Piezoelectric Nanogenerator Based on Lead-Free Flexible PVDF-Barium Titanate Composite Films for Driving Low Power Electronics

: Self-powered sensor development is moving towards miniaturization and requires a suitable power source for its operation. The piezoelectric nanogenerator (PENG) is a potential candidate to act as a partial solution to suppress the burgeoning energy demand. The present work is focused on the development of the PENG based on ﬂexible polymer-ceramic composite ﬁlms. The X-ray spectra suggest that the BTO particles have tetragonal symmetry and the PVDF-BTO composite ﬁlms (CF) have a mixed phase. The dielectric constant increases with the introduction of the particles in the PVDF polymer and the loss of the CF is much less for all compositions. The BTO particles have a wide structural diversity and are lead-free, which can be further employed to make a CF. An attempt was made to design a robust, scalable, and cost-effective piezoelectric nanogenerator based on the PVDF-BTO CFs. The solvent casting route was a facile approach, with respect to spin coating, electrospinning, or sonication routes. The introduction of the BTO particles into PVDF enhanced the dielectric constant and polarization of the composite ﬁlm. Furthermore, the single-layered device output could be increased by strategies such as internal polarization ampliﬁcation, which was conﬁrmed with the help of the polarization-electric ﬁeld loop of the PVDF-BTO composite ﬁlm. The piezoelectric nanogenerator with 10 wt% BTO-PVDF CF gives a high electrical output of voltage 7.2 V, current 38 nA, and power density of 0.8 µ W/cm 2 at 100 M Ω . Finally, the energy harvesting using the fabricated PENG is done by various actives like coin dropping, under air blowing, and ﬁnger tapping. Finally, low-power electronics such as calculator is successfully powered by charging a 10 µ F capacitor using the PENG device. complicated spin dielectric The Polarization-electric ﬁeld loop polarization of PVDF. the single-layered device by such internal polarization ampliﬁcation. This work paves the way to fabricate new piezoelectric material for energy


Introduction
In the present era, the development of a sustainable and flexible energy harvester that harvests energy from listed mechanical sources to power electronics and nanosystems is attaining huge attention [1,2]. Nanogenerators provide a pathway towards sustainable power sources due to their superior characteristics of easy, less cost fabrication, mass production, improved energy conversion efficiency [3,4]. Currently, the quest is to develop flexible nanogenerators working on principles of piezoelectricity [5] and triboelectricity [6]. Nanogenerators based on the piezoelectric principle have gained immense attention due to many advantages such as wide piezoelectric materials selection, easy fabrication, and quick response [7,8]. The various structure and shapes of the flexible piezoelectric nanogenerator can be achieved by using several polymers like PVDF, PVDF-copolymer [9], PDMS [10], Nylon [11], and polyamide [12]. Among these, PVDF and its copolymers are chosen for

Synthesis of BaTiO 3 Particles
The BTO particles were synthesized by mixing the various precursors and heat treatment at high temperature. The high purity barium carbonate and titanium oxide were procured from Loba Chemie, Mumbai, India. The stoichiometric proportion of the powders were carefully measured using a digital weighing balance. The powders were transferred to an agate mortar and mixed for 2 h in a methanol medium. The homogeneously mixed powders were put into an alumina boat and calcined inside a box furnace at 1200 • C for 4 h. Further, the lump was ground into fine particles utilizing an agate mortar and pestle.

Synthesis of PVDF-BaTiO 3 Composite Film and PENG Device
The composite film (CF) of the PVDF-BTO was prepared by a cost-effective solvent casting method. For this, a solvent of N-Methyl-2-Pyrrolidone (NMP) was procured from Sisco Research Ltd., Mumbai, India. The PVDF pellets were procured from Sigma Aldrich, St. Louis, MO, USA. The PVDF pellets were measured in proper ratio and put into the NMP solvent at 60 • C upon a magnetic stirrer with a magnetic bead inside it. The clear transparent solution was obtained after 1 h, and the various wt% of the BTO particles were put into the solution. Dispersions with different concentrations of BTO (1 wt%, 5 wt%, 7 wt%, 10 wt%) were prepared. Further, it was allowed to mix for 1 h at room temperature until a homogenous mixture was achieved. Then the PVDF-BTO solution was poured onto a glass Petri plate and left inside an electric oven at 70 • C for two hours. After curing, a free-standing flexible PVDF-BTO CF was obtained.
