Fine Art of Thermoelectricity

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Cite This: ACS Appl. Mater. Interfaces 2018, 10, 4737−4742

Fine Art of Thermoelectricity Viktor V. Brus,*,† Marc Gluba,† Jörg Rappich,† Felix Lang,† Pavlo D. Maryanchuk,‡ and Norbert H. Nickel† †

Institut für Silizium Photovoltaik, Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Berlin 12489, Germany Department of Electronics and Energy Engineering, Chernivtsi National University, Kotsubynskiy 2, Chernivtsi 58002, Ukraine

‡

S Supporting Information *

ABSTRACT: A detailed study of hitherto unknown electrical and thermoelectric properties of graphite pencil traces on paper was carried out by measuring the Hall and Seebeck effects. We show that the combination of pencil-drawn graphite and brush-painted poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) films on regular office paper results in extremely simple, low-cost, and environmentally friendly thermoelectric power generators with promising output characteristics at low-temperature gradients. The working characteristics can be improved even further by incorporating ntype InSe flakes. The combination of pencil-drawn n-InSe:graphite nanocomposites and brush-painted PEDOT:PSS increases the power output by 1 order of magnitude. KEYWORDS: pencil trace, PEDOT:PSS, paper, thermoelectricity, InSe

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INTRODUCTION Natural and artificial energy sources dissipate heat that is lost to the surrounding environment. Typically, the associated temperature gradients are too small to operate steam turbines.1−3 In contrast, thermoelectric elements enable a direct transformation of waste heat to electric power at very small temperature differences up to few degrees.4,5 Therefore, thermoelectric power generation is considered as one of the most important alternative energy sources.6 So far, the thermoelectric community is focused on bulk inorganic semiconductors, such as metal chalcogenides, for example, Bi2Te3-based materials, which are used in the most efficient and stable thermoelectric devices.7,8 These conventional thermoelectric materials are expensive, energy-consuming in preparation, and environmentally hazardous. On the other hand, conductive conjugated polymers9 and organic− inorganic hybrid nanocomposites, such as polymer/carbon nanotubes,10 turn out to be very promising materials that can be implemented in large-scale, low-cost, and flexible thermoelectric elements based on thin-film architectures. Flexible thinfilm organic thermoelectric generators open new possibilities for the development of miniature mobile and remote electronic gadgets like intelligent wireless sensors and electronic medical implants. Usually, organic semiconductors with promising thermoelectric properties exhibit p-type conductivity, for instance, poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS).11−14 Therefore, the development of new low-cost, n-type thermoelectric thin-film materials on flexible substrates is of a great practical importance. Surprisingly, an interesting © 2018 American Chemical Society

approach originates from the simple drawing with a graphite pencil on regular office paper. First, paper is cheap and decomposable. Second, paper is an insulating material and has been successfully used in electrical engineering for decades. Nowadays, paper is often considered as a flexible substrate due to recent advances in printed and drawn electronics.15,16 Despite the low electrical and thermal conductivity of paper, there are still only few reports on paper-based thin-film thermoelectric elements.17,18 The lead in a pencil is usually made of graphite powder and inorganic clay in different ratios. Pencil traces consist of a nanocomposite that contains graphite micro- and nanoparticles, multilayer nanosheets of graphene, and clay.19 The traces are electrically conductive and stable in different environments. Pencil-drawn thin films have already been implemented in different novel electronic and sensor devices, such as supercapacitors,20 terahertz generators,21 fieldeffect transistors,22 pencil-on-semiconductor photodiodes,23,24 as well as photo-, tenzo- and, chemiresistive sensors.25−29 Recently, we have proposed a novel energy-harvesting ionic− organic electronic ratchet with pencil-drawn electrodes that is capable of converting zero time-average electromagnetic noise signals within a wide range of frequencies into an useful direct current electric current for the operation of remote low-power electronics or medical implants.30 In this work, we consider the thermoelectric properties of graphite and n-InSe:graphite pencil traces. Moreover, we Received: November 16, 2017 Accepted: January 16, 2018 Published: January 16, 2018 4737

