Q. DAI et al.: A SCREEN-PRINTED PIEZOELECTRIC ENERGY HARVESTER USING ZnO TETRAPOD ARRAYS
231–234
A SCREEN-PRINTED PIEZOELECTRIC ENERGY HARVESTER
USING ZnO TETRAPOD ARRAYS
SITOTISK PIEZOELEKTRI^NEGA ZBIRALCA ENERGIJE
Z UPORABO ZnO TETRAPODNIH MATRIC
Quili Dai1,2, Peng Pan1,2, Ruifeng Zhang1,2, Jun Liu2, Zhengcun Yang2, Jun Wei2,
Qiping Yuan1,2
1Tianjin University of Technology, Tianjin Key Laboratory of Film Electronic and Communicate Devices, School of Electrical and Electronic
Engineering, Tianjin 300384, China
2Tianjin University of Technology, Advanced Materials and Printed Electronics Center, School of Electrical and Electronic Engineering,
Tianjin 300384, China
13072219279@163.com
Prejem rokopisa – received: 2017-09-25; sprejem za objavo – accepted for publication: 2017-10-20
doi:10.17222/mit.2017.157
In this work, for the first time, we combine electronic printing technology, electrostatic spraying technology and the new 3D
structure of ZnO. The new structure was prepared with a simple, low-cost and massive method that was not successfully applied
before. The ZnO tetrapods/PET composite device exhibits an output open-circuit voltage of ~20 V and a short-circuit current of
~300nA under repeated hand pressing. It is demonstrated that the output power from the PENG can directly drive the
light-emitting diodes (LEDs) and charge a capacitor. But a typical flexible polymer produces an output voltage of 3.3 V and
cannot power light-emitting diodes.
Keywords: ZnO tetrapods, wearable electronics, nanogenerator, screen-printed
V tem ~lanku avtorji prvi~ opisujejo kombinacijo tehnologije elektronskega tiska, tehnologije elektrostati~nega napr{evanja in
nove 3D-strukture ZnO. Novo strukturo so pripravili z enostavno, ceneno in produktivno metodo, ki do sedaj {e ni bila razvita.
Kompozitna naprava sestavljena iz ZnO tetrapodov in polietilen tereftalata (PET), ima v odprtem tokokrogu napetost ~ 20 V in
kratkosti~ni tok ~ 300 nA pod vplivom ponavljajo~ega ro~nega stiskanja. Avtorji so v raziskavi dokazali, da je izhodna mo~
piezoelektri~nega nanogeneratorja (PENG) dovolj velika, da lahko neposredno poganja svetlobne diode (LEDs; angl.:
light-emitting diodes) in polni kondenzator. Toda tipi~ni upogljivi (fleksibilni, tisti ki se prilagajajo telesu) polimerni proizvodi
imajo izhodno napetost 3,3 V in ne morejo proizvajati svetlobe z LED-icami.
Klju~ne besede: ZnO tetrapodi, nosljiva elektronika, nanogenerator, sitotisk
1 INTRODUCTION
In various renewable and sustainable energy environ-
ments, mechanical energy is the largest widely distri-
buted resource1,2 with a variety of energy types and
scales, such as pressure, sound, rolling tires, vibration,
and tides. In order to solve the problem of increasing
energy crisis and realize the low-energy-consumption
electronics of power supply, various methods have been
developed to convert mechanical energy into electricity,
including the piezoelectric effect, electrostatic3,4 etc. In
practice, each kind of generator has its own shortcoming,
i.e., it can simultaneously mass produce, and popularize
multi-type generator5 to improve energy production har-
vester. In the previous work, the simulation analysis of
the coupling between the piezoelectric friction and elec-
tronics have been promoting the output performance of a
piezoelectric–triboelectric hybrid nanogenerator can be
achieved through proper structural design and the direc-
tion of the polarization enhancement.6
In this work we fabricated a novel structured piezo-
electric nanogenerator (PENG) based on polyethylene
terephthalate (PET) and polydimethysiloxane (PDMS)
film that was printing carbon paste with screen-printed
and electrostatic spraying ZnO tetrapods.7,8 In the
demonstration, the ZnO tetrapods four of the three legs
are arranged on the substrate below, and look like a tetra-
hedron. These ZnO tetrapods were synthesized through a
simple, low-cost, low-temperature hydrothermal me-
thod,9,10 which can facilitate large-scale production and
preparation. The electrical output of a PENG with
surface modification of the ZnO tetrapods could reach
20 V at low frequency, about 2.3 times higher than that
without any ZnO materials. This clearly suggests that
this kind of surface modification can dramatically
enhance the electrical output of the PENG, providing a
unique microstructured material for the PENG.
