Presented at the 5th International Conference on Energy Engineering and Smart Materials ICEESM 2020 Barcelona, Spain| April 15-17, 2020

1. Study of printed polymeric flexible energy
harvesting elements – impact of the electrode
materials and patterns
M Aleksandrova1, R Aepuru2, G Dobrikov1
1Technical university of Sofia, Department of Microelectronics, Sofia, Bulgaria
2University of Concepcion, Department of Materials Engineering,Concepcion, Chile
Corresponding author’s e-mail: m_aleksndrova@tu-sofia.bg
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5th International Conference on Energy Engineering and Smart Materials ICEESM 2020 Barcelona, Spain| April 15-17, 2020

2. Aim: To investigate different sets of piezoelectric energy harvesting (PEH) devices
with three different electrode materials and three different electrode topologies
(patterns) in terms of piezoelectric output voltage and long-term stability of the
produced signal.
Novelty: Study of the energy harvesting performance of piezoelectric device,
involving polymeric ink that was screen printed on gold, silver and aluminum with
square, meander and side-comb shapes patterns. By the authors‘ knowledge
similar problem has not been investigated yet.
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5th International Conference on Energy Engineering and Smart Materials ICEESM 2020 Barcelona, Spain| April 15-17, 2020

3. State-of-the-art
Application of the pressure/force/vibrational sensitive piezoelectric materials
energy harvesting or force detection – general term piezoelectric transducer.
Before – the sensor was few square
centimeter thick plate and cable
attachable to the electronics
Nowadays, it should be smaller
size, directly integrated into the
chip - MEMS 3
5th International Conference on Energy Engineering and Smart Materials ICEESM 2020 Barcelona, Spain| April 15-17, 2020

4. Source: https://www.dmg.msm.cam.ac.uk/research/nanogenerators
Piezoelectric based nanoelectromechanical systems (NEMS) are advanced technology for energy
harvesting devices, containing nanosized coatings, in cases when periodical mechanical activation
is available to stimulate charges generation. This technology has variety of applications.
Some of the most emerging applications using this effect are battery-less power supply for sensors
in the biomedicine, detecting human organs activity:
1. Heart beating rate; 2. Blood pressure change; 3. Breathing; 4. Arms or legs moving
For biomedical devices, lead-free piezoelectric materials have focused significant attention for
implants, where compatibility with the human tissue is crucial factor for selection of materials, but
this possibility is still under investigation (although there are reports for prototype of implantable
PEH for pacemakers, using normal motion of the heart-related blood vessels to generate power,
but they are not yet widely spread, due to reliability problems).
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5th International Conference on Energy Engineering and Smart Materials ICEESM 2020 Barcelona, Spain| April 15-17, 2020

5. 5
Currently, most of the real applications require wearable PEH.
APPLIED PHYSICS LETTERS 107, 202901 (2015)
Although the mechanical loads could be bending, stretching or twisting (or combination of
all), the goal is suitable PEH device mounting, so it will experience maximal load, but in the
same time it will experience dominantly (if possible) only one of the above loading types.
https://www.idtechex.com/ J. Mater. Chem. C, 2015,3, 11806-11814 http://www.somap.jku.at/ Nano Energy, Vol. 15, 2015, рр. 177-185
It was found that the bending is the most often met situation when human motions are in
question (press-release type, or compression-tension type).
This was our motivation to focus this study on flexible PEHs and their bending test
with loading vibration, causing compression-tension type of loading.
5th International Conference on Energy Engineering and Smart Materials ICEESM 2020 Barcelona, Spain| April 15-17, 2020

6. 6
Experimental section
5th International Conference on Energy Engineering and Smart Materials ICEESM 2020 Barcelona, Spain| April 15-17, 2020
a) bottom electrode patterns b) flexed PEN/Au c) completed structure
Photos of the prepared samples
• Polyethylene naphthalate (PEN) plastic substrates
125 μm.
• Screen printing of PVDF-TrFE polymeric ink with
mesh count of 180 n/cm and wire diameter of 30
µm was used and the deposition parameters were
squeegee speed of 200 mm/s and pressure of 3
bars. The film thickness was approximately 3 μm.
• Gold films was DC sputtered.
• Aluminium and silver electrode films were vacuum
thermally evaporated.
poly[(vinylidenefluoride-co-
trifluoroethylene] - P(VDF-TrFE)
• low Young modulus of 0.61 GPa,
• favourable for durability at bending
and twisting substrates

7. 7
Results
5th International Conference on Energy Engineering and Smart Materials ICEESM 2020 Barcelona, Spain| April 15-17, 2020
1 2 3
0
200
400
600
800
AlAuAg
piezoelectricvoltage,mV
types of metal electrodes
rectangular
meander
side comb
Comparison of the metals and their pattern
suitable for PVDF-TrFe piezoelectric flexible
elements at maximum mass load of 100 g
and 50 Hz in term of piezoelectric voltage.
Piezoelectric voltage generated from
PEN/Ag/PVDF-TrFe/Ag sample with
rectangular electrodes at mass load
of 80 g and frequency of 50 Hz.
As a general trend, the samples with side comb structures are characterized with
the weakest piezoelectric response, due to the smallest contact zones between
electrode and polymeric films, respectively the rectangular shape could give the
highest piezoelectric voltage due to the greatest contact area.