For the PENG device fabrication, the film was cut into dimensions of 1.5 cm × 1.5 cm, and the gold coating was done to act as an electrode. The electrode area was kept as 1 cm × 1 cm. Further, to measure the system's energy output, thin copper tape was attached to the opposite side of the device. It was then transferred to antistatic tape to neglect any of the electrostatic charges present in the environment. Then the entire device was encapsulated using a PDMS layer. The PENG devices were poled at 1 kV for 30 min at RT to align dipoles.

Experimental Techniques
The structural analysis of the BTO particles and PVDF-BTO CFs were performed using a powder X-ray diffraction (PANalytical Empyrean, Almelo, The Netherlands, Cu-Kα radiation) under a scanning step size of 3 • /min. The surface morphology was taken using a Hitachi S-4800 scanning electron microscope fitted with an EDS detector. The CF was cut into small pieces, and the electrode was done with gold sputtering onto opposite sides for electrical characterization at room temperature. The dielectric measurement was taken using an N4L PSM LCR meter. The periodic contact-separation of the device was performed by a linear motor (LinMot Inc., Lake Geneva, WI, USA). An electrometer 6514 (Keithley, Solon, OH, USA) was used to measured voltage and current from the piezoelectric device.

Results and Discussion
The systematic synthesis route is the possible way to properly obtain a high crystalline material and with superior properties. In Figure 1a, the mixing of the high purity barium carbonate and titanium oxide is mixed using a mortar and pestle in the presence of the methanol for 4 h and then transferred into an alumina crucible. The mixture is calcined at 1200 • C for 4 h. The morphological properties, such as particle size and shape of prepared BTO particles were analyzed from the captured SEM image, as shown in Figure 1a. The SEM image reveals the polyhedron shape of particles with a very smooth surface and edges. The particle size histogram with a Gaussian peak fitted curve is shown in Figure S1a. It depicts the presence of particles having a size distribution in the range of 200 to 1300 nm. The average particle size was about 460 nm, which was calibrated from the Gaussian peak fitting of the particle size distribution histogram. Figure 1b shows the formation of the PVDF-BTO CF. In this, the PVDF pellets are dissolved in the NMP solvent and heated at Crystals 2021, 11, 85 4 of 10 60 • C for 1 h using a magnetic stirring. Then the BTO particles are added to the transparent solution and the temperature is reduced to room temperature with continuous mixing giving rise to a PVDF-BTO homogenous solution. It is then poured onto a glass Petri dish and left for curing. The contact angle measurement of the PVDF-BTO films shows an angle greater than 100 degrees, which suggests the higher hydrophobic nature of the films. Figure 1c shows the XRD pattern of the BTO particles at room temperature. The peaks are well-matched with reported JCPDS data: 01-075-0583. The POWD MULT software was used to derive the lattice parameters following a least-square refinement rule. The values of a: 3.988 ( 1, 11, x FOR PEER REVIEW 4 of 10 surface and edges. The particle size histogram with a Gaussian peak fitted curve is shown in Figure S1a. It depicts the presence of particles having a size distribution in the range of 200 to 1300 nm. The average particle size was about 460 nm, which was calibrated from the Gaussian peak fitting of the particle size distribution histogram. Figure 1b shows the formation of the PVDF-BTO CF. In this, the PVDF pellets are dissolved in the NMP solvent and heated at 60 °C for 1 hour using a magnetic stirring. Then the BTO particles are added to the transparent solution and the temperature is reduced to room temperature with continuous mixing giving rise to a PVDF-BTO homogenous solution. It is then poured onto a glass Petri dish and left for curing. The contact angle measurement of the PVDF-BTO films shows an angle greater than 100 degrees, which suggests the higher hydrophobic nature of the films. Figure 1c shows the XRD pattern of the BTO particles at room temperature. The peaks are well-matched with reported JCPDS data: 01-075-0583. The POWD MULT software was used to derive the lattice parameters following a least-square refinement rule. The values of a: 3.988 ( Ǻ ); c: 3.979 (Ǻ); volume: 64.2 (Ǻ 3 ). The XRD peaks of the polymer ceramic CFs showed the presence of both PVDF and BTO phases. Various symbols were used to