Boosting the Thermoelectric Performance of the Doped DPP-EDOT Conjugated Polymer by Incorporating an Ionic Additive.

The thermoelectric (TE) performance of organic materials is limited by the coupling of Seebeck coefficient and electrical conductivity. Herein a new strategy is reported to boost the Seebeck coefficient of conjugated polymer without significantly reducing the electrical conductivity by incorporation of an ionic additive DPPNMe3 Br. The doped polymer PDPP-EDOT thin film exhibits high electrical conductivity up to 1377 ± 109 S cm-1 but low Seebeck coefficient below 30 µV K-1 and a maximum power factor of 59 ± 10 µW m-1 K-2 . Interestingly, incorporation of small amount (at a molar ratio of 1:30) of DPPNMe3 Br into PDPP-EDOT results in the significant enhancement of Seebeck coefficient along with the slight decrease of electrical conductivity after doping. Consequently, the power factor (PF) is boosted to 571 ± 38 µW m-1 K-2 and ZT reaches 0.28 ± 0.02 at 130 °C, which is among the highest for the reported organic TE materials. Based on the theoretical calculation, it is assumed that the enhancement of TE performance for the doped PDPP-EDOT by DPPNMe3 Br is mainly attributed to the increase of energetic disorder for PDPP-EDOT.

Chemical doping of organic semiconductors for thermoelectric applications.

Doping is essential to manipulate the electrical performance of both thermoelectric (TE) materials and organic semiconductors (OSCs). Although organic thermoelectric (OTE) materials have experienced a rapid development over the past decade, the chemical doping of OSCs for TE applications lags behind, which has limited further breakthroughs in this cutting-edge field. Recently, increasing efforts have been devoted to the development of energetically matched host and dopant molecules, exploring novel doping methods and revealing the doping mechanisms. This tutorial review covers the basic mechanisms, fundamental requirements, recent advances and remaining challenges of chemical doping in OSCs for TE applications. We first present the basic knowledge of the trade-off relationship in TE materials and its critical requirements for doped OSCs, followed by a brief introduction of recent advances in the molecular design of OSCs and dopants. Moreover, we provide an overview of the existing categories of doping mechanisms and methods, and more importantly, emphasize the summarized doping strategies for the state-of-the-art OTE materials. Finally, challenges and perspectives on the chemical doping of OSCs are proposed to highlight the research directions that deserve attention towards a bright future of OTE materials.

Enabling Multifunctional Organic Transistors with Fine-Tuned Charge Transport.

Organic field-effect transistors (OFETs) are promising candidates for many electronic applications not only because of the intrinsic features of organic semiconductors in mechanical flexibility and solution processability but also owing to their multifunctionalities promised by combined signal switching and transduction properties. In contrast to rapid developments of high performance devices, the construction of multifunctional OFETs remains challenging. A key issue is fine-tuning the charge transport by modulating electric fields that are coupled with various external stimuli. Given that the charge transport is determined by complicated factors involving material and device engineering, the development of effective strategies to manipulate charge transport is highly desired toward state-of-the-art multifunctional OFETs. In this Account, we present our recent progress on device-engineered OFETs for sensing applications and thermoelectric studies of organic semiconductors. The interactions between organic semiconductors and the target analyte determine the performance of chemical sensors based on OFETs. We introduced gas receptors and in situ tailored molecular antenna on the surface of ultrathin active layers. The engineered interfaces enable direct and specific semiconductor-analyte interactions, as demonstrated in developed chemical sensors and biosensors with prominent sensitivity and good selectivity. In comparison with chemical stimuli, many physical stimuli such as pressure typically possess a limit effect on the charge transport properties of organic semiconductors. By utilizing the suspended-gate geometry, the carrier concentration in a conductive channel can be controlled quantitatively by the pressure dominated changes in the capacitance of an air dielectric layer, allowing for ultrasensitive pressure detection in a unique manner. More importantly, the transduced current can be further processed by a synaptic OFET, in which the proton/electron coupling interfaces contribute to the dynamic modulation of carrier concentration, thus mimicking biological synapses. The integrated pressure sensor and synaptic OFETs, namely, the dual-organic-transistor-based tactile-perception element, has exhibited promising applications in artificial intelligence elements. Aiming at revealing thermoelectric (TE) properties of organic semiconductors, we also investigated field-modulated TE performance of several high-mobility semiconductors by varying the driving electric field to the temperature gradient. This has been confirmed to offer a strategy to accelerate the search for promising TE materials from well-developed organic semiconductors. By tuning the charge transport process in the device, the functional modulation of OFETs has experienced significant progress in the preceding years. The exploration of new ways to create OFETs with more fascinating functionalities is still full of opportunities to obtain greater benefit from organic transistors.