DOI: 10.1021/acsami.7b17491 ACS Appl. Mater. Interfaces 2018, 10, 4737−4742

Research Article

ACS Applied Materials & Interfaces

Figure 1. (a) Graphite pencil and PEDOT:PSS traces on regular paper; (b) morphology of the paper surface; (c, d) morphology of the pencil trance on paper; (e) Raman backscattering spectra of the pencil trace and highly oriented pyrolytic graphite as a reference; (f, g) morphology of the PEDOT:PSS trace on paper; (h) Raman backscattering spectrum of the PEDOT:PSS trace on paper (the inset shows the Raman backscattering spectrum of the bare paper).

considered as a reference. However, the pronounced D mode originates from the disordered structure of the pencil-drawn graphite film.31 The PEDOT:PSS water suspension penetrates into the paper substrate by filling voids between cellulose fibers (Figure 1b) and thus the morphology of the painted PEDOT:PSS film partially repeats the morphology of the bare paper surface (Figure 1f,g). The Raman spectrum of the PEDOT:PSS film on paper (Figure 1h) exhibits the characteristic phonon modes of the PEDOT:PSS polymer32,33 because paper is a Raman inactive material (see inset in Figure 1h). The electrical properties of the graphite and the PEDOT:PSS films on paper were investigated by Hall effect measurements using the van der Pauw geometry. The measured values of the specific electrical conductivity σ, the Hall coefficient RH, the Hall mobility μ, and the density of charge carriers n are summarized in Table 1 and compared to those of HOPG.

present a new concept of pencil trace/PEDOT:PSS thermoelectric power generators drawn and painted on regular office paper.

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RESULTS AND DISCUSSION Office paper was used as the substrate material (Figure 1a,b). The graphite films were drawn by a commercial HB pencil. The PEDOT:PSS films were painted by a paintbrush. Scanning electron microscopy (SEM) and Raman backscattering measurements were employed to inspect the morphology and structural properties of the pencil-drawn traces and PEDOT:PSS films on paper. The pencil traces on paper consist of disordered stacks of graphite flakes with different sizes (see Figure 1c,d). The G and two-dimensional (2D) modes of the Raman spectrum of the pencil trace correlate with the Raman spectrum of highly oriented pyrolytic graphite (HOPG), 4738


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ACS Applied Materials & Interfaces Table 1. Electrical Properties of the Samples under Investigation sample

σ (Ω−1 cm−1)

HOPG graphite trace pencil (HB) trace PEDOT:PSS

3.5 × 10 5.8 × 102 1.87 × 102 1.18 3

RH (cm3 C−1) −3.89 −4.14 −2.8 −6.87

× × × ×

−1

10 10−3 10−3 10−1

μ (cm2 V−1 s−1) 1362 2.44 0.53 0.67

n (cm−3) −1.6 −1.51 −2.2 −1.1

× × × ×

1019 1021 1021 1019

In case of the HOPG sample and the pencil-drawn film, a negative Hall coefficient RH is obtained reflecting electron conductance. The low value of the Hall mobility in the drawn graphite film is caused by its disordered structure (Figure 1d,c). The PEDOT:PSS film also exhibits a negative value of RH, which, however, is due to hopping transport of holes in PEDOT:PSS.34 The negative Hall coefficient in p-type PEDOT:PSS films has already been independently reported.35 The p-type conductivity of the PEDOT:PSS film on paper will be confirmed by its positive Seebeck coefficient considered below. The further analysis of the type of conductivity and thermoelectric properties of the drawn graphite and PEDOT:PSS films on paper was carried out by measuring the Seebeck coefficient S, which describes the fundamental electronic transport properties of thermoelectric materials. A schematic picture of the Seebeck effect measurement in this study is shown in Figure 2.

