Temperature is one of the most important environmental stimuli to record and amplify. While traditional thermoelectric materials are attractive for temperature/heat flow sensing applications, their ...sensitivity is limited by their low Seebeck coefficient (∼100 μV K
). Here we take advantage of the large ionic thermoelectric Seebeck coefficient found in polymer electrolytes (∼10,000 μV K
) to introduce the concept of ionic thermoelectric gating a low-voltage organic transistor. The temperature sensing amplification of such ionic thermoelectric-gated devices is thousands of times superior to that of a single thermoelectric leg in traditional thermopiles. This suggests that ionic thermoelectric sensors offer a way to go beyond the limitations of traditional thermopiles and pyroelectric detectors. These findings pave the way for new infrared-gated electronic circuits with potential applications in photonics, thermography and electronic-skins.
Heat is an abundant but often wasted source of energy. Thus, harvesting just a portion of this tremendous amount of energy holds significant promise for a more sustainable society. While traditional ...solid-state inorganic semiconductors have dominated the research stage on thermal-to-electrical energy conversion, carbon-based semiconductors have recently attracted a great deal of attention as potential thermoelectric materials for low-temperature energy harvesting, primarily driven by the high abundance of their atomic elements, ease of processing/manufacturing, and intrinsically low thermal conductivity. This quest for new materials has resulted in the discovery of several new kinds of thermoelectric materials and concepts capable of converting a heat flux into an electrical current by means of various types of particles transporting the electric charge: (i) electrons, (ii) ions, and (iii) redox molecules. This has contributed to expanding the applications envisaged for thermoelectric materials far beyond simple conversion of heat into electricity. This is the motivation behind this review. This work is divided in three sections. In the first section, we present the basic principle of the thermoelectric effects when the particles transporting the electric charge are
,
, and
and describe the conceptual differences between the three thermodiffusion phenomena. In the second section, we review the efforts made on developing devices exploiting these three effects and give a thorough understanding of what limits their performance. In the third section, we review the state-of-the-art thermoelectric materials investigated so far and provide a comprehensive understanding of what limits charge and energy transport in each of these classes of materials.
Efficiency, current throughput, and speed of electronic devices are to a great extent dictated by charge carrier mobility. The classic approach to impart high carrier mobility to polymeric ...semiconductors has often relied on the assumption that extensive order and crystallinity are needed. Recently, however, this assumption has been challenged, because high mobility has been reported for semiconducting polymers that exhibit a surprisingly low degree of order. Here, we show that semiconducting polymers can be confined into weakly ordered fibers within an inert polymer matrix without affecting their charge transport properties. In these conditions, the semiconducting polymer chains are inhibited from attaining long-range order in the π-stacking or alkyl-stacking directions, as demonstrated from the absence of significant X-ray diffraction intensity corresponding to these crystallographic directions, yet still remain extended along the backbone direction and aggregate on a local length scale. As a result, the polymer films maintain high mobility even at very low concentrations. Our findings provide a simple picture that clarifies the role of local order and connectivity of domains.
The evolution of the society is characterized by an increasing flow of information from things to the internet. Sensors have become the cornerstone of the internet‐of‐everything as they track various ...parameters in the society and send them to the cloud for analysis, forecast, or learning. With the many parameters to sense, sensors are becoming complex and difficult to manufacture. To reduce the complexity of manufacturing, one can instead create advanced functional materials that react to multiple stimuli. To this end, conducting polymer aerogels are promising materials as they combine elasticity and sensitivity to pressure and temperature. However, the challenge is to read independently pressure and temperature output signals without cross‐talk. Here, a strategy to fully decouple temperature and pressure reading in a dual‐parameter sensor based on thermoelectric polymer aerogels is demonstrated. It is found that aerogels made of poly(3,4‐ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) can display properties of semiconductors lying at the transition between insulator and semimetal upon exposure to high boiling point polar solvents, such as dimethylsulfoxide (DMSO). Importantly, because of the temperature‐independent charge transport observed for DMSO‐treated PEDOT‐based aerogel, a decoupled pressure and temperature sensing can be achieved without cross‐talk in the dual‐parameter sensor devices.