A Conjugated Polymer Containing Arylazopyrazole Units in the Side Chains for Field-Effect Transistors Optically Tunable by Near Infra-Red Light.

Optically tunable field-effect transistors (FETs) with near infra-red (NIR) light show promising applications in various areas. Now, arylazopyrazole groups are incorporated in the side chains of a semiconducting donor-acceptor (D-A) polymer. The cis-trans interconversion of the arylazopyrazole can be controlled by 980 nm and 808 nm NIR light irradiation, by utilizing NaYF4 :Yb,Tm upconversion nanoparticles and the photothermal effect of conjugated D-A polymers, respectively. This reversible transformation affects the interchain packing of the polymer thin film, which in turn reversibly tunes the semiconducting properties of the FETs by the successive 980 nm and 808 nm light irradiation. The resultant FETs display fast response to NIR light, good resistance to photofatigue, and stability in storage for up to 120 days. These unique features will be useful in future memory and bioelectronic wearable devices.

2D Semiconducting Metal-Organic Framework Thin Films for Organic Spin Valves.

2D conductive metal-organic frameworks (2D c-MOFs) feature promising applications as chemiresistive sensors, electrode materials, electrocatalysts, and electronic devices. However, exploration of the spin-polarized transport in this emerging materials and development of the relevant spintronics have not yet been implemented. In this work, layer-by-layer assembly was applied to fabricate highly crystalline and oriented thin films of a 2D c-MOF, Cu3 (HHTP)2 , (HHTP: 2,3,6,7,10,11-hexahydroxytriphenylene), with tunable thicknesses on the La0.67 Sr0.33 MnO3 (LSMO) ferromagnetic electrode. The magnetoresistance (MR) of the LSMO/Cu3 (HHTP)2 /Co organic spin valves (OSVs) reaches up to 25 % at 10 K. The MR can be retained with good film thickness adaptability varied from 30 to 100 nm and also at high temperatures (up to 200 K). This work demonstrates the first potential applications of 2D c-MOFs in spintronics.

Selenium-Substituted Diketopyrrolopyrrole Polymer for High-Performance p-Type Organic Thermoelectric Materials.

Development of high-performance organic thermoelectric (TE) materials is of vital importance for flexible power generation and solid-cooling applications. Demonstrated here is the significant enhancement in TE performance of selenium-substituted diketopyrrolopyrrole (DPP) derivatives. Along with strong intermolecular interactions and high Hall mobilities of 1.0-2.3 cm2 V-1 s-1 in doping-states for polymers, PDPPSe-12 exhibits a maximum power factor and ZT of up to 364 µW m-1 K-2 and 0.25, respectively. The performance is more than twice that of the sulfur-based DPP derivative and represents the highest value for p-type organic thermoelectric materials based on high-mobility polymers. These results reveal that selenium substitution can serve as a powerful strategy towards rationally designed thermoelectric polymers with state-of-the-art performances.

Conjugated-Backbone Effect of Organic Small Molecules for n-Type Thermoelectric Materials with ZT over 0.2.

