Thermoelectric Composite Films Research Articles

One Stone, Three Birds: Feasible Tuning of Barrier Heights Induced by Hybridized Interface in Free-Standing PEDOT@Bi2Te3 Thermoelectric Films.

Converting low-grade thermal energy into electrical energy is crucial for the development of modern smart wearable energy technologies. The free-standing films of PEDOT@Bi2Te3 prepared by tape-casting hold promise for flexible thermoelectric technology in self-powered sensing applications. Bi2Te3 nanosheets fabricated by the solvothermal method are tightly connected with flat-arranged PEODT molecules, forming an S-Bi bonded interface in the composite materials, and the bandgap is reduced to 1.63 eV. Compared with the PEDOT film, the mobility and carrier concentration of the composite are significantly increased at room temperature, and the conductivity reaches 684 S/cm. Meanwhile, the carrier concentration decreased sharply at 360 K indicating the creation of defect energy levels during the interfacial reaction of the composites, which increased the Seebeck coefficient. The power factor was improved by 68.9% compared to PEDOT. In addition, the introduction of Bi2Te3 nanosheets generated defects and multidimensional interfaces in the composite film, which resulted in weak phonon scattering in the conducting polymer with interfacial scattering. The thermal conductivity of the film is decreased and the ZT value reaches 0.1. The composite film undergoes 1500 bending cycles with a 14% decrease in conductivity and has good flexibility. This self-supporting flexible thermoelectric composite film has provided a research basis for low-grade thermal energy applications.

Stencil-Printed Scalable Radial Thermoelectric Device Using Sustainable Manufacturing Methods

In this study, we used n-chitosan-Bi2Te2.7Se0.3 and p-chitosan-Bi0.5Sb1.5Te3 composite inks to print a circular thermoelectric generator (TEG) device using a low-energy-input curing method. Thermoelectric (TE) composite films were fabricated using varying sizes of thermoelectric particles and a small chitosan binder (0.05 wt. %). The particles and binder were hot pressed at an applied pressure of 200 MPa and cured at 200 °C for 30 min. We achieved ZT of 0.35 for the n-type and 0.7 for the p-type TE composite films measured at room temperature. A radial TEG was fabricated using the best-performing n-type and p-type composite inks and achieved a power output of 87 µW and a power density of 727 µW/cm2 at a temperature difference of 35 K; these are among the best-reported values for printed TEG devices. Using a low-energy-input fabrication method, we eliminated the need for high-temperature and long-duration curing processes to fabricate printing devices. Thus, we envisage that the low-energy-input curing process and cost-effective printable strategy presented in this work pave the way for sustainable manufacturing of large-scale energy harvesting TEG devices.

Fabrication of flexible self-supporting black phosphorus nanosheet/PEDOT:PSS thermoelectric composite films by solution 3D printing technology

Flexible self-supporting black phosphorus/PEDOT:PSS (BP/PP) thermoelectric (TE) composite films were fabricated by a solution 3D printing technology using BP and PP as filler and matrix, respectively. When the mass content of BP is 2 wt%, a power factor of 13.18 μWm-1K-2 at 360 K was acquired for the BP/PP composite film, the related electrical conductivity and Seebeck coefficient were 755.53 S/cm and 13.21 μV/K, respectively. The resistance changing ratio for the above-mentioned BP/PP composite film was 7.5 % after bending for 500 times at a bending radius of 4 mm, indicating a good flexibility, and therefore this flexible self-supporting TE film has a wide potential for wearable electronics.

Electrochemical assembly of flexible PPy/Bi–Te alloy/PPy thermoelectric composite films with a sandwich-type structure

An array of PPy/Bi–Te/PPy nanocomposite films with a sandwich-type structure were successfully prepared through a layer-by-layer electrochemical assembly, and achieved a maximum power factor of as high as 243 ± 6 μW m−1 K−2.

High Thermoelectric Performance Related to PVDF Ferroelectric Domains in P-Type Flexible PVDF-Bi0.5Sb1.5Te3 Composite Film.