Figure 3. Thermoelectric voltage as a function of temperature difference for (a) pencil-drawn and (b) PEDOT:PSS traces on paper. Further, the determined Seebeck coefficients SG and SP are given for the graphite and PEDOT:PSS films, respectively.

istics of the drawn single-junction thermoelectric power generators were measuring as a function of the temperature difference between the junction and the edges of the devices, whereas the junction area was always kept at higher temperature. The I−V characteristics of the single-junction thermoelectric element measured at different temperature differences are shown in Figure 4a. As can be seen from Figure 4b,c, the main electrical characteristics, such as output power P, short-circuit current Isc, and open-circuit voltage Voc, increase with an increase of the temperature difference between the edges and the junction of the thermoelectric element. It should be mentioned that an increase of the output power can be accomplished also by making thermoelectric batteries. Two thermoelectric elements, for example, almost double the output power, are demonstrated in Figure S1 (Supporting Information). Figures 4 and S1 exhibit that pencil-drawn graphite films are capable of working in flexible low-cost thermoelectric devices. However, the thermoelectric parameters of graphite traces are still quite low and should be further improved. This can be realized by mixing graphite and layered semiconductors with ntype conductivity like InSe.36−38 Due to its layered structure, InSe can be drawn on paper in the same manner as a graphite pencil. Recently, we have shown that the drawn nanocomposite

Figure 2. Schematic representation of the Seebeck effect measurement. The experimental setup consists of two water-cooled Peltier elements with a temperature-controlled power source.

The Seebeck coefficient is determined by linear fitting of experimentally measured thermoelectric voltage ΔVt at different temperature differences across the samples S = ΔVt/ΔT (experimental details are given in Experimental Section). Figure 3a,b shows that S is negative for the graphite film and positive for the PEDOT:PSS film that indicates the electron and hole types of conductivity, respectively. It is worth noting that the measured value of the Seebeck coefficient of the pencil-drawn film on paper SG is comparable to that of other expensive electron-conducting nanocomposite materials used in flexible thermoelectric devices (−21 μV K−1).10 Thus, it is conceivable that the combination of pencil traces and PEDOT:PSS films on electrically and thermally insulating paper substrate can be used for a novel inexpensive and flexible thermoelectric device architecture. The concept of a pencil trace/PEDOT:PSS thermoelectric power generator is first realized by painting PEDOT:PSS layers over pencil traces on paper. Current−voltage (I−V) character4739


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Figure 5. Comparison of the Raman spectra of the InSe single crystal and the n-InSe:graphite-drawn film on paper.

The very low electrical conductivity of pure InSe films drawn on paper results in the negligibly low performance of thermoelectric devices based on them. Therefore, they were not considered in this study. Figure 6 shows the load I−V and output power characteristics of a single-junction n-InSe:graphite/PEDOT:PSS thermoelectric device fully drawn on paper. The short-circuit current slightly decreased; however, the open-circuit voltage significantly increased in comparison to graphite pencil traces. Consequently, the output power is increased by an order of magnitude due to the incorporation of the n-InSe flakes into the drawn graphite film, which served as the n-type film of the fully drawn hybrid organic−inorganic nInSe:graphite/PEDOT:PSS thermoelectric generator on paper. This improvement reveals a great potential of the proposed concept of the drawn thermoelectric devices for further development and wide practical applications.

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CONCLUSIONS In conclusion, we have studied the current transport and the thermoelectric properties of graphite pencil traces on paper. The Seebeck coefficient of graphite pencil-drawn films was negative and with a reasonably high value of SG = −17.5 μV K−1 comparable to other expensive electron-conducting nanocomposite materials used in flexible thermoelectric devices (−21 μV K−1).10 This allowed to draw graphite pencil trace/ PEDOT:PSS thermoelectric elements on regular office paper. The fabrication of multijunction thermoelectric power generators can be realized by drawing arrays of interconnected graphite pencil trace/PEDOT:PSS thermoelectric elements. Moreover, the n-InSe:graphite-drawn nanocomposite films exhibit a significantly higher Seebeck coefficient up to −243 μV K−1 in comparison to the graphite pencil traces. Consequently, the output power of the n-InSe:graphite/ PEDOT:PSS thermoelectric devices was increased by 1 order of magnitude to over 10 nW at the temperature difference of 50 K comparable to optimized printed silver paint/tellurium− PEDOT:PSS flexible thermoelectric generators.14 The hitherto unstudied thermoelectric properties of graphite and nanocomposite n-InSe:graphite pencil traces on paper provide new opportunities for the development of flexible, extremely simple, and cheap energy harvesters that can be used for lowtemperature waste heat sources. Our results convincingly exhibit proof-of-the concept thermoelectric devices drawn and painted on regular office paper.

