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Table of Contents Macromolecular Research

Importance of Architectural Asymmetry for Improved Triboelectric Nanogenerators with 3D Spacer Fabrics

Jin-Hyuk Kwon, Jaebum Jeong, Youngju Lee, Swarup Biswas, Jun-Kyu Park, Suwoong Lee, Dong-Wook Lee, Sohee Lee*,Jin-Hyuk Bae*, and Hyeok Kim*

Macromol. Res., 29, 443 (2021)

Three types of triboelectric nanogenerators (TENGs) were fabricated by stacking polyester/spandex blend 3D spacer fabrics, polydimethylsiloxane (PDMS) films, and electrodes withdifferent stack configurations. The TENG with the PDMS/fabric/fabric configuration exhibitedthe highest maximum peak-to-peak output voltage (Vo,p-p) among all types. The Vo,p-p improve-ment was understood in terms of the architectural asymmetry of the device configuration.

DOI 10.1007/s13233-021-9052-1 www.springer.com/13233 pISSN 1598-5032 eISSN 2092-7673

Macromolecular Research Article

Macromol. Res., 29(6), 443-447 (2021) 443 © The Polymer Society of Korea and Springer 2021

Importance of Architectural Asymmetry for Improved Triboelectric Nanogenerators with 3D Spacer Fabrics

Abstract: We investigated the importance of architectural asymmetry to improve

the output voltage of the triboelectric nanogenerators (TENGs) with polyester/

spandex blend 3D spacer fabrics. Different types of TENGs were fabricated by stack-

ing the 3D spacer fabrics, polydimethylsiloxane (PDMS) films, and electrodes with

different stack configurations. The 3D spacer fabric TENGs fabricated with higher

architectural asymmetry exhibited higher output voltages than those fabricated

with lower architectural asymmetry. In particular, the TENG with the PDMS/fabric/

fabric configuration exhibited the highest maximum peak-to-peak output voltage

among all types. The prominent increase in the TENG output voltage was ascribed

to the relatively high architectural asymmetry in the device configuration and the

relatively high effective density of triboelectric charges.

Keywords: triboelectric nanogenerator, 3D spacer fabric, output voltage, architectural asymmetry.

1. Introduction

Over the past decade, energy harvesting has been in the spot-

light as a special concept for eco-friendly technology harnessing

environmental energy sources.1-4 Energy harvesters, devices that

convert ambient energy into a usable form of energy such as

electrical energy, are required. Among the diverse types of energy

harvesters, triboelectric nanogenerators (TENGs) have recently

attracted significant attention because of their outstanding energy

conversion efficiency and applicability to self-powered sensor

systems.5-7 In particular, fabric-based TENGs are highly compati-

ble with the human body and skin in terms of flexibility, stretchabil-

ity, and texture.8-10 Moreover, fabric-based TENGs have great potential

for excellent power generation due to their dense internal fiber-

to-fiber mechanical interaction. Accordingly, fabric-based TENGs

are one of the most promising candidates for wearable elec-

tronics.

Diverse types of fabrics, such as standard 2D woven fabrics,

3D orthogonally woven fabrics, and 3D spacer fabrics, can be

used for the TENG active layers. It is worth noting that 3D

spacer fabrics provide a better option for TENG performance

than standard 2D woven fabrics.11,12 In a previous study, 3D

spacer fabric TENGs exhibited peak-to-peak output voltage

(Vo,p-p) of approximately 240 V, whereas the standard 2D fabric

TENG yields only approximately 35 V.13 Nevertheless, the per-

formance of 3D spacer fabric TENGs needs to be maximized

through multidimensional engineering methods and approaches.

The compositional heterogeneity of constituent materials is widely

known to be a critical factor for fabricating high-performance

TENGs.14,15 Furthermore, modifying the architectural asymmetry

of the device configuration can be an important consideration

for improving the performance of 3D spacer fabric TENGs because

TENGs basically utilize the unbalanced spatial distribution of

triboelectric charges. However, the importance of asymmetric

architectures for 3D spacer fabric TENGs is not yet fully under-

stood.