There is increasing demand to power Internet of Things devices using ambient energy sources. Flexible, low-temperature, organic/inorganic thermoelectric devices are a breakthrough next-generation approach to meet this challenge. However, these systems suffer from poor performance and expensive processing preventing wide application of the technology. In this study, by combining a ferroelectric polymer (Polyvinylidene fluoride (PVDF, β phase)) with p-type Bi0.5Sb1.5Te3 (BST) a thermoelectric composite film with maximum is produced power factor. Energy filter from ferroelectric-thermoelectric junction also leads to high Seebeck voltage ≈242µVK-1. For the first time, compelling evidence is provided that the dipole of a ferroelectric material is helping decouple electron transport related to carrier mobility and the Seebeck coefficient, to provide 5× or more improvement in thermoelectric power factor. The best composition, PVDF/BST film with BST 95wt.% has a power factor of 712µW•m-1K-2. A thermoelectric generator fabricated from a PVDF/BST film demonstrated Pmax T 12.02µW and Pdensity 40.8Wm-2 under 50K temperature difference. This development also provides a new insight into a physical technique, applicable to both flexible and non-flexible thermoelectrics, to obtain comprehensive thermoelectric performance.

Stretchable Energy Harvesting Device based on Thermoelectric Composite Films

Thermoelectric energy harvesting has attracted a lot of attention for powering self-powered devices because of the potential to generate energy anywhere with a temperature difference. In particular, a stretchable thermoelectric generator (S-TEG) can be applied to the repetitively moving parts of a machine and even a human body. Herein, we suggested a S-TEG using thermoelectric composite films made by dispersing n-type Bi2Te2.7Se0.3 powders into the polyvinylidene fluoride elastomer. The prepared n-type thermoelectric composite film with 75 wt% of Bi2Te2.7Se0.3 powders showed a power factor of 1.81 mW m−1 K−2 at room temperature. Next, we fabricated S-TEG by encapsulating thermoelectric powders-based composite films, and Ag-coated textile electrodes with an Eco-flex matrix. The fabricated stretchable energy harvester generated a maximum output power of 2.35 nW at a temperature difference (ΔT) of 25 K. By repeatedly introducing ΔT=5K, our S-TEG converted the output voltage of 3.4 mV and current signals of 0.25 mA. Moreover, a finite element analysis with multiphysics COMSOL simulation software was conducted to compare the experimental and theoretical thermoelectric output performance of the fabricated S-TEG. Finally, we demonstrated energy harvesting by converting human body heat into electrical energy for potential utilization of our energy harvester. This study led to the development of a S-TEG design using thermoelectric film with a simple and low-cost fabrication procedure, providing a potential approach for use as a next-generation wearable device power source.

Flexible free-standing BixSey@C/PEDOT:PSS thermoelectric composite film with high-performance electromagnetic interference shielding

Due to the component advantages and structural features, poly(3,4-ethylenedioxythiophene):poly(styrenesulfonic acid) (PEDOT:PSS) based inorganic–organic composite films shows huge application potential in various fields. However, there are few reports on the bi-functions of thermoelectric (TE) and electromagnetic interference (EMI) shielding for the PEDOT:PSS-based functional films. Herein, metal–organic frameworks (MOFs)-derived BixSey@C sheets with average size about ∼ 7.32 μm are obtained via the solvothermal reaction and selenization pyrolysis treatment, and then flexible free-standing BixSey@C/PEDOT: PSS (BSCP) composite films are obtained by a feasible vacuum filtration combined with cold pressing treatment, using different contents of BixSey@C content as inorganic component. Micrometer BixSey@C sheets are uniformly dispersed in the PEDOT:PSS matrix constructing bi-functional composite films with unique layered structure. When the MOFs-derived BixSey@C content is 70%, BSCP-70 composite film gets a power factor of 11.23 μW m−1 K−2 at 340 K. Meanwhile, the BSCP-70 composite film reaches the highest average total EMI shielding effectiveness (SET) value of 45.0 dB at only 41.9 μm thickness at X-band. Based on multi-physical properties of MOF-derived BixSey@C and PEDOT:PSS, flexible BixSey@C/PEDOT:PSS composite films display good application potentiality in the flexible TE devices and EMI shielding protection.

Flexible thermoelectric composite materials with self-healing ability for harvesting low-grade thermal energy

Directly converting waste heat from environment or human body into electricity without any moving parts is crucial in low-grade waste heat harvesting and wearable electronic applications. In this work, a sunlight self-healing thermoelectric generator that harvests energy from the human body is reported. Self-healing polyurethane gives the thermoelectric generators self-healing capacity, and the p/n-type thermoelectric component is composed of an organic-inorganic composite including carbon nanotubes and semiconductor nanoparticles. The ternary thermoelectric composite film exhibits a largely improved thermoelectric performance compared to the single component due to the energy-level configuration and interfacial energy filtering effect, and the power factor of self-healing p-type composite film is up to 355.6 ± 4.8 μW/(m·K2). Moreover, the healing efficiencies of the thermoelectric performance are both higher than 85% for the self-healing p-type and n-type composite films. The film-shaped thermoelectric generator, which is made up of 5 pairs of p/n-type counterparts, finally produces a voltage of 19.1 mV and power of 0.6 μW at a temperature difference of 60 K. Furthermore, a fibrous thermoelectric generator is also created and it produces a 2.1 mV open-circuit voltage and 1.39 nW power at a temperature difference between a human palm and the ambient environment.

