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Affordable and versatile power sources become crucial as miniaturized electronics and sensors become more widespread. Organic thermoelectric generators (TEGs), capable of tapping into wasted heat sustainably and economically, are viewed as key enablers for powering the sensor networks of the future. Until recently, the performance of n‐type organic thermoelectric materials has severely lagged behind their p‐type counterparts. However, reports of a stable and highly conductive n‐type polymer, poly(benzodifurandione) (PBFDO), are changing this notion. Nonetheless, validation of PBFDO as a suitable ink for scalable fabrication processes and integration of the material into a scalable organic TEG have yet to be demonstrated. This work presents the development, characterization, and optimization of a PBFDO ink for use in a scalable inkjet printing process. The n‐type ink is then integrated into a screen‐printed origami‐inspired architecture, resulting in a 21‐leg PEDOT:PSS/PBFDO organic TEG capable of delivering a record‐high normalized power density among reported polymer‐based TEGs of 0.718 nW cm−2 K−2. Moreover, the module ambient stability is demonstrated for up to 90 d, while its use for potential applications in harsh environments is validated for a temperature range of ‐8 °C to 200 °C and up to 90% relative humidity, a first for organic TEGs. [ABSTRACT FROM AUTHOR]

Achieving high electrical conductivity (σ) and power factor (PF) simultaneously remains a significant challenge for n‐type organic themoelectrics (OTEs). Herein, we demonstrate the state‐of‐the‐art OTEs performance through blending a fused bithiophene imide dimer‐based polymer f‐BTI2g‐SVSCN and its selenophene‐substituted analogue f‐BSeI2g‐SVSCN with a julolidine‐functionalized benzimidazoline n‐dopant JLBI, vis‐à‐vis when blended with commercially available n‐dopants TAM and N‐DMBI. The advantages of introducing a more lipophilic julolidine group into the dopant structure of JLBI are evidenced by the enhanced OTEs performance that JLBI‐doped films show when compared to those doped with N‐DMBI or TAM. In fact, thanks to the enhanced intermolecular interactions and the lower‐lying LUMO level enabled by the increase of selenophene content in polymer backbone, JLBI‐doped films of f‐BSeI2g‐SVSCN exhibit a unprecedent σ of 206 S cm−1 and a PF of 114 μW m−1 K−2. Interestingly, σ can be further enhanced up to 326 S cm−1 by using TAM dopant as a consequence of its favorable diffusion behavior into densely packed crystalline domains. These values are the highest to date for solution‐processed molecularly n‐doped polymers, demonstrating the effectiveness of the polymer‐dopant matching approach carried out in this work. [ABSTRACT FROM AUTHOR]

The development of n‐type organic thermoelectric materials, especially π‐conjugated small molecules, lags far behind their p‐type counterparts, due primarily to the scarcity of efficient electron‐transporting molecules and the typically low electron affinities of n‐type conjugated molecules that leads to inefficient n‐doping. Herein, the n‐doping of two functionalized (carbonyl vs dicyanovinylene) indenofluorene‐based conjugated small molecules, 2,8‐bis(5‐(2‐octyldodecyl)thien‐2‐yl)indeno[1,2‐b]fluorene‐6,12‐dione (TIFDKT) and 2,2′‐(2,8‐bis(3‐alkylthiophen‐2‐yl)indeno[1,2‐b]fluorene‐6,12‐diylidene)dimalononitrile (TIFDMT) are demonstrated, with n‐type dopant N‐DMBI. While TIFDKT shows decent miscibility with N‐DMBI, it can be hardly n‐doped owing to its insufficiently low LUMO. On the other hand, TIFDMT, despite a poorer miscibility with N‐DMBI, can be efficiently n‐doped, reaching a respectable electrical conductivity of 0.16 S cm−1. Electron paramagnetic resonance measurements confirm the efficient n‐doping of TIFDMT. Based on density functional theory (DFT) calculations, the LUMO frontier orbital energy of TIFDMT is much lower, and its wave function is more delocalized compared to TIFDKT. Additionally, the polarons are more delocalized in the n‐doped TIFDMT. Remarkably, as indicated by the grazing‐incidence wide‐angle X‐ray scattering (GIWAXS), the molecular order for TIFDMT thin‐film is enhanced by n‐doping, leading to more favorable packing with edge‐on orientation and shorter π‐π stacking distances (from 3.61 to 3.36 Å). This induces more efficient charge transport in the doped state. Upon optimization, a decent thermoelectric power factor of 0.25 µWm−1K−2 is achieved for n‐doped TIFDMT. This work reveals the effect of carbonyl vs dicyanovinylene on the n‐doping efficiency, microstructure evolution upon doping and thermoelectric performance, offering a stepping stone for the future design of efficient n‐type thermoelectric molecules. [ABSTRACT FROM AUTHOR]

The thermal conductivity (κ) governs how heat propagates in a material, and thus is a key parameter that constrains the lifetime of optoelectronic devices and the performance of thermoelectrics (TEs). In organic electronics, understanding what determines κ has been elusive and experimentally challenging. Here, by measuring κ in 17 π‐conjugated materials over different spatial directions, it is statistically shown how microstructure unlocks two markedly different thermal transport regimes. κ in long‐range ordered polymers follows standard thermal transport theories: improved ordering implies higher κ and increased anisotropy. κ increases with stiffer backbones, higher molecular weights and heavier repeat units. Therein, charge and thermal transport go hand‐in‐hand and can be decoupled solely via the film texture, as supported by molecular dynamics simulations. In largely amorphous polymers, however, κ correlates negatively with the persistence length and the mass of the repeat unit, and thus an anomalous, albeit useful, behavior is found. Importantly, it is shown that for quasi‐amorphous co‐polymers (e.g., IDT‐BT) κ decreases with increasing charge mobility, yielding a 10‐fold enhancement of the TE figure‐of‐merit ZT compared to semi‐crystalline counterparts (under comparable electrical conductivities). Finally, specific material design rules for high and low κ in organic semiconductors are provided. [ABSTRACT FROM AUTHOR]

Conjugated polymers are emerging as competitive candidates for organic thermoelectrics (OTEs). However, to make the device truly pervasive, both p‐ and n‐type conjugated polymers are essential. Despite great efforts, no n‐type equivalents to the p‐type benchmark PEDOT:PSS exist to date mainly due to the low electrical conductivity (σ). Herein, a near‐amorphous n‐type conjugated polymer, namely pDFSe, is reported with high σ by achieving the synergy between charge transport and doping efficiency. The polymer pDFSe is synthesized based on an acceptor‐triad moiety of diketopyrrolopyrrole‐difluorobenzoselenadiazole‐diketopyrrolopyrrole (DFSe), which has the noncovalently‐fused‐ring structure to reinforce the backbone rigidity. Furthermore, an axisymmetric thiophene‐selenophene‐thiophene donor is introduced, which enables the formation of near‐amorphous microstructures. The above merits ensure good doping efficiency without scarifying efficient intrachain charge‐carrier transport. Thus, pDFSe‐based n‐type transistors exhibit high electron mobility up to 6.15 cm2 V−1 s−1, much higher than its reference polymer pDSe without the noncovalently‐fused‐ring structure (0.77 cm2 V−1 s−1). Further upon n‐doping, pDFSe demonstrates excellent σ of 62.6 S cm−1 and maximum power factor of 133.1 μW m−1 K−2, which are among the highest values reported for solution‐processed n‐type polymers. The results demonstrate the great potential of near‐amorphous n‐type conjugated polymers with noncovalently‐fused‐ring structure for the next‐generation OTEs. [ABSTRACT FROM AUTHOR]

