Organic Thermoelectrics: Materials Preparation, Performance Optimization, and Device Integration

Recent Advances in Molecular Design of Organic Thermoelectric Materials

Organic thermoelectric (TE) materials can directly convert heat to electricity, and they are emerging as new materials for energy harvesting and cooling technologies. The performance of TE materials mainly depends on the properties of materials, including the Seebeck coefficient, electrical conductivity, thermal conductivity, and thermal stability. Traditional TE materials are mostly based on low-bandgap inorganic compounds, such as bismuth chalcogenide, lead telluride, and tin selenide, while organic materials as promising TE materials are attracting more and more attention because of their intrinsic advantages, including cost-effectiveness, easy processing, low density, low thermal conductivity, and high flexibility. However, to meet the requirements of practical applications, the performance of organic TE materials needs much improvement. A variety of efforts have been made to enhance the performance of organic TE materials, including the modification of molecular structure, and chemical or electrochemical doping. In this review, we summarize recent progress in organic TE materials, and discuss the feasible strategies for enhancing the properties of organic TE materials for future energy-harvesting applications.

As two pivotal functional segments, triazine and porphyrin can be coupled to form a highly cross-linked conjugated polymer. Although the obtained conjugated polymers are almost insoluble in most so...

Energy demand and importance are increasing with the industrial development and the development of high technology in modern society. However, the global supply of energy is facing problems such as fossil energy depletion and environmental pollution, and research and interest in alternative energy are increasing. Among them, research on thermoelectricity is being actively conducted. The thermoelectric characteristics are represented by the Seebeck coefficient, electrical conductivity, and thermal conductivity at the operating temperature. This is expressed as a thermoelectric performance index (ZT). ZT appears in proportion to the electrical conductivity and Seebeck coefficient, and inversely proportional to the thermal conductivity. Thermoelectric materials are divided into inorganic thermoelectric materials and organic thermoelectric materials, both of which have advantages and disadvantages. The inorganic thermoelectric material has high thermoelectric performance, but it is highly toxic and has low electrical conductivity. On the other hand, organic thermoelectric materials have lower performance than inorganic materials they are easy to obtain and have high electrical conductivity. In this study, organic-inorganic hybrid thermoelectric material was studied by combining the advantages of each material.In this study, Te nanowires (NWs) were synthesized at 50 Co by galvanic replacement reaction. We used Si (1 0 0) wafer as substrate of NWs. The substrate was degreased with acetone and ethanol. The solution of cadmium(1M), hydrofluoric acid (HF 51.0%, 4.5M) and tellurium dioxide (TeO2, 2mM). After the reaction, the synthesized Te NWs were washed with deionized water and IPA. The prepared Te NWs reacted with solution (silver nitrate in ethylene glycol) for topotactic reaction. After the reaction, the wires are washed several times with ethanol. The hybrid TE was fabricated by coating PEDOT:PSS on Ag-Te NWs with different ethylene glycol (EG) doping.A composite thermoelectric material was manufactured using Te (inorganic thermoelectric material) and PEDOT:PSS (organic thermoelectric material). Ag-topotactic reaction was conducted to increase the electrical conductivity of NWs. As the EG doping concentration of PEDOT increased, the electrical conductivity because the layer of PEDOT:PSS became thinner and didn’t fill the gap of NWS sufficiently. In conclusion, the Te NWs coated with PEDOT:PSS with 10% EG doping showed the best electrical conductivity and power factor. The more details will be presented. Figure 1

Simultaneous enhancement of electrical conductivity and seebeck coefficient in organic thermoelectric SWNT/PEDOT:PSS nanocomposites