Conjugated backbones play a fundamental role in determining the electronic properties of organic semiconductors. On the basis of two solution-processable dihydropyrrolo[3,4-c]pyrrole-1,4-diylidenebis(thieno[3,2-b]thiophene) derivatives with aromatic and quinoid structures, we have carried out a systematic study of the relationship between the conjugated-backbone structure and the thermoelectric properties. In particular, a combination of UV-vis-NIR spectra, photoemission spectroscopy, and doping optimization are utilized to probe the interplay between energy levels, chemical doping, and thermoelectric performance. We found that a moderate change in the conjugated backbone leads to varied doping mechanisms and contributes to dramatic changes in the thermoelectric performance. Notably, the chemically doped A-DCV-DPPTT, a small molecule with aromatic structure, exhibits an electrical conductivity of 5.3 S cm-1 and a high power factor (PF373 K) up to 236 µW m-1 K-2, which is 50 times higher than that of Q-DCM-DPPTT with a quinoid structure. More importantly, the low thermal conductivity enables A-DCV-DPPTT to possess a figure of merit (ZT) of 0.23 ± 0.03, which is the highest value reported to date for thermoelectric materials based on organic small molecules. These results demonstrate that the modulation of the conjugated backbone represents a powerful strategy for tuning the electronic structure and mobility of organic semiconductors toward a maximum thermoelectric performance.

Trichalcogenasumanene ortho-Quinones: Synthesis, Properties, and Transformation into Various Heteropolycycles.

The regioselective transformation of heterobuckybowl trichalcogenasumanenes 1 a,b at peripheral butoxy groups afforded trichalcogenasumanene ortho-quinones 2 a,b. Compounds 2 a,b are distinct from 1 a,b in terms of their molecular geometry and electronic state; that is, they have a shallower bowl depth and show absorbance in the NIR region. The reaction of 2 a,b with diamines resulted in a variety of heteropolycycles, including molecular spoon 3 a-6 a, planar π-systems 3 b-6 b, and highly twisted [7-6-6]-fused systems 7 a,b. These new heteropolycycles had different optical/electrical properties: 4 a,b showed hole mobility of approximately 0.002 cm2 V-1 s-1 , 6 a displayed red emission in both solution and the solid state, and 7 a,b formed tight stacks of the curved π-surface.

Dithienoindophenines: p-Type Semiconductors Designed by Quinoid Stabilization for Solar-Cell Applications.

Compared with the dominant aromatic conjugated materials, photovoltaic applications of their quinoidal counterparts featuring rigid and planar molecular structures have long been unexplored despite their narrow optical bandgaps, large absorption coefficients, and excellent charge-transport properties. The design and synthesis of dithienoindophenine derivatives (DTIPs) by stabilizing the quinoidal resonance of the parent indophenine framework is reported here. Compared with the ambipolar indophenine derivatives, DTIPs with the fixed molecular configuration are found to be p-type semiconductors exhibiting excellent unipolar hole mobilities up to 0.22 cm2 V-1 s-1 , which is one order of magnitude higher than that of the parent IP-O and is even comparable to that of QQT(CN)4-based single-crystal field-effect transistors (FET). DTIPs exhibit better photovoltaic performance than their aromatic bithieno[3,4-b]thiophene (BTT) counterparts with an optimal power-conversion efficiency (PCE) of 4.07 %.

Bismuth Interfacial Doping of Organic Small Molecules for High Performance n-type Thermoelectric Materials.

Development of chemically doped high performance n-type organic thermoelectric (TE) materials is of vital importance for flexible power generating applications. For the first time, bismuth (Bi) n-type chemical doping of organic semiconductors is described, enabling high performance TE materials. The Bi interfacial doping of thiophene-diketopyrrolopyrrole-based quinoidal (TDPPQ) molecules endows the film with a balanced electrical conductivity of 3.3 S cm(-1) and a Seebeck coefficient of 585 µV K(-1) . The newly developed TE material possesses a maximum power factor of 113 µW m(-1) K(-2) , which is at the forefront for organic small molecule-based n-type TE materials. These studies reveal that fine-tuning of the heavy metal doping of organic semiconductors opens up a new strategy for exploring high performance organic TE materials.