Figure 4. Single-junction thermoelectric element. (a) I−V characteristics vs temperature difference. The inset shows a picture of one of the measured single-junction devices with the indication of the low (T1)and high (T2)-temperature sides. (b) Output power vs voltage at different temperature gradients. (c) Open-circuit voltage and shortcircuit current vs temperature difference.

film of graphite:layered semiconductor (GaSe) possesses a reasonable combination of the charge-transport and photoconductance properties.25 A similar approach may help to improve also the thermoelectrical properties of the drawn graphite films. A pencil lead was prepared by pressing a mixture of graphite and n-InSe powders in the mass ratio 1:1. The nanocomposite films n-InSe:graphite were also drawn on regular office paper. The Raman spectra of the InSe single crystal and the drawn nInSe:graphite film are shown in Figure 5. The peaks at 115, 178, and 227 cm−1 correspond to the 1A1g, 1 E2g, and 2A1g modes of the single-crystal InSe.39,40 The same peaks appear at the Raman spectra of the n-InSe:graphite film together with the signals from the D, G, and 2D modes of graphite. The drawn nanocomposite n-InSe:graphite films reveal a great improvement in the electron mobility and the Seebeck coefficient in comparison to the pure graphite film. However, the incorporation of InSe flakes into the drawn graphite film significantly reduces the electrical conductivity (see Table 2). 4740


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ACS Applied Materials & Interfaces Table 2. Electrical and Thermoelectrical Properties of Pencil and InSe:Graphite Traces on Paper sample

σ (Ω−1 cm−1)

pencil (HB) InSe:G

1.87 × 10 16.1

2

RH (cm3 C−1)

μ (cm2 V−1 s−1)

n (cm−3)

0.53 28.12

−2.2 × 10 −3.59 × 1018

−3

−2.8 × 10 −1.74 × 10−1

S (μV K−1)

σS2 (μW m−1 K−2)

−17.9 −243

6 95

21

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsami.7b17491. Output characteristics of two thermoelectric elements connected in series (PDF)

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Viktor V. Brus: 0000-0002-8839-124X

Figure 6. Output characteristics of the n-InSe:graphite/PEDOT:PSS thermoelectric generator at the temperature difference of 50 K.

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Author Contributions

The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript.

EXPERIMENTAL SECTION

Regular office paper with the density of 80 g m−2 was used as the substrate for all samples prepared in this study. The graphite films were drawn by a HB pencil lead with the diameter of 1 mm. The films were drawn when paper was mounted on an electronic balance. This simple approach allows controlling the applied vertical force of 1 N. The PEDOT:PSS films were painted with a paintbrush. On average, 20 μL of a commercially available PEDOT:PSS water suspension (Heraeus PH 1000) was used per square centimeter. The PEDOT:PSS layers were painted over pencil traces to prepare the thermoelectric elements. The graphite pencil-drawn and PEDOT:PSS films were 3 cm long and 5 mm wide. The painted PEDOT:PSS films were dried at room temperature and then annealed in air at 100 °C for 15 min. No additional coatings were used in this study. The area of the pencil trace/PEDOT:PSS junction was equal to ∼25 mm2. InSe crystals were grown by the Bridgman technique. The crystals possessed n-type conductivity with the electron concentration of about 1016 cm−3. InSe crystals were mechanically ground until the particle size was less than 100 μm. The prepared InSe powder was mechanically mixed with a commercially available, high-purity graphite powder (particle size ≤ 50 μm) for 20 min. The obtained InSe:graphite powder was then pressed under a pressure of 5 t cm−2 to form the composite pencil lead. Binding additives were not used in this study. The morphology and structural properties of the graphite (nInSe:graphite) and PEDOT:PSS films were examined using a scanning electron microscope (Hitachi S-4100) and a micro Raman spectrometer (LabRAM) with an excitation wavelength of 632.82 nm. The thicknesses of the graphite (n-InSe:graphite) and PEDOT:PSS films were estimated by means of a profilometer to be around 100 nm and 1.2 μm, respectively, with relative deviations ±10%. For Hall effect measurements, the van der Pauw contact geometry was used. The Hall effect measurements were carried out in air and at room temperature.41 Silver paint was taken as a contact material. Gold electrodes were deposited onto graphite (n-InSe:graphite) and PEDOT:PSS films by thermal evaporation in a vacuum chamber for the measurements of the thermoelectric properties. The Seebeck coefficient S was determined by linear fitting of experimentally measured ΔVt at different temperature differences between the contacts S = ΔVt/ΔT. The temperature difference was controlled by two thermocouples attached to the sample. Thermal paste was used to achieve good thermal contacts of the samples. The thermopower setup was calibrated by measuring silicon and indium tin oxide samples with known Seebeck coefficients.

