Highly anisotropic P3HT films with enhanced thermoelectric performance via organic small molecule epitaxy

Abstract

Conducting polymers are potential candidates for thermoelectric (TE) applications owing to their low thermal conductivity, non-toxicity and low cost. However, the coil conformation and random aggregation of polymer chains usually degrade electrical transport properties, thus deteriorating TE performance. In this work, we fabricated poly(3-hexylthiophene) (P3HT) films with highly oriented morphology using 1,3,5-trichlorobenzene (TCB), an organic small-molecule, as a template for polymer epitaxy under a temperature gradient crystallization process. The resulting P3HT molecules, which were confirmed to be highly anisotropic by a combination of scanning electron microscopy, atomic force microscopy, polarizing microscope, polarized Raman spectroscopy, and two-dimensional-grazing incidence X-ray diffraction (GIXRD) analysis, not only markedly reduced the conjugated defects along the polymer backbone, but also effectively increased the degree of electron delocalization. These combined phenomena produced an efficient, 1D path for carrier movement and therefore resulted in enhanced carrier mobility in the TCB-treated P3HT films. The maximum values of the electrical conductivity and Seebeck coefficient were 320 S cm À1 and 269 μV K À1 , respectively. Consequently, the maximum TE power factor and ZT value at 365 K reached 62.4 μW mK À2 and 0.1, respectively, in the parallel direction of the TCB-treated P3HT film. To the best of our knowledge, these are the highest values reported for pure P3HT TE materials. The method of using organic small-molecule epitaxy to generate highly anisotropic polymer films is expected to be valid for many conducting polymers.

Flexible Thermoelectric Materials and Generators: Challenges and Innovations

“…A decreased d can result in lower transport resistivity and boost σ. Stretched microstructures can also be achieved by mechanical stretching or organic small‐molecule epitaxy . Although their obtained electrical properties are still inferior to those treated by secondary doping engineering, these strategies still hold promise and should inspire future studies.…”

“…Organic small‐molecule epitaxy is also an effective strategy to enhance the structural ordering in microstructures. This process is different from the aforementioned secondary doping or mechanical stretching, because interfacial ordering effect is utilized, in which small molecules are introduced as epitaxial templates for polymer‐chain attachments . By orientating these small molecules, polymer chains are expected to be well‐oriented, resulting in an improved µ and, in turn, an improved σ .…”

“…This process is different from the aforementioned secondary doping or mechanical stretching, because interfacial ordering effect is utilized, in which small molecules are introduced as epitaxial templates for polymer‐chain attachments . By orientating these small molecules, polymer chains are expected to be well‐oriented, resulting in an improved µ and, in turn, an improved σ . Figure a shows an example of P3HT chains grown on 1,3,5‐trichlorobenzene (TCB) small‐molecular templates .…”

“…By orientating these small molecules, polymer chains are expected to be well‐oriented, resulting in an improved µ and, in turn, an improved σ . Figure a shows an example of P3HT chains grown on 1,3,5‐trichlorobenzene (TCB) small‐molecular templates . TCB powders are deposited onto the P3HT film and then melted at 348 K. By moving the glass substrate unidirectionally toward the cooling plate, a unidirectional temperature gradient is applied and the TCB is cooled down to form TCB molecular crystals.…”

Textile‐Based Thermoelectric Generators and Their Applications

“…The thermoelectric conversion efficiency of TE device dominates by the dimensionless figure of merit zT = σS 2 T / κ , where σ is the electrical conductivity, S is the Seebeck coefficient, κ is the thermal conductivity, T is the absolute temperature, and S 2 σ is the power factor, respectively. In past decades, conventional inorganic bulk‐based TE generators (TEGs) consisting of inorganic TE alloys, such as Bi 2 Te 3 , PbTe, and CoSb 3 , and thin film‐based TEGs made of inorganic TE materials, conducting polymers and derivatives, including poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), polyaniline (PANI), polypyrrole (PPy), and poly(3‐hexylthiophene) (P3HT), have been intensively investigated . However, their applications in Internet of Things and wearable electronics are still vague, because inorganic bulk‐based TEGs are rigid with inferior flexibility, while thin film‐based TEGs can only be bent in one direction.…”