Toward High Performance n-Type Thermoelectric Materials by Rational Modification of BDPPV Backbones.

Three n-type polymers BDPPV, ClBDPPV, and FBDPPV which exhibit outstanding electrical conductivities when mixed with an n-type dopant, N-DMBI ((4-(1,3-dimethyl-2,3-dihydro-1H-benzoimidazol-2-yl)phenyl)dimethylamine), in solution. High electron mobility and an efficient doping process endow FBDPPV with the highest electrical conductivities of 14 S cm(-1) and power factors up to 28 µW m(-1) K(-2), which is the highest thermoelectric (TE) power factor that has been reported for solution processable n-type conjugated polymers. Our investigations reveal that introduction of halogen atoms to the polymer backbones has a dramatic influence on not only the electron mobilities but also the doping levels, both of which are critical to the electrical conductivities. This work suggests the significance of rational modification of polymer structures and opens the gate for applying the rapidly developed organic semiconductors with high carrier mobilities to thermoelectric field.

Two-dimensional π-expanded quinoidal terthiophenes terminated with dicyanomethylenes as n-type semiconductors for high-performance organic thin-film transistors.

Quinoidal oligothiophenes (QOT), as classical n-type semiconductors, have been well-known for a long time but with non-optimal semiconducting properties. We report here the design and selective synthesis of new two-dimensional (2D) π-expanded quinoidal terthiophenes, 2DQTTs, with proximal (2DQTT-i) and distal (2DQTT-o) regiochemistry for high-performance n-channel organic thin-film transistors (n-OTFTs) featuring high electron mobility, solution processability, and ambient stability. The elegant combination of thieno[3,4-b]thiophene [TT, donor (D)] and 5-alkyl-4H-thieno[3,4-c]pyrrole-4,6(5H)-dione [TPD, acceptor (A)] units with relatively large π-surface endows these 2DQTTs with distinctive 2D structural characteristics and flat configuration stabilized by weak intramolecular S-O/S weak interactions. Furthermore, the A-D-A-D-A electronic structure maintains an adequately low LUMO energy level. These 2DQTTs are shown to exhibit outstanding semiconducting properties with electron mobilities of up to 3.0 cm(2) V(-1) s(-1) and on/off ratios of up to 10(6) (2DQTT-o) in ambient- and solution-processed OTFTs. Investigations on thin-film morphology reveal that the microstructure of 2DQTTs is highly dependent on the orientation of the fused thiophene subunits, leading to differences in electron mobilities of 1 order of magnitude. X-ray diffraction studies in particular reveal increased crystallinity, crystalline coherence, and orientational order in 2DQTT-o compared to 2DQTT-i, which accounts for the superior electron transport property of 2DQTT-o.

Thieno[3,2-b]thiophene-diketopyrrolopyrrole-based quinoidal small molecules: synthesis, characterization, redox behavior, and n-channel organic field-effect transistors.

We report the synthesis, characterization, redox behavior, and n-channel organic field-effect (OFET) characteristics of a new class of thieno[3,2-b]thiophene-diketopyrrolopyrrole-based quinoidal small molecules 3 and 4. Under ambient atmosphere, solution-processed thin-film transistors based on 3 and 4 exhibit maximum electron mobilities up to 0.22 and 0.16 cm(2) V(-1) s(-1) , respectively, with on-off current ratios (Ion /Ioff ) of more than than 10(6) . Cyclic voltammetry analysis showed that this class of quinoidal derivatives exhibited excellent reversible two-stage reduction behavior. This property was further investigated by a stepwise reductive titration of 4, in which sequential reduction to the radical anion and then the dianion were observed.

High-Performance and Ecofriendly Organic Thermoelectrics Enabled by N-Type Polythiophene Derivatives with Doping-Induced Molecular Order.