High-performance g-C3N4 coated single-walled carbon nanotube composite films for flexible thermoelectric generators

Thermoelectric (TE) devices consisting of p-type and n-type single-walled carbon nanotubes (SWCNTs) based films, which can gather waste heat and turn it into electrical power, show potential application in supplying power for wearable electronic devices. In this study, graphitic carbon nitride (g-C3N4) has been prepared by high temperature pyrolysis of melamine and confirmed by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction pattern (XRD), respectively. Then the prepared g-C3N4 is composited with SWCNTs via mechanical mixing and vacuum-filtering method to obtain free-standing flexible g-C3N4/SWCNT thermoelectric composite films. The results demonstrate that g-C3N4 is efficiently covered on the surface of SWCNTs via interfacial π-π interaction, and g-C3N4 layer with several nanometers coated on SWCNTs simultaneously improves the electrical conductivity (σ) and the Seebeck coefficient (S) of g-C3N4/SWCNT. At a mass ratio of 2.5 % for g-C3N4/SWCNT, an optimal power factor value of 163.0 ± 1.0 μW m−1 K−2 is obtained for g-C3N4/SWCNT with the σ of 702.6 ± 1.6 S cm−1 and the S of 48.2 ± 0.2 μV K−1 at room temperature. Finally, a self-powering TE device composed of three pairs of p-n junctions is manufactured, and the actual output power is about 1.13 μW at the temperature difference of 50 K. As a result, this study offers a straightforward way to enhance the thermoelectric performance of single-walled carbon nanotubes, which can be utilized in flexible power generators.

Controlled construction of flexible thermoelectric composite films with submicron porous structure

Controlled construction of flexible thermoelectric composite films with submicron porous structure

Flexible thermoelectric Cu–Se nanowire/methyl cellulose composite films prepared via screen printing technology

Cu–Se nanowires (NWs) have been successfully synthesized by a wet chemical method and then flexible Cu–Se NW/methyl cellulose (MC) composite films have been prepared via a screen printing technology. The thermoelectric properties of the composite films were enhanced by a cold-pressing combining annealing treatment. A power factor of 121.87 μWm−1K−2 has been achieved for the Cu–Se NW/MC composite films at 380 K. A flexible thermoelectric generator (f-TEG) assembled by 4-leg of the as-prepared composite films can generate an output voltage of 0.83 mV and a maximum output power of 6.71 nW at a ΔT = 9.5 K. After being bent for 500 cycles, the resistance change ratio of the f-TEG along the strip length direction was only 3.69%, indicating that the f-TEG has a favorable stability. The screen printing process has many advantages, such as low cost, large-scale production, easy for operation, and therefore, it has a great potential for fabrication of flexible inorganic-organic thermoelectric composite films.

Energy harvesting from human body heat using highly flexible thermoelectric generator based on Bi2Te3 particles and polymer composite

Energy harvesting technology is in high demand for self-powered devices. Flexible thermoelectric generators (f-TEGs) have attracted considerable attention for application in wearable electronics, which can be applied to healthcare and smart clothing. However, previous f-TEGs still have limitations such lack of novel research focus concerning its wearable applications and complicated and high-cost fabrication procedures. This study reports an f-TEG comprising Bi2Te3-based thermoelectric composite films on a flexible substrate to demonstrate thermoelectric energy conversion from the human body. To verify the thermoelectric energy harvesting efficiency of the energy harvester based on temperature gradients, an f-TEG was developed by placing p-type Bi0.5Sb1.5Te3 (BST) of 133 μWm−1K−2 and n-type Bi2Te2.7Se0.3 (BTS) of 124 μWm−1K−2 thermoelectric films. The fabricated f-TEG harvested an output voltage of 18.13 mV, current signal of 2.74 μA, and output power of ≈ 12.6 nW at ΔT = 25 K. The theoretical thermoelectric potential distribution of the f-TEG was confirmed by finite element analysis using multiphysics simulation. Furthermore, we investigated the biological output performance of the f-TEG on the human body, which showed the output performance of ≈ 0.38 μA and ≈ 2.3 mV. This study presents the possibility of harvesting thermal energy from human body heat, which will be useful for improving wearable device applications.

