Flexible cooling devices, which aim to fulfill the essential requirement of complex working environments and enable local heat dissipation, have become the cutting‐edge area of refrigeration ...technology. Thermoelectric (TE) material represents a promising candidate for various flexible cooling applications, including wearable personal thermoregulation devices. With the increasing interest in the Peltier effect of conductive polymers and inorganic films on flexible substrates, flexible cooling devices have undergone rapid development. Herein, the fundamental mechanisms, basic parameters, and temperature measurement techniques for evaluating the cooling performance are summarized. Moreover, recent progress on TE materials, such as flexible inorganic and organic materials for Peltier cooling studies, is reviewed. More importantly, insights are provided into the key strategies for high‐performance Peltier devices. The final part details the existing challenges and perspectives on flexible TE cooling to inspire additional research interests toward the advancement of refrigeration technology.
Peltier devices are promising candidates for flexible cooling applications. In this review, the fundamental mechanisms, measurement techniques, recent progress, and key strategies toward state‐of‐the‐art cooling applications are summarized.
Multi‐functional organic field‐effect transistors (OFETs), an emerging focus of organic optoelectronic devices, hold great potential for a variety of applications. This report introduces recent ...progress on multi‐functional OFETs including OFETs based sensors, phototransistors, light‐emitting transistors, memory cells, and magnetic field‐effect OFETs. Key strategies towards multi‐ functional integration of OFETs, which involves the exploration of functional materials, interfaces modifications, modulation of condensed structures, optimization of device geometry, and device integration, are summarized. Furthermore, remaining challenges and perspectives are discussed, giving a comprehensive overview of multi‐functional OFETs.
Organic thin‐film transistors (OFETs) represent a promising candidate for next‐generation sensing applications because of the intrinsic advantages of organic semiconductors. The development of ...flexible sensing devices has received particular interest in the past few years. The recent efforts of developing OFETs for sensitive and specific flexible sensors are summarized from the standpoint of device engineering. The tuning of signal transduction and signal amplification are highlighted based on an overview of active‐layer thickness modulation, functional receptor implantation and device geometry optimization.
Recent efforts in developing highly sensitive and specific flexible sensors in terms of active‐layer thickness modulation, functional receptor implantation, and device geometry optimization are briefly summarized with an outlook on future requirements.
Organic‐device‐based tactile‐perception systems can open up new opportunities for the next generation of intelligent products. To meet the critical requirements of artificial perception systems, the ...efficient construction of organic smart elements with integrated sensing and signal processing functionalities is highly desired, but remains a challenge. This study presents a dual‐organic‐transistor‐based tactile‐perception element (DOT‐TPE) with biomimetic functionality by the construction of organic synaptic transistors with integrated sensing transistors. The unique geometry of the DOT‐TPE permits instantaneous sensing of pressure stimuli and synapse‐like processing of an electric signal in a single element. More importantly, these organic‐transistor‐based tactile‐perception elements can be built into arrays to serve as bionic tactile‐perception systems. The combined biomimetic functionality of tactile‐perception systems, together with their promising features of flexibility and large‐area fabrication, makes this work represent a step forward toward novel e‐skin devices for artificial intelligence.
By the construction of organic synaptic transistors with integrated sensing transistors, a dual‐organic‐transistor‐based tactile‐perception element with pressure sensing and synapse‐like signal‐processing functions in a single element is demonstrated. This biomimetic functionality makes this work represent a step forward toward novel e‐skin devices for artificial intelligence.
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 La0.67Sr0.33MnO3 (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.
2D c‐MOF based organic spin valves: Layer‐by‐layer assembly was applied to fabricate highly crystalline and oriented thin films of 2D conductive MOF, Cu3(HHTP)2, on the La0.67Sr0.33MnO3 (LSMO) ferromagnetic electrode. A large magnetoresistance of 25 % for this LSMO/Cu3(HHTP)2/Co organic spin valve was achieved. This work demonstrates promising applications of 2D c‐MOFs in spintronics.