The surge in the number of distributed microelectronics and sensors requires versatile, scalable, and affordable power sources. Heat‐harvesting organic thermoelectric generators (TEGs) are regarded as potential key components of the future energy landscape. Recent advances in the performance of organic thermoelectric materials have made practical applications of organic TEGs more feasible than ever before, yet the challenges of designing and fabricating organic TEGs suitable for real scenarios are scarcely addressed. Specifically, small sensors and wearables demand for micro‐thermoelectric generators (µTEGs) with high power density architectures and small form factors, while typical demonstrations of organic TEGs are characterized by < 10 thermocouples (TCs) per cm2. This work presents a rolled, organic µTEG architecture combining large‐area, solution‐based deposition techniques, such as inkjet and spray‐coating, and an ultrathin parylene substrate to achieve a thermocouple density of 1842 TCs cm−2. Such demonstrative µTEG reaches a thermoelectric conversion performance of 0.15 µW cm−2 at ΔT = 50 K. Such power output is well in line with finite element method simulations, which highlight the benefit of the architecture and show that remarkable power densities, in the mW cm−2 range at ΔT = 10 K, are realistically achievable with geometrical improvements and already ongoing advancements in organic thermoelectric inks. [ABSTRACT FROM AUTHOR]

Wearable electronic devices have emerged as a pivotal technology in healthcare and artificial intelligence robots. Among the materials that are employed in wearable electronic devices, organic thermoelectric materials possess great application potential due to their advantages such as flexibility, easy processing ability, no working noise, being self-powered, applicable in a wide range of scenarios, etc. However, compared with classic conductive materials and inorganic thermoelectric materials, the research on organic thermoelectric materials is still insufficient. In order to improve our understanding of the potential of organic thermoelectric materials in wearable electronic devices, this paper reviews the types of organic thermoelectric materials and composites, their assembly strategies, and their potential applications in wearable electronic devices. This review aims to guide new researchers and offer strategic insights into wearable electronic device development. [ABSTRACT FROM AUTHOR]

The general strategy for n‐type organic thermoelectric is to blend n‐type conjugated polymer hosts with small molecule dopants. In this work, all‐polymer n‐type thermoelectric is reported by dissolving a novel n‐type conjugated polymer and a polymer dopant, poly(ethyleneimine) (PEI), in alcohol solution, followed by spin‐coating to give polymer host/polymer dopant blend film. To this end, an alcohol‐soluble n‐type conjugated polymer is developed by attaching polar and branched oligo (ethylene glycol) (OEG) side chains to a cyano‐substituted poly(thiophene‐alt‐co‐thiazole) main chain. The main chain results in the n‐type property and the OEG side chain leads to the solubility in hexafluorineisopropanol (HFIP). In the polymer host/polymer dopant blend film, the Coulombic interaction between the dopant counterions and the negatively charged polymer chains is reduced and the ordered stacking of the polymer host is preserved. As a result, the polymer host/polymer dopant blend exhibits the power factor of 36.9 µW m−1 K−1, which is one time higher than that of the control polymer host/small molecule dopant blend. Moreover, the polymer host/polymer dopant blend shows much better thermal stability than the control polymer host/small molecule dopant blend. This research demonstrates the high performance and excellent stability of all‐polymer n‐type thermoelectric. [ABSTRACT FROM AUTHOR]

Functionally graded materials (FGMs) are widely explored in the context of inorganic thermoelectrics, but not yet in organic thermoelectrics. Here, the impact of doping gradients on the thermoelectric properties of a chemically doped conjugated polymer is studied. The in‐plane drift of counterions in moderate electric fields is used to create lateral doping gradients in films composed of a polythiophene with oligoether side chains, doped with 2,3,5,6‐tetrafluoro‐tetracyanoquinodimethane (F4TCNQ). Raman microscopy reveals that a bias voltage of as little as 5 V across a 50 µm wide channel is sufficient to trigger counterion drift, resulting in doping gradients. The effective electrical conductivity of the graded channel decreases with bias voltage, while an overall increase in Seebeck coefficient is observed, yielding an up to eight‐fold enhancement in power factor. Kinetic Monte Carlo simulations of graded films explain the increase in power factor in terms of a roll‐off of the Seebeck coefficient at high electrical conductivities in combination with a mobility decay due to increased Coulomb scattering at high dopant concentrations. Therefore, the FGM concept is found to be a way to improve the thermoelectric performance of not yet optimally doped organic semiconductors, which may ease the screening of new materials as well as the fabrication of devices. [ABSTRACT FROM AUTHOR]

Comprehensive Summary: The investigation of n‐type doping holds a significant interest for the application of thermoelectrics. Herein, the doping of an indandione‐terminated compound Q‐4F with a singlet open‐shell ground state was studied using two n‐dopants N‐DMBI and LCV. Both of these two dopants can effectively dope Q‐4F due to the large offset between the singly occupied molecular orbital (SOMO) of dopants and the lowest unoccupied molecular orbital (LUMO) of Q‐4F. N‐DMBI has a higher doping ability than LCV as demonstrated by the UV‐vis‐NIR and EPR measurements. However, in comparison to N‐DMBI doped Q‐4F, LCV doped system exhibits much higher electrical conductivity and power factor due to its unperturbed molecular packing and favorable morphology after doping. The optimal conductivity of LCV doped Q‐4F is 7.16 × 10–2 ± 0.16 S·cm–1 and the highest power factor reaches 12.3 ± 0.85 μW·m–1·K–2. These results demonstrate that the modulation of n‐dopants is a powerful strategy to balance the doping efficiency and microstructure toward a maximum thermoelectric performance. [ABSTRACT FROM AUTHOR]