Funding

V.V.B. acknowledges the Alexander-von-Humboldt Foundation for financial support in the framework of the Georg Forster Research Fellowship. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors are grateful to C. Klimm for taking SEM images. REFERENCES

(1) Hung, T.-C. Waste heat recovery of organic Rankine cycle using dry fluids. Energy Convers. Manage. 2001, 42, 539−553. (2) Sliwa, T.; Rosen, M. A. Natural and Artificial Methods for Regeneration of Heat Resources for Borehole Heat Exchangers to Enhance the Sustainability of Underground Thermal Storages: A Review. Sustainability 2015, 7, 13104−13125. (3) Chen, H.; Goswami, Y.; Stefanakos, E. K. A review of thermodynamic cycles and working fluids for the conversion of lowgrade heat. Renewable Sustainable Energy Rev. 2010, 14, 3059−3067. (4) Bell, L. E. Cooling, Heating, Generating Power and Recovering Waste Heat with Thermoelectric Systems. Science 2008, 321, 1457− 1451. (5) Gou, X.; Xiao, H.; Yang, S. Modeling, experimental study and optimization on low-temperature waste heat thermoelectric generator system. Appl. Energy 2010, 87, 3131−3136. (6) Liu, W.; Lie, Q.; Kim, H. S.; Ren, Z. Current progress and future challenges in thermoelectric power generation: from materials to devices. Acta Mater. 2015, 87, 357−376. (7) Han, C.; Sun, Q.; Li, Z.; Dou, S. X. Thermoelectric Enhancement of Different Kinds of Metal Chalcogenides. Adv. Energy Mater. 2016, 6, No. 1600498. (8) Luo, Y.; Yang, J.; Jiang, Q.; Li, W.; Zhang, D.; Zhou, Z.; Cheng, Y.; Ren, Y.; He, X. Progressive Regulation of Electrical and Thermal Transport Properties to High-Performance CuInTe2 Thermoelectric Materials. Adv. Energy Mater. 2016, 6, No. 1600007. (9) Russ, B.; Glaudell, A.; Urban, J. J.; Chabinyc, M. L.; Segalman, R. A. Organic thermoelectric materials for energy harvesting and temperature control. Nat. Rev. Mater. 2016, 1, No. 16050. (10) Mai, C.-K.; Russ, B.; Fronk, S. L.; Hu, N.; Chan-Park, M. B.; Urban, J. J.; Segalman, R. A.; Chabinyc, M. L.; Bazan, G. C. Varying the ionic functionalities of conjugated polyelectrolytes leads to both p-