In this study, we investigated the importance of architectural

asymmetry in the device configuration to enhance the output

voltage (Vo) of 3D spacer fabric TENGs. The surface and cross-

section morphologies of the 3D spacer fabric were examined

Jin-Hyuk Kwon†,1

Jaebum Jeong2

Youngju Lee3,4

Swarup Biswas4

Jun-Kyu Park3

Suwoong Lee3

Dong-Wook Lee3

Sohee Lee*,5

Jin-Hyuk Bae*,1,6

Hyeok Kim*,4

1School of Electronic and Electrical Engineering, Kyungpook National University, Daegu 41566, Korea2Nano Materials & Nano Technology Center, Korea Institute of Ceramic Engineering and Technology

(KICET), Jinju 52851, Korea3Applied Robot R&D Department, Korea Institute of Industrial Technology (KITECH), Ansan, 15588, Korea4School of Electrical and Computer Engineering, Institute of Information Technology, University of

Seoul, 163 Seoulsiripdaero, Dongdaemun-gu, Seoul 02504, Korea5Department of Clothing and Textiles, Research Institute of Natural Science, Gyeongsang National

University, 501 Jinjudaero, Jinju, Gyeongsangnamdo, 52828, Korea6School of Electronics Engineering, Kyungpook National University, Daegu 41566, Korea

Received April 2, 2021 / Revised June 2, 2021 / Accepted June 3, 2021

Acknowledgments: This research was supported by Korea ElectricPower Corporation (Grant number: R19XO01-05) and Basic ScienceResearch Program through the National Research Foundation of Korea(NRF) funded by Ministry of Education, Science and Technology (NRF-2018R1D1A3B07049551).

*Corresponding Authors: Sohee Lee ([email protected]),Jin-Hyuk Bae ([email protected]), Hyeok Kim ([email protected])†Current address: Research Institute of Printed Electronics & 3D Printing,Industry University Cooperation Foundation, Hanbat National University,Daejeon 34158, Korea.

© The Polymer Society of Korea and Springer 2021 444 Macromol. Res., 29(6), 443-447 (2021)

Macromolecular Research

using scanning electron microscopy (SEM). Moreover, the 3D

spacer fabric was observed using transmitted light microscopy

to understand its basic structure more comprehensively. Three

different types of TENGs with 3D spacer fabric were fabricated

by varying the configuration of constituent layers. The Vos of

the TENGs were characterized and compared. The different

performances of the TENGs were examined from an architec-

tural point of view.

2. Experimental

TENGs based on 3D spacer fabrics were fabricated in a sand-

wich stack configuration. Figure 1(a) shows the front and back

sheets of the 3D spacer fabric. The 3D spacer fabric was pur-

chased from PAKA INTERTEX (Seoul, South Korea). The front

and back sheets of the 3D spacer fabric had a knitted structure

with loops, that is, single jersey. Elongated 3D spacers were

present between the front and back sheets. Moreover, the 3D

spacer fabric contained 92% polyester and 8% spandex. PDMS

films were prepared using Sylgard-184, an elastomeric PDMS

kit from Dow Corning (Midland, MI, USA). A 10:1 PDMS base/

curing agent mixture was stored in a vacuum environment to

remove air bubbles and subsequently poured onto a flat plate.

The poured mixture was then baked at 100 °C for 1 h on a hot

plate. The mechanical elasticity of PDMS, a well-known elasto-

mer, matches well with the polyester/spandex blend fabric.