represent the PVDF phase and the perovskite phase of BTO. It was depicted that a higher concentration of 10 wt% into the PVDF leads to an increase in the BTO phase and a reduction in the PVDF phase intensity. It can be also noticed that the phase of the BTO has not been altered as it gets dissolved in PVDF, which can be confirmed as there is no peak shifting occurred in the polymer-ceramic CF.  surface and edges. The particle size histogram with a Gaussian peak fitted curve is shown in Figure S1a. It depicts the presence of particles having a size distribution in the range of 200 to 1300 nm. The average particle size was about 460 nm, which was calibrated from the Gaussian peak fitting of the particle size distribution histogram. Figure 1b shows the formation of the PVDF-BTO CF. In this, the PVDF pellets are dissolved in the NMP solvent and heated at 60 °C for 1 hour using a magnetic stirring. Then the BTO particles are added to the transparent solution and the temperature is reduced to room temperature with continuous mixing giving rise to a PVDF-BTO homogenous solution. It is then poured onto a glass Petri dish and left for curing. The contact angle measurement of the PVDF-BTO films shows an angle greater than 100 degrees, which suggests the higher hydrophobic nature of the films. Figure 1c shows the XRD pattern of the BTO particles at room temperature. The peaks are well-matched with reported JCPDS data: 01-075-0583. The POWD MULT software was used to derive the lattice parameters following a least-square refinement rule. The values of a: 3.988 ( Ǻ ); c: 3.979 (Ǻ); volume: 64.2 (Ǻ 3 ). The XRD peaks of the polymer ceramic CFs showed the presence of both PVDF and BTO phases. Various symbols were used to represent the PVDF phase and the perovskite phase of BTO. It was depicted that a higher concentration of 10 wt% into the PVDF leads to an increase in the BTO phase and a reduction in the PVDF phase intensity. It can be also noticed that the phase of the BTO has not been altered as it gets dissolved in PVDF, which can be confirmed as there is no peak shifting occurred in the polymer-ceramic CF.  surface and edges. The particle size histogram with a Gaussian peak fitted curve is shown in Figure S1a. It depicts the presence of particles having a size distribution in the range of 200 to 1300 nm. The average particle size was about 460 nm, which was calibrated from the Gaussian peak fitting of the particle size distribution histogram. Figure 1b shows the formation of the PVDF-BTO CF. In this, the PVDF pellets are dissolved in the NMP solvent and heated at 60 °C for 1 hour using a magnetic stirring. Then the BTO particles are added to the transparent solution and the temperature is reduced to room temperature with continuous mixing giving rise to a PVDF-BTO homogenous solution. It is then poured onto a glass Petri dish and left for curing. The contact angle measurement of the PVDF-BTO films shows an angle greater than 100 degrees, which suggests the higher hydrophobic nature of the films. Figure 1c shows the XRD pattern of the BTO particles at room temperature. The peaks are well-matched with reported JCPDS data: 01-075-0583. The POWD MULT software was used to derive the lattice parameters following a least-square refinement rule. The values of a: 3.988 ( Ǻ ); c: 3.979 (Ǻ); volume: 64.2 (Ǻ 3 ). The XRD peaks of the polymer ceramic CFs showed the presence of both PVDF and BTO phases. Various symbols were used to represent the PVDF phase and the perovskite phase of BTO. It was depicted that a higher concentration of 10 wt% into the PVDF leads to an increase in the BTO phase and a reduction in the PVDF phase intensity. It can be also noticed that the phase of the BTO has not been altered as it gets dissolved in PVDF, which can be confirmed as there is no peak shifting occurred in the polymer-ceramic CF.  Figure 2a shows the surface morphology of the CF. It shows that the BTO concentration increases in the PVDF and there is no clustering of the particles. The 10 wt% BTO-3 ). The XRD peaks of the polymer ceramic CFs showed the presence of both PVDF and BTO phases. Various symbols were used to represent the PVDF phase and the perovskite phase of BTO. It was depicted that a higher concentration of 10 wt% into the PVDF leads to an increase in the BTO phase and a reduction in the PVDF phase intensity. It can be also noticed that the phase of the BTO has not been altered as it gets dissolved in PVDF, which can be confirmed as there is no peak shifting occurred in the polymer-ceramic CF.