Comprehensive Summary: The investigation of n‐type doping holds a significant interest for the application of thermoelectrics. Herein, the doping of an indandione‐terminated compound Q‐4F with a singlet open‐shell ground state was studied using two n‐dopants N‐DMBI and LCV. Both of these two dopants can effectively dope Q‐4F due to the large offset between the singly occupied molecular orbital (SOMO) of dopants and the lowest unoccupied molecular orbital (LUMO) of Q‐4F. N‐DMBI has a higher doping ability than LCV as demonstrated by the UV‐vis‐NIR and EPR measurements. However, in comparison to N‐DMBI doped Q‐4F, LCV doped system exhibits much higher electrical conductivity and power factor due to its unperturbed molecular packing and favorable morphology after doping. The optimal conductivity of LCV doped Q‐4F is 7.16 × 10–2 ± 0.16 S·cm–1 and the highest power factor reaches 12.3 ± 0.85 μW·m–1·K–2. These results demonstrate that the modulation of n‐dopants is a powerful strategy to balance the doping efficiency and microstructure toward a maximum thermoelectric performance. [ABSTRACT FROM AUTHOR]

Molecular doping of conjugated polymers (CPs) is critical to improve their electrical properties in organic thermoelectric materials, which are promising candidates for low‐temperature energy harvesting and self‐powered sensors. Because excessive dopants are used in the doping process, securing highly crystalline CPs by suppressing dopant‐induced disorder is crucial. Recently, tris(pentafluorophenyl)borane (BCF) has attracted interest as a strong Brønsted acid dopant that enables efficient integer charge transfer by forming a complex with water. However, the crystalline ordering of BCF‐doped CPs has not been properly controlled; the resultant thermoelectric performance is therefore still lower than other p‐doped CPs prepared by conventional redox doping. Here, an efficient doping strategy is proposed with BCF to attain highly doped CPs with dramatically suppressed structural and energetic disorder. In a non‐polar aliphatic solvent, hexane, BCF can effectively diffuse into poly[2,5‐bis(3‐tetradecylthiophen‐2‐yl)thieno[3,2‐b]thiophene] (PBTTT) via sequential doping, leading to remarkable electrical conductivity and power factor of 230 S cm−1 and 140 µW m−1 K−2, respectively. In addition, sequentially doped films exhibit highly delocalized transport characteristics owing to the low degree of charge carrier localization within their high solid‐state ordering. The results provide an approach for disorder‐tolerant doping strategies with a systematic investigation of structure–property relationships in highly doped CPs. [ABSTRACT FROM AUTHOR]

Abstract The general strategy for n‐type organic thermoelectric is to blend n‐type conjugated polymer hosts with small molecule dopants. In this work, all‐polymer n‐type thermoelectric is reported by dissolving a novel n‐type conjugated polymer and a polymer dopant, poly(ethyleneimine) (PEI), in alcohol solution, followed by spin‐coating to give polymer host/polymer dopant blend film. To this end, an alcohol‐soluble n‐type conjugated polymer is developed by attaching polar and branched oligo (ethylene glycol) (OEG) side chains to a cyano‐substituted poly(thiophene‐alt‐co‐thiazole) main chain. The main chain results in the n‐type property and the OEG side chain leads to the solubility in hexafluorineisopropanol (HFIP). In the polymer host/polymer dopant blend film, the Coulombic interaction between the dopant counterions and the negatively charged polymer chains is reduced and the ordered stacking of the polymer host is preserved. As a result, the polymer host/polymer dopant blend exhibits the power factor of 36.9 µW m−1 K−1, which is one time higher than that of the control polymer host/small molecule dopant blend. Moreover, the polymer host/polymer dopant blend shows much better thermal stability than the control polymer host/small molecule dopant blend. This research demonstrates the high performance and excellent stability of all‐polymer n‐type thermoelectric.

Developing polymers with high electrical conductivity (σ) after n‐doping is a great challenge for the advance of the field of organic thermoelectrics (OTEs). Herein, we report a series of thiazole imide‐based n‐type polymers by gradually increasing selenophene content in polymeric backbone. Thanks to the strong intramolecular noncovalent N⋅⋅⋅S interaction and enhanced intermolecular Se⋅⋅⋅Se interaction, with the increase of selenophene content, the polymers show gradually lowered LUMOs, more planar backbone, and improved film crystallinity versus the selenophene‐free analogue. Consequently, polymer PDTzSI−Se with the highest selenophene content achieves a champion σ of 164.0 S cm−1 and a power factor of 49.0 μW m−1 K−2 in the series when applied in OTEs after n‐doping. The σ value is the highest one for n‐type donor‐acceptor OTE materials reported to date. Our work indicates that selenophene substitution is a powerful strategy for developing high‐performance n‐type OTE materials and selenophene incorporated thiazole imides offer an excellent platform in enabling n‐type polymers with high backbone coplanarity, deep‐lying LUMO and enhanced mobility/conductivity. [ABSTRACT FROM AUTHOR]

Abstract The introduction of alkoxy side chains into the backbone of conjugated polymers is an effective way to change their properties. While the impact on the structure and optoelectronic properties of polymer thin films was well‐studied in organic solar cells and transistors, limited research has been conducted on their effects on doping and thermoelectric properties. In this study, the effects of methoxy functionalization of conjugated backbones on the doping and thermoelectric properties are investigated through a comparative study of diketopyrrolopyrrole‐based conjugated polymers with and without methoxy groups (P29DPP‐BTOM and P29DPP‐BT, respectively). Methoxy‐functionalization significantly enhances doping efficiency, converting undopable pairs to dopable ones. This dramatic change is attributed to the structural changes in the polymer film caused by the methoxy groups, which increases the lamellar spacing and facilitates the incorporation of dopants within the polymer crystals. Moreover, methoxy‐functionalization is advantageous in improving the Seebeck coefficient and power factor of the doped polymers, because it induces a bimodal orientational distribution in the polymer, which contributes to the increased splitting of Fermi and charge transport levels. This study demonstrates the impact of methoxy‐functionalization of a conjugated polymer on doping behavior and thermoelectric properties, providing a guideline for designing high‐performance conjugated polymers for thermoelectric applications.

Wearable electronic devices have emerged as a pivotal technology in healthcare and artificial intelligence robots. Among the materials that are employed in wearable electronic devices, organic thermoelectric materials possess great application potential due to their advantages such as flexibility, easy processing ability, no working noise, being self-powered, applicable in a wide range of scenarios, etc. However, compared with classic conductive materials and inorganic thermoelectric materials, the research on organic thermoelectric materials is still insufficient. In order to improve our understanding of the potential of organic thermoelectric materials in wearable electronic devices, this paper reviews the types of organic thermoelectric materials and composites, their assembly strategies, and their potential applications in wearable electronic devices. This review aims to guide new researchers and offer strategic insights into wearable electronic device development.