Moreover, copper tapes were utilized as electrodes. The thick-

nesses of the 3D spacer fabric, PDMS film, and copper electrode

were 1.68 mm, 1 mm, and 50 µm, respectively. As shown in Fig-

ure 1(b), the 3D spacer fabrics, PDMS films, and copper tape

electrodes were stacked to fabricate TENGs. Specifically, three

different types of TENGs (denoted as Types 1-3) were fabricated

by varying the configuration of constituent layers, as shown in

Figure 1(c). The TENG dimensions were 8 cm × 8 cm. Unlike

Type 1 TENG, where the fabric layer was sandwiched between

identical PDMS films (i.e., PDMS/fabric/PDMS), Type 2 (PDMS/

PDMS/fabric), and Type 3 (PDMS/fabric/fabric) TENGs were

designed to have higher architectural asymmetry in their sand-

wich stack configuration. Moreover, the bottom electrode was

in contact with a single fabric layer in the Type 1 and Type 2

TENGs, whereas the bottom electrode was sandwiched between

the top and bottom fabric layers in the Type 3 TENG. The TENG

Vos were measured under repetitive pressure application and

release using a low-noise current preamplifier (SR570; Stanford

Research Systems, Sunnyvale, CA, USA) at room temperature

(296 K) and humidity of 29% RH. The applied pressure for the

measurements was 0.156 N/cm2.

3. Results and discussion

Figures 2(a) and 2(b) show SEM images of the front and back

surfaces of the 3D spacer fabric. Basically, the front and back

surfaces had the intertwined yarns of the single-jersey weave

architecture, but there was a difference in morphology between

the front and back surfaces. The back surface had a higher den-

sity of 3D spacer loops, as shown in Figure 2(b), than the front

surface. That is, the 3D spacer fabric itself had an asymmetrical

morphology, which may induce an unbalanced spatial distribu-

tion of triboelectric charges. Figure 2(c) shows the surface SEM

image of a constituent yarn, a single strand of fibers. The numer-

ous fibers of the 3D spacer fabric are likely to interact mechani-

cally with each other under externally applied compression.

Figure 2(d) shows a surface SEM image of a single fiber. The

observed fiber exhibited an uneven and bumpy surface, which

can be a desirable morphology in TENG engineering. In addition,

Figure 2(e) shows a cross-section SEM image of the 3D spacer

Figure 1. (a) Images of the front and back sheets of the 3D-spacer fabric, (b) a schematic of the fabrication method for the 3D-spacer fabric

TENGs, PDMS film, and copper tape electrode, and (c) the three types of TENGs with different stack configurations.



fabric. The cross-section of the fabric exhibited 3D spacer fibers

vertically laid and tilted between the front and back sheets. The

3D spacer fibers, which had an elongated cylindrical structure,

were intertwined with the yarns of the front and back sheets.

The 3D spacer fabric was observed using transmitted light

microscopy to fundamentally and morphologically understand

the triboelectric charge generation in the TENGs. Figure 3(a)

shows the transmitted light microscopy image of the 3D spacer

fabric. The 3D spacer fabric exhibited highly dense microgaps

among fibers and yarns, implying their 3D spatial distribution.

The 3D distribution of inter-fiber and inter-yarn microgaps is

likely to affect the momentary motional dynamics of fibers and

the consequent spatial density of fiber-to-fiber mechanical

interactions under externally applied compression. In particular,

fiber surfaces are considered to continually interact with each

other throughout the momentary deformation process of the fabric.

Accordingly, such microgaps result in the generation of highly

dense triboelectric charges under externally applied compres-

sion. Note that the 3D spacer fabric utilized in this work was a

polyester/spandex blend fabric. The spandex-derived elasticity,

enhancing the momentary motional dynamics of the fibers, was

considered advantageous for the vigorous generation of triboelec-

tric charges. The compositional heterogeneity of the constituent

materials also contributed to the triboelectric charging in TENGs.