A dual‐parameter sensor based on thermoelectric polymer aerogel with fully decoupled temperature and pressure sensing capability is successfully developed and characterized. This is achieved by finely tuning the transport properties of the conducting aerogels with exposure to the vapor of high boiling point polar solvents, such as dimethyl sulfoxide (DMSO). Pressure sensitivity is also improved by DMSO treatment.
Measuring temperature and heat flux is important for regulating any physical, chemical, and biological processes. Traditional thermopiles can provide accurate and stable temperature reading but they ...are based on brittle inorganic materials with low Seebeck coefficient, and are difficult to manufacture over large areas. Recently, polymer electrolytes have been proposed for thermoelectric applications because of their giant ionic Seebeck coefficient, high flexibility and ease of manufacturing. However, the materials reported to date have positive Seebeck coefficients, hampering the design of ultra-sensitive ionic thermopiles. Here we report an "ambipolar" ionic polymer gel with giant negative ionic Seebeck coefficient. The latter can be tuned from negative to positive by adjusting the gel composition. We show that the ion-polymer matrix interaction is crucial to control the sign and magnitude of the ionic Seebeck coefficient. The ambipolar gel can be easily screen printed, enabling large-area device manufacturing at low cost.
The communication outposts of the emerging Internet of Things are embodied by ordinary items, which desirably include all-printed flexible sensors, actuators, displays and akin organic electronic ...interface devices in combination with silicon-based digital signal processing and communication technologies. However, hybrid integration of smart electronic labels is partly hampered due to a lack of technology that (de)multiplex signals between silicon chips and printed electronic devices. Here, we report all-printed 4-to-7 decoders and seven-bit shift registers, including over 100 organic electrochemical transistors each, thus minimizing the number of terminals required to drive monolithically integrated all-printed electrochromic displays. These relatively advanced circuits are enabled by a reduction of the transistor footprint, an effort which includes several further developments of materials and screen printing processes. Our findings demonstrate that digital circuits based on organic electrochemical transistors (OECTs) provide a unique bridge between all-printed organic electronics (OEs) and low-cost silicon chip technology for Internet of Things applications.
Ladder‐type “torsion‐free” conducting polymers (e.g., polybenzimidazobenzophenanthroline (BBL)) can outperform “structurally distorted” donor–acceptor polymers (e.g., P(NDI2OD‐T2)), in terms of ...conductivity and thermoelectric power factor. The polaron delocalization length is larger in BBL than in P(NDI2OD‐T2), resulting in a higher measured polaron mobility. Structure–function relationships are drawn, setting material‐design guidelines for the next generation of conducting thermoelectric polymers.
The synthesis of a novel naphthalenediimide (NDI)‐bithiazole (Tz2)‐based polymer P(NDI2OD‐Tz2) is reported, and structural, thin‐film morphological, as well as charge transport and thermoelectric ...properties are compared to the parent and widely investigated NDI‐bithiophene (T2) polymer P(NDI2OD‐T2). Since the steric repulsions in Tz2 are far lower than in T2, P(NDI2OD‐Tz2) exhibits a more planar and rigid backbone, enhancing π–π chain stacking and intermolecular interactions. In addition, the electron‐deficient nature of Tz2 enhances the polymer electron affinity, thus reducing the polymer donor–acceptor character. When n‐doped with amines, P(NDI2OD‐Tz2) achieves electrical conductivity (≈0.1 S cm−1) and a power factor (1.5 µW m−1 K−2) far greater than those of P(NDI2OD‐T2) (0.003 S cm−1 and 0.012 µW m−1 K−2, respectively). These results demonstrate that planarized NDI‐based polymers with reduced donor–acceptor character can achieve substantial electrical conductivity and thermoelectric response.
A novel naphthalenediimide‐bithiazole n‐type semiconducting polymer P(NDI2OD‐Tz2) is synthesized and its structural, thin‐film morphological, as well as charge transport and thermoelectric properties are compared to the parent naphthalenediimide‐bithiophene P(NDI2OD‐T2) polymer. The new n‐type polymer has a greater backbone planarity and a reduced donor–acceptor character. N‐doped P(NDI2OD‐Tz2) can reach electrical conductivity and thermoelectric power factor far superior to those of analogous P(NDI2OD‐T2).
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