4741


Research Article


(33) Chou, T.-R.; Chen, S.-H.; Chiang, Y.-T.; Lin, Y.-T.; Chao, C.-Y. Highly conductive PEDOT:PSS films by post-treatment with dimethyl sulfoxide for ITO-free liquid crystal display. J. Mater. Chem. C 2015, 3, 3760−3766. (34) Mott, N. F.; Devis, E. A. Electron Processes in Non-Crystalline Materials; Clarendon Press: Oxford, 1979. (35) Ozaki, S.; Wada, Y.; Noda, K. DC Hall-effect measurement for inkjet-deposited films of poly(3,4-ethylenedioxythiophene)/poly(4styrenesulfonate) by using microscale gap electrodes. Synth. Met. 2016, 215, 28−34. (36) Mudd, G. W.; Svatek, S. A.; Ren, T.; Patane, A.; Makarovsky, O.; Eaves, L.; Beton, P. H.; Kovalyuk, Z. D.; Lashkarev, G. V.; Kudrynskyi, Z. R.; Dmitriev, A. I. Tuning the Bandgap of Exfoliated InSe Nanosheets by Quantum Confinement. Adv. Mater. 2013, 25, 5714− 5718. (37) Mudd, G. W.; Svatek, S. A.; Hague, L.; Makarovsky, O.; Kudrynskyi, Z. R.; Mellor, C. J.; Beton, P. H.; Eaves, L.; Novoselov, K. S.; Kovalyuk, Z. D.; Vdovin, E. E.; Marsden, A. J.; Wilson, N. R.; Patane, A. High Broad-Band Photoresponsivity of Mechanically Formed InSe−Graphene van der Waals Heterostructures. Adv. Mater. 2015, 27, 3760−3766. (38) Bandurin, D. A.; Tyurnina, A. V.; Yu, G. L.; Mishchenko, A.; Zolyomi, V.; Morozov, S. V.; Kumar, R. K.; Gorbachev, R. V.; Kudrynskyi, Z. R.; Pezzini, S.; Kovalyuk, Z. D.; Zeitler, U.; Novoselov, K. S.; Patane, A.; Eaves, L.; Grigorieva, I. V.; Falko, V. I.; Geim, A. K.; Cao, Y. High electron mobility, quantum Hall effect and anomalous optical response in atomically thin InSe. Nat. Nanotechnol. 2017, 12, 223−227. (39) Ikari, T.; Shigetomi, S.; Hashimoto, K. Crystal Structure and Raman Spectra of InSe. Phys. Status Solidi B 1982, 111, 477−481. (40) Chen, Z.; Gacem, K.; Boukhicha, M.; Biscaras, J.; Shukla, A. Anodic bonded 2D semiconductors: from synthesis to device fabrication. Nanotechnology 2013, 24, No. 415708. (41) Brus, V. V.; Gluba, M. A.; Mai, C.-K.; Fronk, S. L.; Rappich, J.; Nickel, N. H.; Bazan, G. C. Conjugated Polyelectrolyte/Graphene Heterobilayer Nanocomposites Exhibit Temperature Switchable Type of Conductivity. Adv. Electron. Mater. 2017, 3, No. 1600515.

