network, which plays a critical role in optimizing the thermoelectric performance. Accordingly, the effects of morphologies on the thermoelectric properties of the nanocomposites are systematically investigated. The DPP95/SWCNT nanocomposite exhibits the strongest interaction, resulting in the highest power factor (PF) of 711.1 µW m-1 K-2, derived from the high electrical conductivity of 1690 S cm-1 and Seebeck coefficient of 64.8 µV K-1. The prototype flexible thermoelectric generators assembled with a DPP95/SWCNT film achieve a maximum power output of 20.4 µW m-2 at a temperature difference of 29.3 K. These findings highlight the potential of manipulating the composition of random conjugated copolymers and incorporating SWCNTs to efficiently harvest low-grade waste heat in wearable thermoelectric devices.

Mixed Ionic-Electronic Conducting Hydrogels with Carboxylated Carbon Nanotubes for High Performance Wearable Thermoelectric Harvesters.

Mixed ionic-electronic conducting (MIEC) thermoelectric (TE) materials offer higher ionic conductivity and ionic Seebeck coefficient compared to those of purely ionic-conducting TE materials. These characteristics make them suitable for direct use in thermoelectric generators (TEGs) as the charge carriers can be effectively transported from one electrode to the other via the external circuit. In the present study, MIEC hydrogels are fabricated via the chemical cross-linking of polyacrylamide (PAAM) and polydopamine (PDA) to form a double network. In addition, electrically conducting carboxylated carbon nanotubes (CNT-COOH) are dispersed evenly within the hydrogel via sonication and interaction with the PDA. Moreover, the electrical properties of the hydrogel are further improved via the in situ polymerization of polyaniline (PANI). The presence of CNT-COOH facilitates the ionic conductivity and enhances the ionic Seebeck coefficient via ionic-electronic interactions between sodium ions and carboxyl groups on CNT-COOH, which can be observed in X-ray photoelectron spectroscopy results, thereby promoting the charge transport properties. As a result, the optimum device exhibits a remarkable ionic conductivity of 175.3 mS cm-1 and a high ionic Seebeck coefficient of 18.6 mV K-1, giving an ionic power factor (PFi) of 6.06 mW m-1 K-2 with a correspondingly impressive ionic figure of merit (ZTi) of 2.65. These values represent significant achievements within the field of gel-state organic TE materials. Finally, a wearable module is fabricated by embedding the PAAM/PDA/CNT-COOH/PANI hydrogel into a poly(dimethylsiloxane) mold. This configuration yields a high power density of 171.4 mW m-2, thus highlighting the considerable potential for manufacturing TEGs for wearable devices capable of harnessing waste heat.