The ability of n-type polymer thermoelectric materials to tolerate high doping loading limits further development of n-type polymer conductivity. Herein, two alcohol-soluble n-type polythiophene derivatives that are n-PT3 and n-PT4 are reported. Due to the ability of two polymers to tolerate doping loading more significantly than 100 mol%, both achieve electrical conductivity >100 S cm-1 . Moreover, the conductivity of both polythiophenes remains almost constant at high doping concentrations with excellent doping tunability, which may be related to their ability to overcome charging-induced backbone torsion and morphology change caused by saturated doping. The characterizations reveal that n-PT4 has a high doping level and carrier concentration (>3.10 × 1020  cm-3 ), and the carrier concentration continues to increase as the doping concentration increases. In addition, doping leads to improved crystal structure of n-PT4, and the crystallinity does not decrease significantly with increasing doping concentration; even the carrier mobility increases with it. The synergistic effect of these two leads to both n-PT3 and n-PT4 achieving a breakthrough of 100 in conductivity and power factor. The DMlmC-doped n-PT4 achieves a power factor of over 150 µW m-1  K-2 . These values are among the highest for n-type organic thermoelectric materials.

Evolution of Musculoskeletal Electronics.

The musculoskeletal system, constituting the largest human physiological system, plays a critical role in providing structural support to the body, facilitating intricate movements, and safeguarding internal organs. By virtue of advancements in revolutionized materials and devices, particularly in the realms of motion capture, health monitoring, and postoperative rehabilitation, "musculoskeletal electronics" has actually emerged as an infancy area, but has not yet been explicitly proposed. In this review, the concept of musculoskeletal electronics is elucidated, and the evolution history, representative progress, and key strategies of the involved materials and state-of-the-art devices are summarized. Therefore, the fundamentals of musculoskeletal electronics and key functionality categories are introduced. Subsequently, recent advances in musculoskeletal electronics are presented from the perspectives of "in vitro" to "in vivo" signal detection, interactive modulation, and therapeutic interventions for healing and recovery. Additionally, nine strategy avenues for the development of advanced musculoskeletal electronic materials and devices are proposed. Finally, concise summaries and perspectives are proposed to highlight the directions that deserve focused attention in this booming field.

Nanoscale doping of polymeric semiconductors with confined electrochemical ion implantation.

Nanoresolved doping of polymeric semiconductors can overcome scaling limitations to create highly integrated flexible electronics, but remains a fundamental challenge due to isotropic diffusion of the dopants. Here we report a general methodology for achieving nanoscale ion-implantation-like electrochemical doping of polymeric semiconductors. This approach involves confining counterion electromigration within a glassy electrolyte composed of room-temperature ionic liquids and high-glass-transition-temperature insulating polymers. By precisely adjusting the electrolyte glass transition temperature (Tg) and the operating temperature (T), we create a highly localized electric field distribution and achieve anisotropic ion migration that is nearly vertical to the nanotip electrodes. The confined doping produces an excellent resolution of 56 nm with a lateral-extended doping length down to as little as 9.3 nm. We reveal a universal exponential dependence of the doping resolution on the temperature difference (Tg - T) that can be used to depict the doping resolution for almost infinite polymeric semiconductors. Moreover, we demonstrate its implications in a range of polymer electronic devices, including a 200% performance-enhanced organic transistor and a lateral p-n diode with seamless junction widths of <100 nm. Combined with a further demonstration in the scalability of the nanoscale doping, this concept may open up new opportunities for polymer-based nanoelectronics.

Fullerene/sulfur-bridged annulene cocrystals: two-dimensional segregated heterojunctions with ambipolar transport properties and photoresponsivity.

Fullerene/sulfur-bridged annulene cocrystals with a two-dimensional segregated alternating layer structure were prepared by a simple solution process. Single-crystal analysis revealed the existence of continuing π-π interactions in both the donor and acceptor layers, which serve as transport paths for holes and electrons separately. The ambipolar transport behaviors were demonstrated with single-crystal field-effect transistors and rationalized by quantum calculations. Meanwhile, preliminary photoresponsivity was observed with the transistor configuration.