Achieving high thermoelectric properties in PEDOT:PSS/SWCNTs composite films by a combination of dimethyl sulfoxide doping and NaBH4 dedoping

Incorporating single-walled carbon nanotubes (SWCNTs) can effectively optimize the thermoelectric properties of poly(3,4-ethylenedioxithiophene):poly(styrenesulfonate) (PEDOT:PSS). However, the thermoelectric performance of flexible PEDOT:PSS/SWCNTs composites is still undesired due to the contradiction between electrical conductivity (σ) and Seebeck coefficient (S). Here, we adopt dimethyl sulfoxide (DMSO) doping and NaBH4 dedoping to achieve high thermoelectric properties of PEDOT:PSS/SWCNTs composite film by simultaneously improving σ and S. The PEDOT:PSS/SWCNTs composite with 60 wt% SWCNTs exhibits the highest power factor of 411 μW m−1 K−2, originating from high σ of 1718 S cm−1 and high S of 49 μV K−1. The high σ is derived from the improved carrier transport by insulating PSS removal, the transition of PEDOT chains with ordered stacking structures, and the formed three-dimensional conductive network between PEDOT:PSS and SWCNTs. As well, the decreased carrier concentration induced by the reduction of oxidation level of PEDOT:PSS after NaBH4 dedoping leads to a compromise between σ and S. Besides, a home-made thermoelectric device, fabricated using eight pieces of as-prepared PEDOT:PSS/SWCNTs composite films, shows an output power of 391 nW at a temperature difference of 20 K. Our work indicates that the combination of DMSO doping and NaBH4 dedoping can extend to promote the thermoelectric properties of flexible thermoelectric composite films.

In-situ pulse electropolymerization of pyrrole on single-walled carbon nanotubes for thermoelectric composite materials

Electrochemical polymerization has become a powerful tool for constructing high-performance thermoelectric (TE) composite films, and attracted great attention from researchers. To date, however, there has been no report on the in-situ electrochemical polymerization of pyrrole (Py) on single-walled carbon nanotubes (SWCNTs). In this work, we developed a series of high-performance polypyrrole (PPy)/SWCNT composites by the in-situ pyrrole electropolymerization on the pre-fabricated SWCNT membrane electrode, where a pulse galvanostatic electropolymerization (PGEP) technology was adopted to perfect TE performance of the PPy/SWCNT composites via the interface engineering. As a result, the optimized PPy/SWCNT composite film achieved an excellent TE performance, with the largest power factor (PF) of 365.2 ± 9.6 μW m−1 K−2 and the maximum figure of merit (ZT) of 0.203 ± 0.005 at room temperature, which is well beyond the reach of the PPy-based binary TE composite materials reported previously. This work suggested that in-situ pulse electropolymerization would be an effective and feasible strategy for constructing high-performance TE materials, and also opened a new, promising avenue for improving TE materials in the future.

A flexible carbon fibre-based electrothermal film for fast actuation of shape memory alloy sheets

Two-dimensional shape memory alloy (SMA) structures have great potential in intelligent and highly flexible robots. However, they have challenges in direct electric heating. This paper proposes a solution to heat SMA sheets using carbon fibres as surface heat sources and indirectly transmits Joule heat generated by the carbon fibres to the SMA sheets. The preparation process of the carbon fibre-based thermoelectric composite film is illustrated in this study. The effect of heat source (carbon fibre) distribution on heat transfer characteristics and the temperature field of the SMA surface is simulated. Then, a functional prototype integrated thermoelectric film and flexible SMA is fabricated, and its effectiveness is verified by local and global activation, respectively. The results show that the composite structure can recover deformation rapidly in 2 s with only 0.7 A running current (applied to each carbon fibre). In addition, the local temperature control method can also realize distributed (spatial dimension) and sequential (temporal dimension) control of the structure. The proposed solution is expected to expand further the design and control of complex, intelligent structures with the development of 4D printing technology.

Full-Electrochemical Construction of High-Performance Polypyrrole/Tellurium Thermoelectrical Nanocomposites.

As one of the most attractive inorganics to improve the thermoelectric (TE) performance of the conducting polymers, tellurium (Te) has received intense concern due to its superior Seebeck coefficient (S). However, far less attention has been paid to polypyrrole (PPy)/Te TE composites to date. In this work, we present an innovative full-electrochemical method to architect PPy/Te TE composite films by sequentially depositing Te with large S and PPy with high electrical conductivity (σ). Consequently, the PPy/Te composite films achieved excellent TE performance, with the largest power factor (PF) reaching up to 234.3 ± 4.1 μW m-1 K-2. To the best of our knowledge, this value approaches the reported highest PF record (240.3 ± 5.0 μW m-1 K-2) for PPy-based composites. This suggests that the modified full-electrochemical method is a feasible and effective strategy for achieving high-performance TE composite films, which would probably provide a general guideline for the design and preparation of excellent TE materials in the future.

