𝝅-Conjugated donor (D)−acceptor (A) copolymers have been extensivelystudied as organic photovoltaic (OPV) donors yet remain largely unexplored in organic thermoelectrics (OTEs) despite their outstanding mechanical bendability, solution processability and flexible molecular design. Importantly, they feature high Seebeck coefficient (S) that are desirable in room-temperature wearable application scenarios under small temperature gradients. In this work, the authors have systematically investigated a series of D−A semiconducting copolymers possessing various electron-deficient A-units (e.g., BDD, TT, DPP) towards efficient OTEs. Upon p-type ferric chloride (FeCl 3 ) doping, the relationship between the thermoelectric characteristics and the electron-withdrawing ability of A-unit is largely elucidated. It is revealed that a strong D−A nature tends to induce an energetic disorder along the 𝝅-backbone, leading to an enlarged separation of the transport and Fermi levels, and consequently an increase of S. Meanwhile, the highly electron-deficient A-unit would impair electron transfer from D-unit to p-type dopants, thus decreasing the doping efficiency and electrical conductivity (𝝈). Ultimately, the peak power factor (PF) at room-temperature is obtained as high as 105.
In this work, a composite product of Mn-substituted SnTe, SnO 2 nanoparticles, and MnTe-supersaturated precipitates has been fabricated by a simple in situ reaction between SnTe and MnO 2 for the first time. Benefiting from the synergistic effect induced by the product of in situ reaction, a remarkable improvement in the thermoelectric performance has been achieved. On the one hand, Mn substitution in SnTe can effectively modify the band structure and enhance the electrical properties of SnTe; on the other hand, the thermal transport can also be dramatically suppressed by in situ reaction-derived multiscale phonon scattering by point defects, SnO 2 nanoparticles, and supersaturated MnTe precipitates. Ultimately, a maximum ZT of ∼1.5 at 873 K has been achieved in the SnTe + 10 mol % MnO 2 sample, which increases by 224% in comparison with the pristine SnTe, representing one of the best results ever reported for SnTe-based thermoelectric materials.
Carbon nanotubes (CNTs) have been demonstrated as promising candidates for thermoelectrics (TEs) owing to their excellent electrical and mechanical properties. Here a new dopant to obtain flexible n‐type CNT‐based TE films from solution is reported. By doping single‐walled carbon nanotubes (SWCNTs) with tetrabutylammonium bromide (TBAB), p‐type nanotubes can be successfully converted to n‐type form, which is confirmed by both Raman and X‐ray photoemission spectroscopy (XPS) spectra. Furthermore, the influences of doping concentration and dispersion medium on TE properties are investigated. The optimal n‐type SWCNT films fabricated in N,N‐dimethylformamide (DMF) solvent exhibit an impressive power factor of 339 µW m−1 K−2 and excellent air stability by less than 10% variation of Seebeck coefficient during 192 h at room temperature without encapsulation, both of which are among the hitherto highest reported. This work sheds light on the interaction between TBAB molecules and SWCNTs in different dispersion media and offers a guideline for efficient n‐doping of SWCNT based TE materials.
Metal halide perovskites (MHPs) hold great potential in thermoelectric (TE) applications, thanks to their regular and soft lattice in nature. However, the poor electrical conductivity caused by low charge carrier density (<1014 cm−3 for lead‐based MHPs) strongly impedes its TE development. In this scenario, tin halide perovskites (THPs) emerge as promising TE candidates owing to their high background hole densities (>1019 cm−3). However, further electrical doping remains challenging, originating from the limited capability of accommodating heterogeneous dopants and the heavy compensation in THPs. Herein, a novel diffusion‐mediated doping approach is demonstrated to prominently increase the p‐type doping level of THPs by a sequence of air exposure and 2,3,5,6‐tetrafluoro‐7,7,8,8‐tetracyanoquinodimethane (F4TCNQ) surface treatments. In paradigm photovoltaic THP materials—CH(NH2)2SnI3 (namely FASnI3), the electrical conductivity is dramatically increased by 300× from 0.06 to 18 S cm−1 in thin films, leading to a remarkable enhancement of power factor by 25× up to 53 μW m−1 K−2. In contrast, only a slight variation of thermal conductivity is observed after F4TCNQ deposition, which is in accordance with the increase in electrical conductivity, indicating that the lattice structures of FASnI3 remain intact after doping. This study paves an illuminating way to ameliorate TE properties in halide perovskites.
n-Type Co NWs/N2200 TENCs yield a high S, mainly from the semiconducting polymer, yet σ is limited by poor connectivity between inorganic and organic domains. By adding flexible n-doped SWCNTs to yield more conductive paths, σ and mechanical bendability are greatly enhanced.
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