Critical role of alkyl chain branching of organic semiconductors in enabling solution-processed N-channel organic thin-film transistors with mobility of up to 3.50 cm² V(-1) s(-1).

Substituted side chains are fundamental units in solution processable organic semiconductors in order to achieve a balance of close intermolecular stacking, high crystallinity, and good compatibility with different wet techniques. Based on four air-stable solution-processed naphthalene diimides fused with 2-(1,3-dithiol-2-ylidene)malononitrile groups (NDI-DTYM2) that bear branched alkyl chains with varied side-chain length and different branching position, we have carried out systematic studies on the relationship between film microstructure and charge transport in their organic thin-film transistors (OTFTs). In particular synchrotron measurements (grazing incidence X-ray diffraction and near-edge X-ray absorption fine structure) are combined with device optimization studies to probe the interplay between molecular structure, molecular packing, and OTFT mobility. It is found that the side-chain length has a moderate influence on thin-film microstructure but leads to only limited changes in OTFT performance. In contrast, the position of branching point results in subtle, yet critical changes in molecular packing and leads to dramatic differences in electron mobility ranging from ~0.001 to >3.0 cm(2) V(-1) s(-1). Incorporating a NDI-DTYM2 core with three-branched N-alkyl substituents of C(11,6) results in a dense in-plane molecular packing with an unit cell area of 127 Å(2), larger domain sizes of up to 1000 × 3000 nm(2), and an electron mobility of up to 3.50 cm(2) V(-1) s(-1), which is an unprecedented value for ambient stable n-channel solution-processed OTFTs reported to date. These results demonstrate that variation of the alkyl chain branching point is a powerful strategy for tuning of molecular packing to enable high charge transport mobilities.

Extended π-conjugated molecules derived from naphthalene diimides toward organic emissive and semiconducting materials.

In this paper, a new synthetic way to modify naphthalene diimide (NDI) at "shoulder" positions is reported. The key step of the transformation is the intramolecular cyclization involving ethynyl and imidecarbonyl groups. The structure of the intermediate pyrylium cation was confirmed by X-ray crystal structural analysis. New conjugated molecules 1a-g were successfully synthesized in acceptable yields. Their absorption and fluorescence spectra were measured. Among them 1c-f are strongly emissive in solutions. Furthermore, 1b-f are also fluorescent in their solid states; in particular, 1b exhibits a typical aggregation-induced enhanced emission feature. Yellow-emissive microfibrils of 1d show potential optical waveguide behavior. HOMO/LUMO energies of 1a-f were determined based on their cyclic voltammograms. The results also reveal that HOMO/LUMO energies of these new conjugated molecules are influenced by the two flanking moieties. Notably, the thin film of 1c that is emissive shows p-type semiconducting behavior with hole mobility up to 0.0063 cm(2) V(-1) s(-1) based on the transfer and output characteristics of the OFET (organic field effect transistor).

Solid state ionics enabled ultra-sensitive detection of thermal trace with 0.001K resolution in deep sea.

The deep sea remains the largest uncharted territory on Earth because it's eternally dark under high pressure and the saltwater is corrosive and conductive. The harsh environment poses great difficulties for the durability of the sensing method and the device. Sea creatures like sharks adopt an elegant way to detect objects by the tiny temperature differences in the seawater medium using their extremely thermo-sensitive thermoelectric sensory organ on the nose. Inspired by shark noses, we designed and developed an elastic, self-healable and extremely sensitive thermal sensor which can identify a temperature difference as low as 0.01 K with a resolution of 0.001 K. The sensor can work reliably in seawater or under a pressure of 110 MPa without any encapsulation. Using the integrated temperature sensor arrays, we have constructed a model of an effective deep water mapping and detection device.