Ag2Se/nylon self-supporting composite films for wearable photo-thermoelectric generators with high output characteristics

High performance flexible Ag2Se/nylon self-supporting thermoelectric composite films were obtained. The photothermal effect of Ag2Se was introduced into the field of thermoelectricity for the first time to construct photo-thermoelectric generators.

Flexible ball-milled Bi0.4 Sb1.6 Te3/methyl cellulose thermoelectric films fabricated by screen-printing method

Flexible Bi[Formula: see text]Sb[Formula: see text]Te3 (BST)/methyl cellulose (MC) thermoelectric composite films were prepared by a two-step process: BST powders were successfully prepared via a ball milling method, and then BST/MC composite films with different volume fractions of BST were screen printed on flexible mixed cellulose esters membrane. As the contents of BST powders increased, the electrical conductivity was significantly improved, while the Seebeck coefficient was nearly unchanged, and a room temperature power factor (PF) of 2.32 [Formula: see text]W m[Formula: see text] K[Formula: see text] was achieved when the volume fraction of BST was 80%. After the cold-pressing treatment, both the electrical conductivity and Seebeck coefficient were improved, and a highest PF of 10.07 [Formula: see text]W m[Formula: see text] K[Formula: see text] was obtained at room temperature for the film with 80 vol.% BST, which was [Formula: see text]4.3 times higher than that of the pristine sample (2.32 [Formula: see text]W m[Formula: see text] K[Formula: see text] at room temperature). The tendency of thermoelectric performance varying with BST proportion was explained by the percolation threshold theory. This work shows the great potential of screen-printing technology in flexible and wearable electronics.

High-performance PANI-coated Ag2Se nanowire and PVDF thermoelectric composite film for flexible energy harvesting

Herein, polyaniline-coated silver selenide nanowire/polyvinylidene fluoride (PANI-Ag2Se/PVDF) composite are synthesized using simple approach and their application to flexible thermoelectric (TE) film are demonstrated. The TE power factor of PANI-Ag2Se filler was analyzed with various coating cycle of PANI, which was considered by carrier transport properties. For the composite film with 65 wt% of NWs an optimized power factor of ~ 196.6 μW/m K2 is obtained at 300 K. After bending for 1000 cycles, only ~ 8% of the initial power factor is decreased, exhibiting a flexibility. A 6-leg TE device assembled with the synthesized composite film, and this device generated ~ 15.4 mV and a maximum power of ~ 835.8 nW at a temperature difference (∆T) of ~ 30 K. Additionally, this flexible TE device displays a power density of ~ 2.33 W/m2 at same ∆T. This study can guide the manufacturing of high-performance flexible TE composite films consisting of inorganic/organic hybrid materials.

High performance scalable and cost-effective thermoelectric devices fabricated using energy efficient methods and naturally occuring materials

Various printing methods have recently been employed to manufacture thermoelectric generators. While providing a scalable alternative to manufacturing thermoelectric generators, these printing techniques consume excessive energy by using long-duration and high-temperature sintering to reduce the interfacial connections and grain boundaries between thermoelectric particles. We report an inexpensive and energy-saving technique for fabricating thermoelectric generator devices that can be employed for low-waste heat applications. This technique involves a synergistic approach, using a small amount of binder (0.05 wt%), a heterogenous distribution of thermoelectric particles of varying size, low temperature (120 °C) and short duration (30 min) curing, and application of uniaxial mechanical pressure (200 MPa) to reduce the grain boundaries and interfacial connection and to enhance electrical conductivity of thermoelectric composite films and thermoelements. In this work, we present a thermoelectric prototype fabricated on gold-coated Kevlar substrate using p-type chitosan-100 mesh Bi0.5Sb1.5Te3 and n-type chitosan-100 mesh Bi composite inks. The dimension of a single thermoelement was 6.5 mm × 2.3 mm × 150 µm. The 9-couple planar device was able to produce a power output of 73 µW at a voltage of 26 mV, and at a current of 2.8 mA at a temperature difference of 40 K, which is sufficient to power wireless sensor devices. Using energy-efficient methods and naturally occurring materials (Bi and chitosan), this device achieved a power density of 566 µW/cm2 for a temperature difference of 40 K matching the best reported power densities of printed thermoelectric devices fabricated using high temperature and long duration.