1a. The SEM image reveals the polyhedron shape of particles with a very smooth surface and edges. The particle size histogram with a Gaussian peak fitted curve is shown in Figure S1a. It depicts the presence of particles having a size distribution in the range of 200 to 1300 nm. The average particle size was about 460 nm, which was calibrated from the Gaussian peak fitting of the particle size distribution histogram. Figure 1b shows the formation of the PVDF-BTO CF. In this, the PVDF pellets are dissolved in the NMP solvent and heated at 60 °C for 1 h using a magnetic stirring. Then the BTO particles are added to the transparent solution and the temperature is reduced to room temperature with continuous mixing giving rise to a PVDF-BTO homogenous solution. It is then poured onto a glass Petri dish and left for curing. The contact angle measurement of the PVDF-BTO films shows an angle greater than 100 degrees, which suggests the higher hydrophobic nature of the films. Figure 1c shows the XRD pattern of the BTO particles at room temperature. The peaks are well-matched with reported JCPDS data: 01-075-0583. The POWD MULT software was used to derive the lattice parameters following a least-square refinement rule. The values of a: 3.988 (Ǻ); c: 3.979 (Ǻ); volume: 64.2 (Ǻ 3 ). The XRD peaks of the polymer ceramic CFs showed the presence of both PVDF and BTO phases. Various symbols were used to represent the PVDF phase and the perovskite phase of BTO. It was depicted that a higher concentration of 10 wt% into the PVDF leads to an increase in the BTO phase and a reduction in the PVDF phase intensity. It can be also noticed that the phase of the BTO has not been altered as it gets dissolved in PVDF, which can be confirmed as there is no peak shifting occurred in the polymer-ceramic CF.   Figure 2a shows the surface morphology of the CF. It shows that the BTO concentration increases in the PVDF and there is no clustering of the particles. The 10 wt% BTO-PVDF CF show more compactness as compared to other CF. The EDS spectra of the 10 wt% BTO-PVDF shows that all the elements are present without any trace of impurity. Figure 2b shows the frequency-dependent dielectric constant at room temperature. It shows that the dielectric contact rises as the BTO particles in the PVDF increases. The pure PVDF shows Crystals 2021, 11, 85 5 of 10 23 dielectric constant values at 1 kHz while the 10 wt% BTO-PVDF CF shows 47 at 1 kHz, suggesting that there is a rise in connectivity between the particles as the BTO content rises to improve the dipole-dipole interaction [33]. The reason behind the increase in the dielectric constant in low frequency is mainly due to the effect of various polarizations, and with a rise in frequency, the polarization activity fades, leading to constant or reduced dielectric constant magnitude. Figure 2c shows the dielectric loss versus frequency at room temperature for various CF. The interfacial polarization could lead to a rise in the loss factor in the low-frequency region. The heterogeneity in the CF, with a rise in the BTO content in the PVDF, is also responsible for increasing the loss factor as the BTO. Another possible cause may be from the air voids ionization, which creates plasma as an electric field is applied to the CF. Figure 2d shows the digital image of the fabricated piezoelectric device, which is flexible and bendable. The ferroelectric polarization of the pure PVDF and PVDF-BTO (10 wt%) is compared in Figure S1b. The remnant polarization of the PVDF is 0.52 µC/cm 2, whereas for the PVDF-BTO CF it is 0.66 µC/cm 2 . It demonstrates that as the BTO content increases in the PVDF, the dielectric constant and ferroelectric polarization are both improved in the material. It is also noted that the relation below links the dielectric property to the piezoelectric voltage co-efficient: g ij = d ij /(ε 0 ε r ). Therefore, as the dielectric constant increases, the piezoelectric output response should also rise.