Abstract n‐Doped polymers with high electrical conductivity (σ) are still very scarce in organic thermoelectrics (OTEs), which limits the development of efficient organic thermoelectric generators. A series of fused bithiophene imide dimer‐based polymers, PO8, PO12, and PO16, incorporating distinct oligo(ethylene glycol) side‐chain to optimize σ is reported here. Three polymers show a monotonic electron mobility decrease as side‐chain size increasing due to the gradually lowered film crystallinity and change of backbone orientation. Interestingly, polymer PO12 with a moderate side‐chain size delivers a champion σ up to 92.0 S cm−1 and a power factor (PF) as high as 94.3 µW m−1 K−2 in the series when applied in OTE devices. The PF value is among the highest ones for the solution‐processing n‐doped polymers. In‐depth morphology studies unravel that the moderate crystallinity and the formation of 3D conduction channel derived from bimodal orientation synergistically contribute to high doping efficiency and large charge carrier mobility, thus resulting in high performance for the PO12‐based OTEs. The results demonstrate the great power of simple tuning of side chain in developing n‐type polymers with substantial σ for improving organic thermoelectric performance.

The interactions between counterions and electronic carriers in electrically doped semiconducting polymers are important for delocalization of charge carriers, electronic conductivity, and thermal stability. The introduction of a dianions in semiconducting polymers leads to double doping where there is one counterion for two charge carriers. Double doping minimizes structural distortions, but changes the electrostatic interactions between the carriers and counterions. Polymeric ionic liquids (PIL) with croconate dianions are helpful to investigate the role of the counterion in p‐type semiconducting polymers. PILs prevent diffusion of the cation into the semiconducting polymers during ion exchange. The redox‐active croconate dianions undergo ion exchange with doped semiconducting polymers depending on their ionization energy. Croconate dianions are found to reduce doped films of poly(3‐hexyl thiophene), but undergo ion exchange with a polythiophene with tetraethylene glycol side chains, P(g42T‐T), that has a lower ionization energy. The croconate dianion maintains crystalline order in P(g42T‐T) and leads to a lower activation energy for the electrical conductivity than PF6− counterions. The control of the doping level with croconate allows optimization of the thermoelectric performance of the semiconducting polymer. The thermal stability of the doped films of P(g42T‐T) is found to depend strongly on the nature of the counterion. [ABSTRACT FROM AUTHOR]

Doped organic semiconductors play a central role in the development of several innovative optoelectronic and energy harvesting applications. Currently, the realization of thermoelectric generators, which require both hole‐ and electron‐transporting materials with high electrical conductivity, is strongly hindered by the scarce availability of stable solution‐processable n‐dopants and their limited efficiency. Herein, the synthesis of 4‐(1,3‐dimethyl‐2,3‐dihydro‐1H‐benzimidazol‐2‐yl)‐dibenzazepine (IStBI), a novel derivative belonging to the well‐known family of the benzimidazoline compounds, is presented. The functionalization with the planarized and rigid iminostilbene substituent allows, without significantly affecting the compound electronic structure, an efficient intercalation of the dopant molecules inside the ordered regions of thin films of the benchmark n‐type polymer poly(N,N′‐bis‐2‐octyldodecylnaphthalene‐1,4,5,8‐bis‐dicarboximide‐2,6‐diyl‐alt‐5,5′‐2,2′‐bithiophene) P(NDI2OD‐T2). Consequently, a maximum electrical conductivity of (1.14 ± 0.13) × 10−2 S cm−1 is recorded, exceeding by one order of magnitude what previously achieved upon solution doping of the reference P(NDI2OD‐T2) with benzimidazoline derivatives. The thermoelectric power factor is also simultaneously increased. The findings confirm that tailoring of the dopant chemical structure to improve structural interactions with the host semiconductors can be employed as a successful strategy to achieve more effective n‐doping, helping to close the performance gap with p‐type materials. [ABSTRACT FROM AUTHOR]

n‐Type conjugated polymers (CPs) are crucial in the applications of organic electronics. Direct coupling of electron‐deficient C−H monomer via selective C−H activation, namely C−H/C−H oxidative direct arylation polycondensation (Oxi‐DArP), is an ideal approach toward such CPs. Herein, Oxi‐DArP is firstly adopted to synthesize a high‐performance n‐type CP using a newly developed monomer, i.e. 3,6‐di(thiazol‐5‐yl)‐diketopyrrolopyrrole (Tz‐5‐DPP). Tz‐5‐DPP based homopolymer PTz‐5‐DPP with a molecular weight of 22 kDa has been synthesized via Oxi‐DArP. After n‐doping, PTz‐5‐DPP films exhibited electric conductivity values up to 8 S cm−1 and power factors (PFs) up to 106 μW m−1 K−2. Notably, this PF value is the highest for n‐type polymer thermoelectric materials to date. The Oxi‐DArP synthesis and the excellent n‐type performance of the polymer make this work an important step toward the straightforward and sustainable preparation of high‐performance n‐type polymer semiconductors. [ABSTRACT FROM AUTHOR]

Molecular doping in conjugated polymers (CPs) has recently received intensive attention for its potential to achieve high electrical conductivity in organic thermoelectric materials. In particular, it affects not only the carrier density n but also the carrier mobility µ because high degree of molecular doping changes the morphological properties. Herein, the effect of molecular doping in CP thin films on the pathways and mechanisms of charge transport is investigated, which govern the µ‐n relationship. Two representative donor–acceptor type CPs with similar µ but different molecular assembly in an undoped state, that is poly[2,5‐(2‐octyldodecyl)‐3,6‐diketopyrrolopyrrole‐alt‐5,5‐(2,5‐di(thien‐2‐yl)thieno[3,2‐b]thiophene)] (DPPDTT) and indacenodithiophene‐co‐benzothiadiazole (IDTBT), are prepared. Heavy doping with iron chloride (FeCl3) induced DPPDTT with highly crystalline edge‐on orientation to increase its µ up to 19.6 cm2 V−1 s−1, whereas IDTBT with irregular intermolecular stacking showed little change in µ. It is revealed that this different µ‐n relationship is highly attributed to the initial molecular ordering of CP films. The charge transport mechanism also becomes significantly different: both coherent and incoherent transports are observed in the doped DPPDTT, whereas incoherent transport is only found in the doped IDTBT. This study suggests guidelines for enhancing charge transport of CPs under doping in terms of structural disorder. [ABSTRACT FROM AUTHOR]

Typical n‐type conjugated polymers are based on fused‐ring electron‐accepting building blocks. Herein, we report a non‐fused‐ring strategy to design n‐type conjugated polymers, i.e. introducing electron‐withdrawing imide or cyano groups to each thiophene unit of a non‐fused‐ring polythiophene backbone. The resulting polymer, n‐PT1, shows low LUMO/HOMO energy levels of −3.91 eV/−6.22 eV, high electron mobility of 0.39 cm2 V−1 s−1 and high crystallinity in thin film. After n‐doping, n‐PT1 exhibits excellent thermoelectric performance with an electrical conductivity of 61.2 S cm−1 and a power factor (PF) of 141.7 μW m−1 K−2. This PF is the highest value reported so far for n‐type conjugated polymers and this is the first time for polythiophene derivatives to be used in n‐type organic thermoelectrics. The excellent thermoelectric performance of n‐PT1 is due to its superior tolerance to doping. This work indicates that polythiophene derivatives without fused rings are low‐cost and high‐performance n‐type conjugated polymers. [ABSTRACT FROM AUTHOR]