Organic thermoelectric (OTE) materials have attracted intensive attention because of their promising applications in flexible electricity generators and ultrathin solid cooling elements. The ...well-developed high mobility organic semiconductors (OSCs) are considered to be excellent candidates for high performance OTE materials. Although a variety of OSCs have been explored as OTE materials, their intrinsic potential has not been revealed owing to limited understanding of the structure–property relationship, an unsatisfied doping method, etc. In this perspective, we briefly review the requirements of OTE conversion and discuss the major strategies to develop high performance OTE materials from OSC candidates. We then introduce some achievements made with p- and n-type OSCs to provide a clear map of the development status. Finally, we detail our viewpoint of the opportunities and challenges in this cutting-edge field. We highlight that OSC-based TE study is an emerging topic in organic electronics and that there is a long way to go to get the true benefits of OTE materials.
Skin-like temperature- and pressure-sensing capabilities are essential features for the next generation of artificial intelligent products. Previous studies of e-skin and smart elements have focused ...on flexible pressure sensors, whereas the simultaneous and sensitive detection of temperature and pressure with a single device remains a challenge. Here we report developing flexible dual-parameter temperature-pressure sensors based on microstructure-frame-supported organic thermoelectric (MFSOTE) materials. The effective transduction of temperature and pressure stimuli into two independent electrical signals permits the instantaneous sensing of temperature and pressure with an accurate temperature resolution of <0.1 K and a high-pressure-sensing sensitivity of up to 28.9 kPa(-1). More importantly, these dual-parameter sensors can be self-powered with outstanding sensing performance. The excellent sensing properties of MFSOTE-based devices, together with their unique advantages of low cost and large-area fabrication, make MFSOTE materials possess promising applications in e-skin and health-monitoring elements.
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 DPPNMe3Br. 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 DPPNMe3Br 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 DPPNMe3Br is mainly attributed to the increase of energetic disorder for PDPP‐EDOT.
Packed in: The doped DPP (diketopyrrolopyrole)‐EDOT(3,4‐ethlenedioxythiophene) polymer shows high thermoelectric performance with PF = 571 ± 38 µW m−1 K−2 and ZT = 0.28 ± 0.02, after incorporation of an ionic additive, which can boost the Seebeck coefficient through increasing the energetic disorder and decreasing the p‐type doping degree.
Solution‐processable highly conductive polymers are of great interest in emerging electronic applications. For p‐doped polymers, conductivities as high a nearly 105 S cm−1 have been reported. In the ...case of n‐doped polymers, they often fall well short of the high values noted above, which might be achievable, if much higher charge‐carrier mobilities determined could be realized in combination with high charge‐carrier densities. This is in part due to inefficient doping and dopant ions disturbing the ordering of polymers, limiting efficient charge transport and ultimately the achievable conductivities. Here, n‐doped polymers that achieve a high conductivity of more than 90 S cm−1 by a simple solution‐based co‐deposition method are reported. Two conjugated polymers with rigid planar backbones, but with disordered crystalline structures, exhibit surprising structural tolerance to, and excellent miscibility with, commonly used n‐dopants. These properties allow both high concentrations and high mobility of the charge carriers to be realized simultaneously in n‐doped polymers, resulting in excellent electrical conductivity and thermoelectric performance.
Two conjugated polymers with rigid planar backbones, but with disordered crystalline structures, exhibit surprising structural tolerance to commonly used n‐dopants. These properties allow both high concentrations and high mobility of the charge carriers to be realized simultaneously in n‐doped polymers, resulting in excellent electrical conductivity of over 90 S cm−1 and thermoelectric performance up to 106 µW m−1 K−2.
Thermoelectric materials have attracted more attention in recent years, which can be corroborated by the increasing scientific publications. Moreover, the optimistic prediction for the thermoelectric ...industry proves that the practicability of thermoelectric technology is further acknowledged. Recently, benefitting from the rapid development of organic electronics, the research of organic thermoelectric (OTE) materials is receiving particular interest. Cooperation and complementation between organic and inorganic thermoelectric materials could promote the broader application of thermoelectric effect. To realize high conversion efficiency of thermoelectric device, high‐performance p‐ and n‐type OTE materials are both necessary. However, the instability of most n‐type organic materials in air impedes their application for high‐performance thermoelectric conversion. Therefore, more efforts should be made to promote relevant research and applications. Herein, the research progress on OTE materials (n‐type) and devices is reviewed to show readers some details of n‐type OTE research and give some guidelines for further explorations.
Lightweight and flexible organic thermoelectric materials are attracting more attention, driven by the growing demands for maintenance of free power for wearable electronics and internet of things. Remarkable developments have been achieved in the past years for n‐type organic thermoelectric materials. The research progress is reviewed to show the state‐of‐art achievements and give a brief view of this field.
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