wt% BTO-PVDF shows that all the elements are present without any trace of impurity. Figure 2b shows the frequency-dependent dielectric constant at room temperature. It shows that the dielectric contact rises as the BTO particles in the PVDF increases. The pure PVDF shows 23 dielectric constant values at 1 kHz while the 10 wt% BTO-PVDF CF shows 47 at 1 kHz, suggesting that there is a rise in connectivity between the particles as the BTO content rises to improve the dipole-dipole interaction [33]. The reason behind the increase in the dielectric constant in low frequency is mainly due to the effect of various polarizations, and with a rise in frequency, the polarization activity fades, leading to constant or reduced dielectric constant magnitude. Figure 2c shows the dielectric loss versus frequency at room temperature for various CF. The interfacial polarization could lead to a rise in the loss factor in the low-frequency region. The heterogeneity in the CF, with a rise in the BTO content in the PVDF, is also responsible for increasing the loss factor as the BTO. Another possible cause may be from the air voids ionization, which creates plasma as an electric field is applied to the CF. Figure 2d shows the digital image of the fabricated piezoelectric device, which is flexible and bendable. The ferroelectric polarization of the pure PVDF and PVDF-BTO (10 wt%) is compared in Figure S1b. The remnant polarization of the PVDF is 0.52 μC/cm 2, whereas for the PVDF-BTO CF it is 0.66 μC/cm 2 . It demonstrates that as the BTO content increases in the PVDF, the dielectric constant and ferroelectric polarization are both improved in the material. It is also noted that the relation below links the dielectric property to the piezoelectric voltage co-efficient: gij = dij/(ε0εr). Therefore, as the dielectric constant increases, the piezoelectric output response should also rise.   Figure 3a shows the working mechanism of the piezoelectric nanogenerator device. In general, if a mechanical force is applied to a PENG device, there is the generation of positive and negative piezoelectric potential in the materials leading to an electrical output at both ends of electrodes. It is seen as the pressure is acted upon by the piezoelectric nanogenerator, the electrons flow from one end to the other, leading to the flow of current Crystals 2021, 11, 85 6 of 10 through an external load. As the force is removed, the stored electrons move through the external circuit in a reverse manner creating a negative voltage. This repeated process leads to the generation of the output of PENG. Figure 3b shows the representation of the dipoles; as we apply a voltage of 1 kV across the piezoelectric CF the dipoles are aligned, which is required to achieve higher piezoelectric output. Figure 3c shows the layer by layer arrangement of the PENG device; it has several layers sandwiched into one structure. The antistatic tape is used to remove any stray charges in the air atmosphere while the PDMS encapsulation act as a packing layer. Figure 3d,e shows the voltage and current output of the various PENG devices. The 1 wt% BTO in PVDF (PNG1), 5 wt% BTO in PVDF (PNG5), 7 wt% BTO in PVDF (PNG7), and 10 wt% BTO in PVDF (PNG10) are the abbreviated names of the fabricated PENG devices. It is seen that the PNG20 shows a higher output of voltage 7.2 V/current 38 nA. Figure 3f presents the switching polarity test confirming that the generated outputs are due solely to the piezoelectric effect. It is to note that no change in phase in the peak pattern, indicative of a true piezoelectric response. Figure 3a shows the working mechanism of the piezoelectric nanogenerator device. In general, if a mechanical force is applied to a PENG device, there is the generation of positive and negative piezoelectric potential in the materials leading to an electrical output at both ends of electrodes. It is seen as the pressure is acted upon by the piezoelectric nanogenerator, the electrons flow from one end to the other, leading to the flow of current through an external load. As the force is removed, the stored electrons move through the external circuit in a reverse manner creating a negative voltage. This repeated process leads to the generation of the output of PENG. Figure 3b shows the representation of the dipoles; as we apply a voltage of 1 kV across the piezoelectric CF the dipoles are aligned, which is required to achieve higher piezoelectric output. Figure 3c shows the layer by layer arrangement of the PENG device; it has several layers sandwiched into one structure. The antistatic tape is used to remove any stray charges in the air atmosphere while the PDMS encapsulation act as a packing layer. Figure 3d,e shows the voltage and current output of the various PENG devices. The 1 wt% BTO in PVDF (PNG1), 5 wt% BTO in PVDF (PNG5), 7 wt% BTO in PVDF (PNG7), and 10 wt% BTO in PVDF (PNG10) are the abbreviated names of the fabricated PENG devices. It is seen that the PNG20 shows a higher output of voltage 7.2 V/current 38 nA. Figure 3f presents the switching polarity test confirming that the generated outputs are due solely to the piezoelectric effect. It is to note that no change in phase in the peak pattern, indicative of a true piezoelectric response.   