Comprehensive Summary: Conjugated polymers (CPs) containing quinoidal units are promising in n‐type organic thermoelectric materials because of their deep‐positioned lowest unoccupied molecular orbital (LUMO) energy levels and planar conjugated backbones. Herein, three CPs have been synthesized by copolymerizing an indandione‐terminated quinoidal unit with bithiophene derivatives. Owning to the high electron affinity of the indandione‐terminated quinoidal unit, all polymers showed deep LUMO energy levels below –4.10 eV. Incorporating electron‐withdrawing substituents (F or CN) on the bithiophene comonomer can further downshift the LUMO energy levels. As a result, a more efficient n‐doping process can be realized when employing 4‐(2,3‐dihydro‐1,3‐dimethyl‐1H‐benzimidazol‐2‐ yl)‐N,N‐dimethylbenzenamine (N‐DMBI) as the dopant. Ultimately, the polymer with CN substituents delivered the best thermoelectric performance with a power factor of up to 2.14 μW·m−1·K−2, because it possessed the lowest LUMO energy level among the three CPs. This work highlights that the modulation of LUMO energy level is an effective strategy to optimize the thermoelectric performance of CPs. [ABSTRACT FROM AUTHOR]

A conjugated‐polymer‐based n‐type yarn for thermoelectric textiles is presented. Thermoelectric textile devices are intriguing power sources for wearable electronic devices. The use of yarns comprising conjugated polymers is desirable because of their potentially superior mechanical properties compared to other thermoelectric materials. While several examples of p‐type conducting yarns exist, there is a lack of polymer‐based n‐type yarns. Here, a regenerated cellulose yarn is spray‐coated with an n‐type conducting‐polymer‐based ink composed of poly(benzimidazobenzophenanthroline) (BBL) and poly(ethyleneimine) (PEI). The n‐type yarns display a bulk electrical conductivity of 8 × 10−3 S cm−1 and Seebeck coefficient of −79 µV K−1. A promising level of air‐stability for at least 13 days can be achieved by applying an additional thermoplastic elastomer coating. A prototype in‐plane thermoelectric textile, produced with the developed n‐type yarns and p‐type yarns, composed of poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)‐coated regenerated cellulose, displays a stable device performance in air for at least 4 days with an open‐circuit voltage per temperature difference of 1 mV °C−1. Evidently, polymer‐based n‐type yarns are a viable component for the construction of thermoelectric textile devices. [ABSTRACT FROM AUTHOR]

Abstract Doped organic semiconductors play a central role in the development of several innovative optoelectronic and energy harvesting applications. Currently, the realization of thermoelectric generators, which require both hole‐ and electron‐transporting materials with high electrical conductivity, is strongly hindered by the scarce availability of stable solution‐processable n‐dopants and their limited efficiency. Herein, the synthesis of 4‐(1,3‐dimethyl‐2,3‐dihydro‐1H‐benzimidazol‐2‐yl)‐dibenzazepine (IStBI), a novel derivative belonging to the well‐known family of the benzimidazoline compounds, is presented. The functionalization with the planarized and rigid iminostilbene substituent allows, without significantly affecting the compound electronic structure, an efficient intercalation of the dopant molecules inside the ordered regions of thin films of the benchmark n‐type polymer poly(N,N′‐bis‐2‐octyldodecylnaphthalene‐1,4,5,8‐bis‐dicarboximide‐2,6‐diyl‐alt‐5,5′‐2,2′‐bithiophene) P(NDI2OD‐T2). Consequently, a maximum electrical conductivity of (1.14 ± 0.13) × 10−2 S cm−1 is recorded, exceeding by one order of magnitude what previously achieved upon solution doping of the reference P(NDI2OD‐T2) with benzimidazoline derivatives. The thermoelectric power factor is also simultaneously increased. The findings confirm that tailoring of the dopant chemical structure to improve structural interactions with the host semiconductors can be employed as a successful strategy to achieve more effective n‐doping, helping to close the performance gap with p‐type materials.

Abstract A conjugated‐polymer‐based n‐type yarn for thermoelectric textiles is presented. Thermoelectric textile devices are intriguing power sources for wearable electronic devices. The use of yarns comprising conjugated polymers is desirable because of their potentially superior mechanical properties compared to other thermoelectric materials. While several examples of p‐type conducting yarns exist, there is a lack of polymer‐based n‐type yarns. Here, a regenerated cellulose yarn is spray‐coated with an n‐type conducting‐polymer‐based ink composed of poly(benzimidazobenzophenanthroline) (BBL) and poly(ethyleneimine) (PEI). The n‐type yarns display a bulk electrical conductivity of 8 × 10−3 S cm−1 and Seebeck coefficient of −79 µV K−1. A promising level of air‐stability for at least 13 days can be achieved by applying an additional thermoplastic elastomer coating. A prototype in‐plane thermoelectric textile, produced with the developed n‐type yarns and p‐type yarns, composed of poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)‐coated regenerated cellulose, displays a stable device performance in air for at least 4 days with an open‐circuit voltage per temperature difference of 1 mV °C−1. Evidently, polymer‐based n‐type yarns are a viable component for the construction of thermoelectric textile devices.

n‐Type semiconducting polymers with high thermoelectric performance remain challenging due to the scarcity of molecular design strategy, limiting their applications in organic thermoelectric (OTE) devices. Herein, we provide a new approach to enhance the OTE performance of n‐doped polymers by introducing acceptor‐acceptor (A‐A) type backbone bearing branched ethylene glycol (EG) side chains. When doped with 4‐(2,3‐dihydro‐1,3‐dimethyl‐1H‐benzimidazol‐2‐yl)‐N,N‐dimethylbenzenamine (N‐DMBI), the A‐A homopolymer PDTzTI‐TEG exhibits n‐type electrical conductivity (σ) up to 34 S cm−1 and power factor value of 15.7 μW m−1 K−2. The OTE performance of PDTzTI‐TEG is far greater than that of homopolymer PBTI‐TEG (σ=0.27 S cm−1), indicating that introducing electron‐deficient thiazole units in the backbone further improves the n‐doping efficiency. These results demonstrate that developing A‐A type polymers with EG side chains is an effective strategy to enhance n‐type OTE performance. [ABSTRACT FROM AUTHOR]