Figure 3(b) shows the transmitted light microscopy image for

the cross-section of the 3D spacer fabric. Highly dense microgaps

observed among 3D spacer fibers can also lead to the generation

of highly dense triboelectric charges on their surfaces under

externally applied compression. The interfaces between 3D

spacer fibers and the front (and back) sheets also can be sites of

triboelectric charge generation. In addition, the 3D spacer fibers,

acting as elastic potential energy repositories, are considered

to maximize the momentary motional dynamics of fibers. It is

important to note again that the 3D spacer fibers were inter-

twined with the yarns of the front and back sheets of the fabric.

Figures 4(a)-4(c) show the Vos of Type 1-3 TENGs, respec-

tively. The internal polarity indicated by the measured Vos of the

Type 1 TENG is possibly due to the previously mentioned mor-

Figure 2. SEM images of (a) the front sheet, (b) the back sheet, (c) a single yarn, (d) a single fiber, and (e) the cross-section of the 3D spacer fabric.

Figure 3. (a) Transmitted light microscopy image of the 3D spacer fabric and (b) that for the cross-section.

© The Polymer Society of Korea and Springer 2021 446 Macromol. Res., 29(6), 443-447 (2021)


phological asymmetry of the 3D spacer fabric itself. In contrast,

the Type 2 and 3 TENGs exhibited higher Vos than the Type 1

TENG. The higher Vos of the Type 2 and 3 TENGs can be attributed

to the relatively high architectural asymmetry of the device

configuration. Specifically, the maximum Vo,p-ps of the Type 1-3

cases were 205.0, 306.0, and 701.2 V, respectively, as shown in

Figure 4(d). Moreover, the Type 3 TENG exhibited a higher

maximum Vo,p-p than the Type 2 TENG. Unlike the Type 1 TENG,

where the bottom electrode was in contact with a single fabric

layer, the bottom electrode of the Type 3 TENG was sandwiched

between the top and bottom fabric layers. This double fabric/

electrode junction configuration increased the effective den-

sity of the triboelectric charges experienced by the electrode

surface, as shown in Figure 4(e). Herein, the effective density of

triboelectric charges is defined as the sum of the top-surface

and bottom-surface densities of the triboelectric charges expe-

rienced by the electrode, as shown in Figure 4(e). Accordingly,

the highest maximum Vo,p-p of the Type 3 TENG among all types

can be attributed to the architectural asymmetry of the device

configuration and the increased effective density of the triboelectric

charges. These results indicate that the Vo of 3D spacer fabric

TENGs can be enhanced prominently by modifying the device

configuration asymmetry and increasing the effective density

of triboelectric charges on electrode surfaces in stack architec-

tures. In further studies, complex electrostatic interactions

between charged PDMS/copper and fabric/copper interfaces

need to be investigated thoroughly for a higher level of charac-

teristic optimization.

4. Conclusions

In summary, three different types of TENGs with polyester/

spandex blend 3D spacer fabrics were fabricated by varying

the configuration of the constituent layers, and their Vos were

compared. The 3D spacer fabric exhibited numerous intertwined

yarns and fibers as well as uneven and bumpy fiber surfaces in

the SEM images. In addition, highly dense inter-fiber and inter-

yarn microgaps in the 3D spacer fabric were observed using

transmitted light microscopy to better understand the triboelec-

tric charge generation in the TENG. Most importantly, the TENGs

with PDMS/fabric/PDMS, PDMS/PDMS/fabric, and PDMS/fab-

ric/fabric configurations exhibited maximum Vo,p-ps of 205.0,

306.0, and 701.2 V, respectively. The PDMS layer in the TENGs,

which is an insulator, was employed to realize the architectural

asymmetry and unbalanced charge distribution between the

electrodes. The highest maximum Vo,p-p of the PDMS/fabric/fab-

ric TENG was attributed to the architectural asymmetry of the

device configuration and the double-junction-assisted increase

in effective triboelectric charge density. These results will pro-

vide useful morphological and architectural knowledge to enhance

and optimize the performance of wearable fabric-based TENGs.

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