Figure 4a,b shows the current and voltage of the PNG10 device at various accelerations/frequencies. It is seen that at higher acceleration/frequencies, the output of the device is not uniform as the device may be depolarized with higher acceleration. Figure 4c shows the loading matching analysis of the PNG10 device. The power density (P = V 2 /R) of the PNG10 device under optimized conditions is determined by varying the load matching R from kΩ to GΩ and measuring the corresponding voltage. It was observed that a power density of 0.8 µW/cm 2 at 100 MΩ was achieved by the PNG10 device. Figure 4d shows the charging of the various capacitor with different capacitance. Figure 4e shows the charging and discharging curve of the 4.7 µF capacitor several times, which shed light upon the fact that the output generated by the PNG10 device is stable for a long time. Figure 4f shows the stored charge in each capacitor that was calculated using the formula Q = CV. Figure 4 a,b shows the current and voltage of the PNG10 device at various accelera tions/frequencies. It is seen that at higher acceleration/frequencies, the output of the de vice is not uniform as the device may be depolarized with higher acceleration. Figure 4c shows the loading matching analysis of the PNG10 device. The power density (P = V 2 /R of the PNG10 device under optimized conditions is determined by varying the load matching R from kΩ to GΩ and measuring the corresponding voltage. It was observed that a power density of 0.8 μW/cm 2 at 100 MΩ was achieved by the PNG10 device. Figure  4d shows the charging of the various capacitor with different capacitance. Figure 4e show the charging and discharging curve of the 4.7 μF capacitor several times, which shed ligh upon the fact that the output generated by the PNG10 device is stable for a long time Figure 4f shows the stored charge in each capacitor that was calculated using the formula Q = CV. The real-time energy harvesting from the PNG10 was carried out using several activ ities. Figure 5 shows the output voltage when a coin was dropped upon the device PNG10 it could sense the impact from the dropping of the coin. In Figure 5b, the PNG10 device was connected to the fan, and when the fan was turned on at its highest speed, the device could produce 6.9 V. Figure 5c,d demonstrates the biomechanical energy harvesting from the PNG10 device was tested by simple finger tapping and the voltage of 1.4 V and curren of 24 nA. To demonstrate, the powering of the calculator in Figure 5e,f, two PNG10 de vices were connected in parallel to increase the current produced from the device, and this was utilized directly to charge a 10 μF capacitor. The AC signal produced by the two PNG10 devices is converted to DC via a bridge rectifier circuit. When the switch was ON the calculator began to work and the capacitor was discharged. Figure 5f shows the digita image of the demonstration of the powering of the calculator. Hence the fabrication of the PVDF-BTO CFs based flexible nanogenerator paves the way towards a sustainable powe source and a promising entrant for designing self-power applications. Figure S2a show the result of the manual bending test: as the device is flexible, it could easily bend and produce an electrical output. Figure S2b,c show the electrical response of the device while performing an exercise like a basic squat exercise. The device generated an electrical volt age of 6 V and a current of 19 nA, demonstrating that the presented PENG device can be used for counting the number of times the exercise was performed. The real-time energy harvesting from the PNG10 was carried out using several activities. Figure 5 shows the output voltage when a coin was dropped upon the device PNG10 it could sense the impact from the dropping of the coin. In Figure 5b, the PNG10 device was connected to the fan, and when the fan was turned on at its highest speed, the device could produce 6.9 V. Figure 5c,d demonstrates the biomechanical energy harvesting from the PNG10 device was tested by simple finger tapping and the voltage of 1.4 V and current of 24 nA. To demonstrate, the powering of the calculator in Figure 5e,f, two PNG10 devices were connected in parallel to increase the current produced from the device, and this was utilized directly to charge a 10 µF capacitor. The AC signal produced by the two PNG10 devices is converted to DC via a bridge rectifier circuit. When the switch was ON, the calculator began to work and the capacitor was discharged. Figure 5f shows the digital image of the demonstration of the powering of the calculator. Hence the fabrication of the PVDF-BTO CFs based flexible nanogenerator paves the way towards a sustainable power source and a promising entrant for designing self-power applications. Figure S2a shows the result of the manual bending test: as the device is flexible, it could easily bend and produce an electrical output. Figure S2b,c show the electrical response of the device while performing an exercise like a basic squat exercise. The device generated an electrical voltage of 6 V and a current of 19 nA, demonstrating that the presented PENG device can be used for counting the number of times the exercise was performed.