Among the molecular doping methods widely utilized to control charge carriers in organic thermoelectric (TE) devices, solution mixing is attractive for the preparation of uniform and thick TE films to obtain high output powers. However, the effects of doping behavior in solution‐state polymers on their film properties are still not well understood, particularly for donor–acceptor (D‐A) polymers, key materials for high‐performance (opto)electronic devices. Here, by preparing three D‐A polymers with engineered side chains, the aggregation effects of D‐A polymers on the doping behavior in the solution and film states are demonstrated. In a less aggregated polymer, mixing the solution with a p‐dopant leads to the Lewis complex formation, which reduces doping efficiency and power factor. However, solution mixing of aggregated polymers induces the formation of ion pairs with the dopant, resulting in power factors that are two orders of magnitude higher at 23.7 µW m−1 K−2. Doping in the film state where aggregation is induced facilitates ion‐pair formation, resulting in smaller deviation in TE properties (power factors = 9.0–16.4 µW m−1 K−2) despite differences in their ordering structures. These results provide an in‐depth understanding of efficient solution‐state doping of D‐A polymers for TEs. [ABSTRACT FROM AUTHOR]

Local thermal management has important implications regarding comfort, energy consumption, and electronic device performance/lifetime. While organic thermoelectrics have emerged as promising materials for flexible thermoelectric energy harvesting devices, their potential as Peltier cooling element has been largely overlooked. Here, micro‐thermoelectric coolers based on doped small molecule thin‐films with a fast response time (around 25 µs) which is among the fastest micro‐thermoelectric coolers reported are presented. This experimental cooling performance is supported by simulation using the finite‐element method for thermal transport. The results show that organic thermoelectrics offer great potential for flexible and wearable micro‐thermoelectric cooling applications. [ABSTRACT FROM AUTHOR]

Largely soluble tris(pentafluorophenyl)borane (BCF) has recently emerged as a promising molecular dopant for preparing highly conductive organic thermoelectrics (TEs) using a one‐step solution‐mixing method. However, the unique doping mechanisms that include both undesirable Lewis acid doping with BCF and effective Brønsted acid doping with BCF–water complexes limit its widespread applications. Herein, the feasibility of modulating the two doping mechanisms by utilizing the competitive Lewis acid–base interactions of BCF with H2O or Lewis basic groups in conjugated polymers is demonstrated. The polymer without strong Lewis basic groups undergoes Brønsted acid doping, which efficiently forms delocalized free charge carriers and leads to superior TE power factors and figures of merit of 49.6 µW m−1 K−2 and 0.061, respectively. However, the polymer with strong Lewis basic groups undergoes both doping mechanisms competitively. BCF–polymer Lewis complexes not only generate free charge carriers inefficiently, but also hinder possible Brønsted acid doping and localize charge carriers, significantly lowering the TE properties. Nevertheless, the reduced TE properties can be dramatically improved by thermally annealing the predoped polymer films because Lewis acid doping can be substantially replaced by Brønsted acid doping owing to the different thermal stabilities between the BCF–polymer and BCF–water complexes. [ABSTRACT FROM AUTHOR]

Organic thermoelectric materials have garnered considerable attention in recent years for their potential in harvesting low-grade waste heat. The exploration of efficient and sustainable energy conversion technologies has prompted a significant interest in conjugated polymers (CPs) due to their tunable chemical structures, cost-effectiveness, environmental friendliness, light-weight, mechanically flexible and stretchable, high Seebeck coefficients, and low thermal conductivities, making them promising for organic thermoelectric devices. The optimization of the power factor in organic thermoelectric devices necessitates the incorporation of doping agents, which facilitates the intentional introduction of charge carriers in order to manipulate the electrical conductivity of the CP. The present review explores the recent developments in p-type doped CP-based thermoelectric thin films, with a particular emphasis on the intricate relationship between modifications of the chemical structure and the resultant thermoelectric properties, including electrical conductivities and power factors. Furthermore, various doping strategies, including doping processing methods and dopant structure engineering, are thoroughly examined. The comprehensive analysis presented herein contributes to the collective understanding of doped CP-based thermoelectric thin films, and offers insights into potential avenues for future research and development in this dynamically evolving field. • Recent progress on doped conjugated polymer-based thin film thermoelectric devices. • Polythiophenes and donor-acceptor polymers are included. • The various p-type dopants and doping methods are discussed. • The present review focuses on the structural modifications of conjugated polymers. [ABSTRACT FROM AUTHOR]

[Display omitted] • Thermoelectric properties of F4TCNQ-doped benzodithiophene-thienothiophene copolymers. • Partial or integer charge transfer states between the polymers and dopant. • Significant influence of polymer aggregation on polymer-dopant interaction. • Correlation between the nature of charge transfer states with thermoelectric parameters. Organic thermoelectric materials have been gaining increasing interest due to their capacity to convert waste heat into electricity. This study explores the impact of doping-induced charge transfer states on the thermoelectric properties of benzodithiophene-thieno[3,2-b]thiophene-based polymers (PBDTTT) doped with 2,3,5,6-Tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ). Detailed structural, optical, and electrical analyses were conducted on two specific polymers, PBDTTT:C (P1) and PBDTTT:EFT (P2). The investigation revealed distinct doping behaviors: P1 formed a partial charge transfer (PCT) complex, whereas P2 predominantly formed an integer charge transfer (ICT) complex. This distinction is attributed to the inherent structural differences and varying aggregation capabilities of the polymers. As a result, P2 exhibited enhanced electrical conductivity and a superior thermoelectric power factor compared to P1. This study emphasizes the critical role of polymer aggregation and charge-transfer mechanisms in optimizing the thermoelectric performance of conjugated polymers. It offers valuable insights for the development of efficient thermoelectric materials and the advancement of energy conversion technologies. [ABSTRACT FROM AUTHOR]

Nickel ethenetetrathiolate (NiETT) polymers are promising n-type thermoelectric (TE) materials, but their insolubility requires the use of an inert polymer matrix to form films, which is detrimental to the TE performance. In this work, the use of thermal annealing as a post-treatment process simultaneously enhances the electrical conductivity from 6 ± 2 to 23 ± 3 S cm−1 and thermopower from −28 ± 3 to −74 ± 4 µV K−1 for NiETT/PVDF composite films. Spectroscopic characterization reveals that the underlying mechanism involves removal of residual solvent and volatile impurities (carbonyl sulfide and water) in the NiETT polymer backbone. Additionally, microscopic characterization reveals morphological changes caused by a densification of the film that improves chain packing. These effects result in a 25 × improvement in power factor from 0.5 to 12.5 µW m−1 K−2 for NiETT/PVDF films and provide insight into the composition of these coordination polymers that maintain their stability under ambient conditions.