2 EXPERIMENTAL PART
2.1 Materials
The graphite used in the experiments was purchased
from Sigma-Aldrich. Polyethylene terephthalate (PET)
and polydimethysiloxane (PDMS) film, 99 % pure Zn
powder, ethanol and acetone were obtained from Sigma-
Aldrich.
Materiali in tehnologije / Materials and technology 52 (2018) 2, 231–234 231
UDK 621.38:620.3:681.6-33 ISSN 1580-2949
Original scientific article/Izvirni znanstveni ~lanek MTAEC9, 52(2)231(2018)
2.2 Preparation of ZnO nanotetrapods
ZnO nanotetrapods were synthesized with 99 % pure
Zn powder by a thermal evaporation and oxidation
method in air. An induction-heating device with a maxi-
mum output power of 60 kW and a constant frequency of
60 kHz was used as a heating source. The induction coil
made of a copper tube was processed into a shape of
planar polyring. First, the Zn powder was paved evenly
onto a sheet of graphite paper. The graphite paper was
parallel to the induction coil and the distance between
them kept at 30 mm. In order to investigate the effect of
the output power on the morphologies of the ZnO nano-
tetrapods11,12 the applied value of output power varied
from 20 kW to 40 kW. After a few seconds from starting
the induction-heating device, white cotton-like product
filled the space between the induction coil and the
graphite paper.
2.3 Fabrication of piezoelectric nanogenerator films
The white products of ZnO nanotetrapods were
obtained in the crucibles and were collected for the next
step to use. Before the in printing carbon paste, the
substrates were cleaned ultrasonically in acetone, ethanol
and deionized water. Then the substrates were dried at
60 °C for 0.5 h and printed with carbon paste using
screen-printing technology. Finally, the ZnO tetrapods on
the basis of printing carbon paste by electrostatic
spraying and oven for half an hour at 110 °C in the air at
atmospheric pressure.
The schematic diagram of the PENG manufacturing
process is introduced in Figure 1a. The PENG were
manufactured by covering the top PDMS with graphite
as electrodes and bottom surfaces of graphite paste on a
polyethylene terephthalate (PET) substrate. The particu-
lar information about the manufacturing process is
described in the Experimental details. The dimension of
the fabricated PENG is the rectangular area of mm2 show
in Figure 1b.
3 RESULTS AND DISCUSSION
Figure 2 shows typical scanning electron microscopy
(SEM) images (Figure 2a and 2b) of the as-synthesized
Q. DAI et al.: A SCREEN-PRINTED PIEZOELECTRIC ENERGY HARVESTER USING ZnO TETRAPOD ARRAYS
232 Materiali in tehnologije / Materials and technology 52 (2018) 2, 231–234
Figure 2: Representative SEM images shown up view: a) and b) of
ZnO nanotetrapods, c) Rietveld-refinement analysis of XRD spectra of
ZnO nanotetrapods
Figure 1: a) Schematic diagrams of the PENG fabricating process,
b) photograph of the ZnO-PET composite film contact by wires
products prepared under different magnifications. The
SEM image shows that the products are composed of
four-dollar ZnO crystals and extends four legs from the
center. Figure 2c is the XRD mode of ZnO, while the
sharp diffraction peak indicates good crystal quality. All
the 12 diffraction peaks can be associated with ZnO
crystals (JCPDS 36-1451) of hexagonal fiber structure,
indicating that ZnO crystals have a high purity.13
The pattern is a vertical contact-separation mode of
PENG. The detailed working principle is shown in Fig-
ure 3a. When the PENG is pressed, the two friction
materials contact. According to the previous works, due
to the different electron-attracting ability, is transported
from one material to another electrons14 so there will be
a net negative charge of the surface layer and attract
electron ability and net positive charge Figure 3b. Two
tribo-materials, independent of the interface area of the
tribo-materials earlier separation, this will lead to the
interface area being saved, so the electronic connection
induction electrode will drive the flow from one side to
to another (creating a current cycle, Figure 3c). In the
process, the electron lasts until the PENG is fully re-
leased, shown in Figure 3d. At this point, both the
induces the potential difference and the transfer charge
of the maximum.15,16 As these two tribo-materials disso-
ciate,17,18 the potential differences will decrease and the
electrons will also appear and Returns even fade away
(Figure 3a). Therefore, the whole process will produces
an optional current pulse output. When two thin films are
exposed and separated, the replacement potential will
drive the electrons in the external load to move back and
forth. But typical flexible polymer produces an output
voltage of 3.3 V and cannot power light-emitting diodes.