and n-type carbon nanotube composites for flexible thermoelectrics. Energy Environ. Sci. 2015, 8, 2341−2346. (11) Yue, R.; Xu, J. Poly(3,4-ethylenedioxythiophene) as promising organic thermoelectric materials: A mini-review. Synth. Met. 2012, 162, 912−917. (12) Wei, K.; Stedman, T.; Ge, Z.-H.; Woods, L. M.; Nolas, G. S. A synthetic approach for enhanced thermoelectric properties of PEDOT:PSS bulk composites. Appl. Phys. Lett. 2015, 107, No. 153301. (13) Fan, Z.; Du, D.; Yu, Z.; Li, P.; Xia, Y.; Ouyang, J. Significant Enhancement in the Thermoelectric Properties of PEDOT:PSS Films through a Treatment with Organic Solutions of Inorganic Salts. ACS Appl. Mater. Interfaces 2016, 8, 23204−23211. (14) Bae, E. J.; Kang, Y. H.; Jang, K.-S.; Cho, S. Y. Enhancement of Thermoelectric Properties of PEDOT:PSS and Tellurium-PEDOT:PSS Hybrid Composites by Simple Chemical Treatment. Sci. Rep. 2016, 6, No. 18805. (15) Tobjörk, D.; Osterbacka, R. Paper Electronics. Adv. Mater. 2011, 23, 1935−1961. (16) Li, Z.; Liu, H.; Ouyang, C.; Wee, W. H.; Cui, X.; Lu, T. J.; Pingguan-Murphy, B.; Li, F.; Xu, F. Recent Advances in Pen-Based Writing Electronics and their Emerging Applications. Adv. Funct. Mater. 2016, 26, 165−180. (17) Jiang, Q.; Liu, C.; Xu, J.; Lu, B.; Song, H.; Shi, H.; Yao, Y.; Zhang, L. Paper: An Effective Substrate for the Enhancement of Thermoelectric Properties in PEDOT:PSS. J. Polym. Sci., Part B: Polym. Phys. 2014, 52, 737−742. (18) Wei, Q.; Mukaida, M.; Kirihara, K.; Naitoh, Y.; Ishida, T. Polymer thermoelectric modules screen-printed on paper. RSC Adv. 2014, 4, 28802−28806. (19) Wang, Y.; Zhou, H. To draw an air electrode of a Li-air battery by pencil. Energy Environ. Sci. 2011, 4, 1704−1707. (20) Zheng, G.; Hu, L.; Wu, H.; Xie, X.; Cui, Y. Paper supercapacitors by a solvent-free drawing method. Energy Environ. Sci. 2011, 4, 3368−3373. (21) Ramakrishnan, G.; Chakkittakandy, R.; Planken, P. C. M. Terahertz generation from graphite. Opt. Express 2009, 17, 16092− 16099. (22) Kurra, N.; Kulkarni, G. U. Pencil-on-paper: electronic devices. Lab Chip 2013, 13, 2866−2873. (23) Brus, V. V.; Maryanchuk, P. D. Photosensitive Shottky-type heterojunctions prepared by the drawing of graphite films. Appl. Phys. Lett. 2014, 104, No. 173501. (24) Brus, V. V.; Maryanchuk, P. D. Graphite trace on water surface: a step toward the low-cost pencil-on-semiconductor electronics and optoelectronics. Carbon 2014, 78, 613−616. (25) Brus, V. V.; Marynchuk, P. D.; Kovalyuk, Z. D.; Abashyn, S. L. 2D nanocomposite photoconductive sensors fully dry drawn on regular paper. Nanotechnology 2015, 26, No. 255501. (26) Kang, T.-K. Tunable piezoresistive sensors based on pencil-onpaper. Appl. Phys. Lett. 2014, 104, No. 073117. (27) Lin, C.-W.; Zhao, Z.; Kim, J.; Huang, J. Pencil Drawn Strain Gauges and Chemiresistors on Paper. Sci. Rep. 2014, 4, No. 3812. (28) Frazier, K. M.; Mirica, K. A.; Walish, J. J.; Swager, T. M. Fullydrawn carbon-based chemical sensors on organic and inorganic surfaces. Lab Chip 2014, 14, 4059−4066. (29) Smith, M. K.; Jensen, K. E.; Pivak, P. A.; Mirica, K. A. Direct Self-Assembly of Conductive Nanorods of Metal-Organic Frameworks into Chemiresistive Devices on Shrinkable Polymer Films. Chem. Mater. 2016, 28, 5264−5268. (30) Brus, V. V.; Collins, S. D.; Mikhnenko, O. V.; Wang, M.; Bazan, G. C.; Nguyen, T.-Q. Fabricating Low-Cost Ionic-Organic Electronic Ratchets with Graphite Pencil and Adhesive Tape. Adv. Electron. Mater. 2016, 2, No. 1500344. (31) Tuinstra, F.; Koenig, J. L. Raman Spectrum of Graphite. J. Chem. Phys. 1970, 53, 1126−1130. (32) Chang, S. H.; Chiang, C.-H.; Kao, F.-S.; Tien, C.-L.; Wu, C.-G. Unraveling the Enhanced Electrical Conductivity of PEDOT:PSS Thin Films for ITO-Free Organic Photovoltaics. IEEE Photonics J. 2014, 6, No. 8400307. 4742


Fine Art of Thermoelectricity

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