The development of conjugated polymers with structures that are suitable for efficient molecular doping and charge transport is a key challenge in the construction of high‐performance conjugated polymer‐based thermoelectric devices. In this study, three novel conjugated polymers based on dithienopyrrole (DTP) are synthesized and their thermoelectric properties are compared. When doped with p‐dopant, a donor–acceptor type copolymer, DPP‐MeDTP, exhibits higher electrical conductivity and thermoelectric power factor compared to the other donor–donor type copolymers. The high electrical conductivity of DPP‐MeDTP compared to the other polymers originates from the high degree of backbone planarity and molecular order, which contributes to its high charge carrier mobility. In addition, the highly crystalline structure of DPP‐MeDTP is well maintained upon doping, while the crystalline order of the other polymers decreases significantly upon doping. The findings of this work not only provide insights into the design of DTP‐based conjugated polymers for thermoelectric use but also demonstrate the significance of a high degree of molecular order and structural robustness upon doping to achieve high thermoelectric performance. [ABSTRACT FROM AUTHOR]

Three p‐type thermoelectric (TE) polymers based on the indacenodithiophene moiety substituted with bis(alkylsulfanyl)methylene side‐chains (IDTS) are synthesized. The TE characteristics of IDTS‐based donor–donor' (D–D′) type PIDTSDTTT and donor–acceptor (D–A) type polymers, PIDTSBT and PIDTS2FBT are investigated. Remarkably higher electrical conductivity (σ = ≈1000 S cm−1) and power factor (PF = ≈120 μW m−1 K−2) by doping with AuCl3 are measured for PIDTSDTTT compared to D–A type polymers. The higher σ of PIDTSDTTT originates from its higher carrier concentration compared to those of PIDTSBT and PIDTS2FBT. Moreover, the facile polaron‐to‐bipolaron transition is measured, and the charge carriers are calculated to be more stable with extended delocalization in PIDTSDTTT compared to D–A polymers. The significantly higher doping stability in PIDTSDTTT can be explained in terms of the higher conduction band of bipolarons than the valence band of O2 and H2O, which blocks the facile reduction of bipolarons in air. The energetic structures of doped polaron and bipolaron states, as well as pristine TE polymers, must be carefully considered to realize efficient and stable p‐type thermoelectric polymers, where a D–D′ type structure with further enhanced carrier mobility can be considered as a potential molecular framework. [ABSTRACT FROM AUTHOR]

In this study, a wearable and highly stretchable organic thermoelectric (TE) generator with a notable power density is developed. A highly stretchable and solution-processable TE/electrode pattern is realized by stepwise-curing elastomeric and conducting network. Significant advances in the TE or electrical properties are obtained for these stretchable patterns through post-activation treatment, which creates long-range charge transport pathways without degrading pre-established elastomeric networks. The TE and electrode patterns are solution-processed to a stretchable template, so that all-stretchable TE generator is realized. The fabricated TE generator maintains 90% of its maximum TE power output at 40% stretching stress and shows a stable TE power output after 200 stretching cycles. The TE generator maintains its stretchability in highly densified patterns, as the highly stretchable TE/electrode patterns enable good stretchability with little aid of the stretchable template. So, the TE generator has a high power density of 0.32 nW cm -2 K -2 , one of the highest values among stretchable TE generators to date., (© 2024 Wiley‐VCH GmbH.)

Organic thermoelectrics (TEs) based on carbon nanotubes (CNTs) have attracted much attention with their inherent advantages, such as, earth-abundant elements, broad electronic tunability, and excellent mechanical compliance. However, the inferior TE performance and doping stability of n-type CNTs to those of p-type CNTs have been bottlenecks to establish CNT-based next-generation TEs. Herein, we report a hybrid n-doping method that improves the n-type TE performance and long-term air-stability of water-processable single-walled CNT (SWCNT) and carboxymethyl cellulose (CMC) composite. The hybrid n-doping process with polyethyleneimine (PEI) n-dopant contains primary addition and secondary immersion doping, which causes a simultaneous increase in electrical conductivity and Seebeck coefficient through efficient n-doping and surface energy filtering effect, respectively. Furthermore, the hybrid-doped films exhibit superior long-term stability by inhibiting the oxidation of SWCNT/CMC at nanoscale, which allows to ensure the initial power factor even after storing in ambient for a month. Finally, we successfully demonstrated hybrid-doped SWCNT/CMC-based TEGs with long-term stable output characteristics. This work can offer insights to develop efficient and air-stable n-type organic TE materials and devices., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Inc. All rights reserved.)

n-Type polythiophene represents a promising category of n-type polymer thermoelectric materials known for their straightforward structure and scalable synthesis. However, n-type polythiophene often suffers from a twisted backbone and poor stacking property when introducing high-density electron-withdrawing groups for a lower lowest unoccupied molecular orbital (LUMO) level, which is considered to be beneficial for n-doping efficiency. Herein, we developed two isomers of polythiophene derivatives, PTTz1 and PTTz2, by inserting thiazole units into the polythiophene backbone composed of thieno[3,4- c ]pyrrole-4,6-dione (TPD) and thiophene-3,4-dicarbonitrile (2CNT). Although PTTz1 and PTTz2 share a similar polymer skeleton, they differ in thiazole configuration, with the nitrogen atoms of the thiazole units oriented toward TPD and 2CNT, respectively. The insertion of thiazole units significantly planarizes the polythiophene backbone while largely preserving low LUMO levels. Notably, PTTz2 exhibits a more coplanar backbone and closer π-stacking compared to PTTz1, resulting in a greatly enhanced electron mobility. Both PTTz1 and PTTz2 can be easily n-doped due to their deep LUMO levels. PTTz2 demonstrates superior thermoelectric performance, with an electrical conductivity of 50.3 S cm -1 and a power factor of 23.8 μW m -1 K -2 , which is approximately double that of PTTz1. This study highlights the impact of the thiazole unit on n-type polythiophene derivatives and provides valuable guidelines for the design of high-performance n-type polymer thermoelectric materials.

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 FeCl 3 -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., (© 2024 The Authors. Small published by Wiley‐VCH GmbH.)

Thermoelectric textile devices represent an intriguing avenue for powering wearable electronics. The lack of air-stable n-type polymers has, until now, prevented the development of n-type multifilament yarns, which are needed for textile manufacturing. Here, the thermomechanical properties of the recently reported n-type polymer poly(benzodifurandione) (PBFDO) are explored and its suitability as a yarn coating material is assessed. The outstanding robustness of the polymer facilitates the coating of silk yarn that, as a result, displays an effective bulk conductivity of 13 S cm -1 , with a projected half-life of 3.2 ± 0.7 years at ambient conditions. Moreover, the n-type PBFDO coated silk yarn with a Young's modulus of E = 0.6 GPa and a strain at break of ε break = 14% can be machine washed, with only a threefold decrease in conductivity after seven washing cycles. PBFDO and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) coated silk yarns are used to fabricate two out-of-plane thermoelectric textile devices: a thermoelectric button and a larger thermopile with 16 legs. Excellent air stability is paired with an open-circuit voltage of 17 mV and a maximum output power of 0.67 µW for a temperature difference of 70 K. Evidently, PBFDO coated multifilament silk yarn is a promising component for the realization of air stable thermoelectric textile devices., (© 2024 The Author(s). Advanced Science published by Wiley‐VCH GmbH.)