Open-circuit voltage (Voc) and short-circuit current
(Isc) are measured to characterize the PENG electric
performance when it is coated with graphite.19 With a
repeating finger imparting (pressure amplitude ~8.43
kPa, online supplementary data) the Voc is presented in
Figure 4a. Furthermore, the AC output could be trans-
ferred to the pulse output in the same direction simply by
introducing a full-wave rectifying bridge (Figure 4d). At
an applied pressure of 8.43 kPa, the PENG is able to
produce a Voc up to 20 V and the short-circuit current
Isc is 300 nA. When the force decreases, (pressure am-
plitude ~3.45 kPa) the output voltage decreases as the
Voc is 6 V (Figure 4b). This is attributed to the in-
creased contact area between the electrode and the
PDMS with a larger applied pressure amplitude. The
PDMS shows an elastic property; the larger force PDMS
can fill more vacant space, thus leading to a larger
contact area. As a result, the electric output voltage and
current increase until all of the vacant spacing is
completely filled by the PDMS,20 reaching an enhanced
output. Different values of the resistors are connected as
a PENG to further investigate the effective electric power
of the PENG. As demonstrated in Figure 4c, the in-
stantaneous current drops with increasing load resistance
due to ohmic losses, while the voltage builds up.21,22 Con-
sequently, the instantaneous power output (W = I2peak R)
reached the maximum at a load resistance of 0.6 M. At
a contacting force of 8.43 kPa, an power output of
0.4 μW was achieved (Figure 4d).To confirm the energy
storage application of the PENG, a capacitor was
connected to the NG using a full-wave bridge rectifying
circuit.23
The electric power generated by the PENG is directly
used for the opening of commercial LEDs lights.24 In the
process of finger tapping, 9 commercial LEDS are driven
Q. DAI et al.: A SCREEN-PRINTED PIEZOELECTRIC ENERGY HARVESTER USING ZnO TETRAPOD ARRAYS
Materiali in tehnologije / Materials and technology 52 (2018) 2, 231–234 233
Figure 4: a) and b) under different finger pressures rectified output
voltage of the PNG, c) fitted curve of the current and voltage output
on different external load resistance, d) dependence of the power
output on the different external load resistance, e) equivalent bridge
rectifier circuit diagram for the DC voltage measurement, capacitor
charging and LED lighting performance, f) the LEDs were driven
successively by output generated from hand pressing
Figure 3: Working mechanism of the sandwich-shape PNG. Sche-
matic illustration of the charge-generating process of the PNG. Pushed
by the external force from the linear motor, the device will be
switching back and forth between the separated state and the contacted
state, and there will be an alternating flow of electrons in the external
circuit driven by the induced priboelectric potential. The electric
charges move for neutralization after the separation, forming a cycle.
by the resulting output voltage (Figure 4f), which does
not require external energy-storage devices (inset of Fig-
ure 4e).
4 CONCLUSIONS
In summary, we have successfully provided a simple,
low-cost and massive production method to fabricate
ZnO tetrapods electrets film based on nanogenerator,
e.g., PENG. The mechanical energy-harvesting ability of
the PENG is demonstrated by powering 9 light-emitting
diodes (LEDs) by a simple finger touch. For the tradi-
tional energy-harvester flexible polymer produces an
output voltage of 3.3 V and cannot power light-emitting
diodes (LEDs). This is a simple and cost-effective me-
thod to realize the output enhancement of piezoelectric
PENG. High output enables the energy harvesters to be
used as power sources for light-emitting diodes or
rechargeable capacitors, showing great potential in the
field of self-powered systems or sensor networks.
Acknowledgments
This work was financially supported by The
Recruitment Program of Global Experts and Advanced
Materials and Printed Electronics Center.
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Q. DAI et al.: A SCREEN-PRINTED PIEZOELECTRIC ENERGY HARVESTER USING ZnO TETRAPOD ARRAYS
234 Materiali in tehnologije / Materials and technology 52 (2018) 2, 231–234