8. 8
0 200 400 600 800 100012001400
300
400
500
600
700
800
side comb
meander
rectangular
piezoelectricvoltage,mV
number of bends
5th International Conference on Energy Engineering and Smart Materials ICEESM 2020 Barcelona, Spain| April 15-17, 2020
0 200 400 600 800 100012001400
400
500
600
700
800
900
side comb
meander
rectangular
piezoelectricvoltage,mV
number of bends
0 200 400 600 800 100012001400
200
250
300
350
400
450
500
550
600
side comb
meander
rectangular
pipezoelectricvoltage,mV
number of bends
a) silver b) gold
c) aluminum
Stability of the piezoelectric voltage produced from PVDF-
TrFe samples with different metal electrodes and different
patterns of the electrodes at maximum mass load of 100 g
and low frequency of 20 Hz: a) silver; b) gold; c) aluminium.
• speed of degradation is strongly dependent on the
electrode shape.
• the side comb configuration exhibited the most
stable behavior (less than 2% degradation),
because the ink adhere mostly to the PEN
substrate.
• it was also found that there is relation with the
wetting ability of the electrode materials from the
polymeric ink during printing.

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5th International Conference on Energy Engineering and Smart Materials ICEESM 2020 Barcelona, Spain| April 15-17, 2020
a) b) c)
Microscopic images of PVDF-TrFe screen printed on
a) gold; b) aluminium and c) silver electrode surfaces.
• polymer printed on gold electrode is characterized with relatively low density coating,
• finer granular and more homogenous structure of the PVDF-TrFe with higher density
when printed on aluminium electrode
• polymer printed on silver exhibits the highest regularity and density. Although some
point defects could be noted, the film in between them is smooth.
Smooth, uniform surface is a precondition for stable and uniform contact at the interface
between the piezoelectric polymer and metal electrode with absence of strain effects
which tent to peal of the polymer and corrupt the electrical connection between the
coatings, thus resulting in piezoelectric voltage instability.

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5th International Conference on Energy Engineering and Smart Materials ICEESM 2020 Barcelona, Spain| April 15-17, 2020
Ag electrode Au electrode Al electrode
rectang. meand. s.comb rectang. meand. s.comb rectang. meand. s.comb
UPE, mV 916 840 446 800 768 362 528 400 258
ΔUPE @1500
bends, % 12.3 8.6 1.5 17.5 11.4 1.9 16.4 9.5 1.7
Polymer
microstru-
cture
Smooth, uniform and
dense coating
Relatively low
density coating
Fine granular, homogeneous
P, µW ~22.8 ~13 ~6.3
Comparison of the basic properties of piezoelectric harvester with three types
of metal electrodes and patterns.

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Conclusions:
5th International Conference on Energy Engineering and Smart Materials ICEESM 2020 Barcelona, Spain| April 15-17, 2020
• Flexible polymer based energy harvesting elements were produced by simple
processing and great compatibility with variety of substrates and electrode
materials.
• It was found that the silver electrodes are more favorable in terms of produced
piezoelectric voltage and quality of the printed polymer coating on them.
• It was demonstrated that the side comb shape electrodes provide the highest
stability of the piezoelectric voltage after great number of repeating bending
cycles, despite of the electrode material nature.
• As a general conclusion, the meander electrodes could be a balanced
compromise between electrical performance and mechanical stability.
• Another key outcome of the experimental work is the obtaining of a well
controllable screen printed coating on surfaces with different wettability with
piezoelectric polymer ink, based on P(VDF-TrFE) material.
• Future work will be focused on experimental study of the frequency and
temperature dependences of the dielectric permittivity and loss factor of flexible
energy harvesting with screen printed PVDF-TrFe films with the proposed
electrodes topologies.

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THANK YOU FOR YOUR ATTENTION!
Acknowledgements: The authors acknowledge the funding support from BNSF, grant DH 07/13.
5th International Conference on Energy Engineering and Smart Materials ICEESM 2020 Barcelona, Spain| April 15-17, 2020