Thermoelectric (TE) material, as one of new energy materials, is regarded as one of the most important energy-saving materials, which can directly achieve the interconversion between heat and electricity. Presently, inorganic semi-conductors are considered to be the best thermoelectric materials. However, the development of new thermoelectric material has attracted great attention owing to the scarce resource and limited performance of inorganic thermoelectric materials. As the discovery and wide application of conducting polymers (CPs), organic thermoelectric materials have come into the sights of people over the past 30 years. The development of CPs as a promising thermoelectric material has gained great attention over the past decades. Various CPs have been developed and investigated on thermoelectric performance such as polyacetylene (PA), polyaniline (PANi), polypyrrole (PPy), polythiophene (PTh) and their derivatives since 1989. Among numerous CPs, poly(3,4-ethylenedioxythiophene) (PEDOT) shows many superior properties compared to others due to its excellent environmental stability, water solubility, easy processibility, and high electrical conductivity, which brings new strategy for studies of high performance organic thermoelectric materials. The conductive PEDOT combined with an insulating poly(styrenesulfonate) (PSS) can form a stable aqueous PEDOT:PSS with a good film-forming property and has been regarded as one of the most potential thermoelectric material. In 2008, the thermoelectric performance of PEDOT:PSS pellets were reported systematically for the first time. Although its thermoelectric figure-of-merit ( ZT ) was as low as 10 - 3, it was one of the highest values for CPs at that time. Soon afterwards, the thermoelectric performance of the free-standing PEDOT:PSS film achieved a ZT value as high as 10 - 2 in 2010. During these years, great attention focused on the derivatives of PTh, polyselenophene (PSh), PANi, and polycarbazole (PCz). Since 2010, PEDOT:PSS has come into sight of researchers in the world. The past few years witnessed great development of thermoelectric performance of conducting PEDOT:PSS ( ZT ~10 - 1). In recent ten years, the thermoelectric figure-of-merit ( ZT ) of PEDOT has been enhanced by three orders of magnitude from 10 - 4 to 10 - 1 as one of the most promising organic thermoelectric materials. Presently, the enhanced thermoelectric performance for PEDOT concern in the increased electrical conductivity via an easy method, especially for PEDOT:PSS. A large electrical conductivity of PEDOT:PSS thin film more than 3000 S cm - 1 has been achieved by adding an organic solvent or post-treatment with organic solvents, acid, and ionic liquids. Compared to inorganic thermoelectric materials, PEDOT:PSS can achieve a high electrical conductivity without an obviously decreasing Seebeck coefficient. A further improvement of thermoelectric performance for PEDOT:PSS has been devoted to the optimization of Seebeck coefficient via the pH value adjustment, the reduction of the oxidized level of conductive PEDOT, or composite with inorganic thermoelectric materials. A large thermoelectric power factor has become a reality. Although there are large gaps from actual industrial application for thermoelectric PEDOT ( ZT ˃1), yet most efforts focus on the high performance PEDOT. A large number of new techniques and methods have been developed to improve the thermoelectric performance of PEDOT. This review pays the attention to the advantages and characteristics, development history, and performance improvement of PEDOT as a promising organic thermoelectric CP from discovery to development. In order to achieve a high performance thermoelectric PEDOT, more attention should be paid to the development of low dimensional PEDOT crystal, control of oxidized level, extension of conjugated chain length of PEDOT, new preparation method and techniques, and the effects of crystal structure on electron transport properties as well as the flexible PEDOT thermoelectric devices in the future. Additionally, it is necessary to keep up with the development of n-type organic thermoelectric materials.

In recent years, thermoelectric (TE) devices have attracted a growing attention due to their promising ability to convert waste heat into readily available electric energy. Compared to inorganic counterparts, organic TE devices emerged as the potential candidates for room-temperature and flexible (even wearable) TE power generation. During last few decades, extensive studies have been performed on the p- and n-type materials and devices to build up the inter-relationship among the TE parameters (i.e., electrical conductivity, Seebeck coefficient, thermal conductivity and power factors), demonstrating a great potential of organic TEs. In this review, recent progresses in the organic TE materials and devices, dopants and doping method, charge transport models and flexible TE device applications are summarized and the key strategies and future prospects to further optimize TE performance are discussed.

Understanding the Temperature Dependence of the Seebeck Coefficient from First-Principles Band Structure Calculations for Organic Thermoelectric Materials

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.

Thermoelectric materials with crystal-amorphicity duality induced by large atomic size mismatch

3D N-doped crumpled graphene aerogels for thermoelectric energy harvesting and highly sensitive piezoresistive sensing

Electronic structure engineering in organic thermoelectric materials

Thermoelectric (TE) materials, being capable of converting waste heat into electricity, are pivotal for sustainable energy solutions. Among emerging TE materials, organic TE materials, particularly conjugated polymers, are gaining prominence due to their unique combination of mechanical flexibility, environmental compatibility, and solution-processable fabrication. A notable candidate in this field is poly(2,5-bis(3-alkylthiophen-2-yl)thieno[3,2-b]thiophene) (PBTTT), a liquid-crystalline conjugated polymer, with high charge carrier mobility and adaptability to melt-processing techniques. Recent advancements have propelled PBTTT's figure of merit from below 0.1 to a remarkable 1.28 at 368K, showcasing its potential for practical applications. This review systematically examines strategies to enhance PBTTT's TE performance through doping (solution, vapor, and anion exchange doping), composite engineering, and aggregation state controlling. Recent key breakthroughs include ion exchange doping for stable charge modulation, multi-heterojunction architectures reducing thermal conductivity, and proton-coupled electron transfer doping for precise Fermi-level tuning. Despite great progress, challenges still persist in enhancing TE conversion efficiency, balancing or decoupling electrical conductivity, Seebeck coefficient and thermal conductivity, and leveraging melt-processing scalability of PBTTT. By bridging fundamental insights with applied research, this work provides a roadmap for advancing PBTTT-based TE materials toward efficient energy harvesting and wearable electronics.

Recent progress in thermoelectric materials

P-Type Chemical Doping-Induced High Bipolar Electrical Conductivities in a Thermoelectric Donor–Acceptor Copolymer