Conclusion
The PVDF-BTO composite films are highly flexible and synthesized via cost-effective processing known as the solvent casting route. The XRD pattern confirms the crystallinity features, and the surface morphology suggests that the particles are uniformly distributed upon the PVDF. The BTO particles crystallize with tetragonal symmetry. The dielectric constant increases with the doping of the BTO particles into the PVDF, showing that there are dipole-dipole interactions. Individual PENG devices are tested after the polling condition. The PNG10 device delivers an output of voltage 7.2 V and 38 nA. An instantaneous power density of 0.8 μW/cm 2 at a matching resistance of 100 MΩ is achieved from the PNG10 device. The stable output of the device can be seen from the continuous charging and discharging curve of the commercial capacitor. The PENG device can power up the calculator via a bridge rectifier, switch, and charging capacitor of 10 μF. The proposed device fabrication is adaptable and straightforward to harness energy from different vibrations or motions in the environment. It is many benefits like eco-friendly, cost-effective, and easily scalable methods to meet the power requirements of micro/nano electronic devices in the future.
Supplementary Materials: The following are available online at www.mdpi.com/xxx/s1, Figure S1: (a) A particle size distribution histogram determined from the SEM images of BTO particles ; (b) P-E hysteresis loop of PVDF and PVDF-BTO (10 wt%), Figure S2: (a) Electrical response of the PENG device upon the hand bending; (b,c) voltage and current of the PENG device upon the repetitive Squat exercise Table S1: Comparison of the piezoelectric nanogenerator based on polymer ceramic composites; device output and composite film preparation.

Conclusions
The PVDF-BTO composite films are highly flexible and synthesized via cost-effective processing known as the solvent casting route. The XRD pattern confirms the crystallinity features, and the surface morphology suggests that the particles are uniformly distributed upon the PVDF. The BTO particles crystallize with tetragonal symmetry. The dielectric constant increases with the doping of the BTO particles into the PVDF, showing that there are dipole-dipole interactions. Individual PENG devices are tested after the polling condition. The PNG10 device delivers an output of voltage 7.2 V and 38 nA. An instantaneous power density of 0.8 µW/cm 2 at a matching resistance of 100 MΩ is achieved from the PNG10 device. The stable output of the device can be seen from the continuous charging and discharging curve of the commercial capacitor. The PENG device can power up the calculator via a bridge rectifier, switch, and charging capacitor of 10 µF. The proposed device fabrication is adaptable and straightforward to harness energy from different vibrations or motions in the environment. It is many benefits like eco-friendly, cost-effective, and easily scalable methods to meet the power requirements of micro/nano electronic devices in the future.
Supplementary Materials: The following are available online at https://www.mdpi.com/2073-435 2/11/2/85/s1, Figure S1: (a) A particle size distribution histogram determined from the SEM images of BTO particles; (b) P-E hysteresis loop of PVDF and PVDF-BTO (10 wt%), Figure S2: (a) Electrical response of the PENG device upon the hand bending; (b,c) voltage and current of the PENG device upon the repetitive Squat exercise Table S1: Comparison of the piezoelectric nanogenerator based on polymer ceramic composites; device output and composite film preparation.