Doping polymer semiconductors is a central topic in plastic electronics and especially in the design of novel thermoelectric (TE) materials. In this contribution, it has been demonstrated that doping of oriented semicrystalline P3HT thin films with the dopant tris(4‐bromophenyl)ammoniumyl hexachloroantimonate), known as magic blue (MB), helps reach charge conductivities of 3000 S cm−1 and TE power factors of 170 ± 30 μW mK−2 along the polymer chain direction. A combination of transmission electron microscopy, polarized optical absorption spectroscopy, Rutherford backscattering, and TE property measurements helps clarify the conditions necessary to achieve such high charge conductivities. A comparative study with different dopants demonstrates that the doping mechanism is intimately related to the semicrystalline structure of the polymer and whether crystalline, amorphous or both phases are doped. The highest charge mobilities are observed when the dopant MB is preferentially located in the amorphous phase of P3HT, leaving the structure of P3HT nanocrystals almost unaltered. In this case, the P3HT nanocrystals are doped from their interface with the surrounding amorphous phase. These results indicate that doping preferentially the amorphous phase of semicrystalline polymer semiconductors is an effective strategy to reduce polaron localization, enhance charge mobilities, and improve TE power factors. [ABSTRACT FROM AUTHOR]

Doping polymer semiconductors is a central topic in plastic electronics and especially in the design of novel thermoelectric (TE) materials. In this contribution, it has been demonstrated that doping of oriented semicrystalline P3HT thin films with the dopant tris(4‐bromophenyl)ammoniumyl hexachloroantimonate), known as magic blue (MB), helps reach charge conductivities of 3000 S cm−1 and TE power factors of 170 ± 30 μW mK−2 along the polymer chain direction. A combination of transmission electron microscopy, polarized optical absorption spectroscopy, Rutherford backscattering, and TE property measurements helps clarify the conditions necessary to achieve such high charge conductivities. A comparative study with different dopants demonstrates that the doping mechanism is intimately related to the semicrystalline structure of the polymer and whether crystalline, amorphous or both phases are doped. The highest charge mobilities are observed when the dopant MB is preferentially located in the amorphous phase of P3HT, leaving the structure of P3HT nanocrystals almost unaltered. In this case, the P3HT nanocrystals are doped from their interface with the surrounding amorphous phase. These results indicate that doping preferentially the amorphous phase of semicrystalline polymer semiconductors is an effective strategy to reduce polaron localization, enhance charge mobilities, and improve TE power factors. [ABSTRACT FROM AUTHOR]

A combinatorial study of the effect of in‐mixing of various guests on the thermoelectric properties of the host workhorse polymer poly[2,5‐bis(3‐tetradecylthiophen‐2‐yl)thieno[3,2‐b]thiophene] (PBTTT) is presented. Specifically, the composition and thickness for doped films of PBTTT blended with different polymers are varied. Some blends at guest weight fractions around 10–15% exhibit up to a fivefold increase in power factor compared to the reference material, leading to zT values around 0.1. Spectroscopic analysis of the charge‐transfer species, structural characterization using grazing‐incidence wide‐angle X‐ray scattering, differential scanning calorimetry, Raman, and atomic force microscopy, and Monte Carlo simulations are employed to determine that the key to improved performance is for the guest to promote long‐range electrical connectivity and low disorder, together with similar highest occupied molecular orbital levels for both materials in order to ensure electronic connectivity are combined. [ABSTRACT FROM AUTHOR]

Three lactone‐based rigid semiconducting polymers were designed to overcome major limitations in the development of n‐type organic thermoelectrics, namely electrical conductivity and air stability. Experimental and theoretical investigations demonstrated that increasing the lactone group density by increasing the benzene content from 0 % benzene (P‐0), to 50 % (P‐50), and 75 % (P‐75) resulted in progressively larger electron affinities (up to 4.37 eV), suggesting a more favorable doping process, when employing (N‐DMBI) as the dopant. Larger polaron delocalization was also evident, due to the more planarized conformation, which is proposed to lead to a lower hopping energy barrier. As a consequence, the electrical conductivity increased by three orders of magnitude, to achieve values of up to 12 S cm and Power factors of 13.2 μWm−1 K−2 were thereby enabled. These findings present new insights into material design guidelines for the future development of air stable n‐type organic thermoelectrics. [ABSTRACT FROM AUTHOR]

Organic thermoelectric materials (OTEs) are in huge demand for their flexibility and robustness in applications of internet‐of‐things, wearables, and health monitoring devices. While choices of p‐type OTEs are widespread, there is still lack of stable (in air) n‐type systems to pair. Naphthalene‐diimides (NDIs), due to the presence of the planar‐structured electron‐deficient aromatic ring offer promising electron‐deficient building blocks to construct air‐stable n‐type semiconducting devices. Herein, an amphiphile derivative (cNDI‐1) is reported for two‐dimensional supramolecular assembly, and consequently TE measurements are carried out in a fully calibrated and standardised custom‐built Seebeck (S) set‐up. Promising S values (ca. −237 μV/K in THF and ca. −195 μV/K in water) are measured with a TE power factor of ∼0.05×10−5 μW/mK2 in THF and ∼0.6×10−5 μW/mK2 in water at room temperature. The study opens up the possibility of exploring broad range of molecular design library for newer n‐type OTEs. [ABSTRACT FROM AUTHOR]

Conjugated polymer‐based block copolymers (CP‐BCPs) are an unexplored class of materials for organic thermoelectrics. Herein, the authors report on the electronic conductivity (σ) and Seebeck coefficient (α) of a newly synthesized CP‐BCP, poly(3‐hexylthiophene)‐block‐poly (oligo‐oxyethylene methacrylate) (P3HT‐b‐POEM), upon solution co‐processing with lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and subsequently vapor‐doping with a molecular dopant, 2,3,5,6‐tetrafluoro‐7,7,8,8‐tetracyanoquinodimethane (F4TCNQ). It is found that the addition of the hydrophilic block POEM greatly enhances the processability of P3HT, enabling homogeneous solution‐mixing with LiTFSI. Notably, interactions between P3HT‐b‐POEM with ionic species significantly improve molecular order and unexpectedly cause electrical oxidizing doping of P3HT block both in solution and solid‐states, a phenomenon that has not been previously observed in Li‐salt containing P3HT. Vapor doping of P3HT‐b‐POEM‐LiTFSI thin films with F4TCNQ further enhances σ and yields a thermoelectric power factor PF= α2σ of 13.0 µW m−1 K−2, which is more than 20 times higher than salt‐free P3HT‐b‐POEM sample. Through modeling thermoelectric behaviors of P3HT‐b‐POEM with the Kang‐Snyder transport model, the improvement in PF is attributed to higher electronic charge mobility originating from the enhanced molecular ordering of P3HT. The results demonstrate that solution co‐processing CP‐BCPs with a salt is a powerful method to control structure and performance of organic thermoelectric materials. [ABSTRACT FROM AUTHOR]