- Email: [email protected]
A novel ZnPc nanorod derived piezoelectric nanogenerator for energy harvesting
Journal Pre-proof A novel ZnPc nanorod derived piezoelectric nanogenerator for energy harvesting D. Godfrey, D. Nirmal, L. Arivazhagan, Rathesh Kannan, Issac Nelson, S. Rajesh, B. Vidhya, N. Mohankumar PII:
S1386-9477(19)30394-7
DOI:
https://doi.org/10.1016/j.physe.2019.113931
Reference:
PHYSE 113931
To appear in:
Physica E: Low-dimensional Systems and Nanostructures
Received Date: 9 March 2019 Revised Date:
20 December 2019
Accepted Date: 23 December 2019
Please cite this article as: D. Godfrey, D. Nirmal, L. Arivazhagan, R. Kannan, I. Nelson, S. Rajesh, B. Vidhya, N. Mohankumar, A novel ZnPc nanorod derived piezoelectric nanogenerator for energy harvesting, Physica E: Low-dimensional Systems and Nanostructures (2020), doi: https:// doi.org/10.1016/j.physe.2019.113931. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2019 Published by Elsevier B.V.
A Novel ZnPc Nanorod derived Piezoelectric Nanogenerator for Energy Harvesting Godfrey D1, D. Nirmal1, L. Arivazhagan1, Rathesh Kannan1, Issac Nelson1, Rajesh S1, Vidhya B1 and N.Mohankumar2 1
Karunya Institute of Technology and Sciences, Coimbatore, India. 2 GITAM University, Bengaluru, India
Abstract: Harvesting mechanical energy into electrical energy is initially derived through Zinc Oxide (ZnO) and Gallium Nitride (GaN) nanorods by its piezoelectric nature. This paper reports on the fabricated Zinc phthalocyanine (ZnPc) nanorods on flexible Aluminum foil (Al) based nanogenerators for the first time. Aluminum foil (Al) acts as a bottom electrode as well as substrate for the growth of nanorods; whereas the top electrode is a Fluorine doped tin oxide (FTO) coated on glass substrate. Top electrode Fluorine doped tin oxide (FTO) was tapped and rubbed on the ZnPc nanorods to produce electric current. The open circuit voltage (VOC) is observed and analyzed for 100 nm and 300 nm ZnPc nanorods. The average open circuit voltage (VOC) for 100 nm, 300 nm ZnPc nanorods thickness is given as 0.524mV and 0.968mV respectively. Due to its simple fabrication method, less cost, high output gain and biocompatibility, Zinc phthalocyanine (ZnPc) Nanorods approach is suitable alternate for the ZnO nanorods in Nanogenerator devices. Keywords: Nanogenerators, ZnPc, Nanorods, Piezoelectricity, biocompatibility, ZnO 1. Introduction: In the past decades, the researchers focus is on renewable energy sources for replacing fossil fuels such as coal, crude oil and natural gases. Nanogenerators have received great attention due to its capability of production of electricity from biomechanical motions, vibrations, thermal, human motion and acoustic energies. Recently, Researchers are developing self-powered nano devices and sensors that are powered using nanogenerators [1]. Since Z.L. Wang invented triboelectric nanogenerators (TENG) various research works focused on its structures, materials, and applications are carried out. The application on various fields includes blue-energy harvesting, and self-powered sensors and selfpowered biomedical devices based on triboelectric nanogenerators (TENG) [2]. The principle of triboelectric nanogenerators works on coupling of oppositely polarized triboelectric materials to contact charging and electrostatic induction [3]. Triboelectric nanogenerators have some applications as self-powered pressure sensors, wearable respiratory energy harvesters, and self-powered motion tracking system, and self-charging tensile nanogenerators [4-8]. Piezo electric nanogenerators have the structure of piezoelectric materials merged between two electrodes. When the mechanical force is applied by the top electrode FTO or upon stretching the device, Piezo electric potential is created between the electrodes, Piezo-potential produced by Piezo electric materials such as ZnO, GaN separates the negative charges to bottom electrode. When mechanical stress is removed the
charges moves backs to its original state. Upon stretching and releasing the positive and negative electric charges are produced by piezoelectric nanogenerators simultaneously [9]. Wang et al. introduced the ZnO nanorods as first piezoelectric material for nanogenerators in 2008. From then, research on materials for piezoelectric nanogenerators have started. The materials exhibiting piezoelectric property are Lead zirconate titanate (PZT), Polyvinylidene fluoride (PVDF), Sodium bismuth titanate, barium nitride, BZT-BCT, and PMT-PT ceramic Polymers including ZnO and GaN nanorods [10-11]. Zinc phthalocyanines (ZnPc) with wider absorption region have more applications in the organic photovoltaic (OPV) devices. The main characteristics of ZnPc are the ohmic conductivity at low voltage conditions and electrical conductivity depends on the substrate temperature and thermal activation energy [12]. The phase transition of α -phase to stable β –phase of ZnPc makes the shape variation from spherical to the nanorods structure. Hybrid structure formed between the ITO and zinc phthalocyanine shows the electrical conductivity on photovoltaic applications [13]. In this work, ZnPc based piezoelectric nanogenerator (PENG) were designed and fabricated from Zinc phthalocyanine (ZnPc) and Fluorine doped tin oxide (FTO) through Physical Vapor Deposition (PVD). Al foil is used in PVD for the growth of ZnPc, which acts as the bottom electrode and substrate and reduces the complexity of electrode coating process. Fluorine doped tin oxide coated on the glass electrode acts as top electrode. The Scanning Electron Microscope (SEM) image depicts the surface morphology of ZnPc nanorods and Fluorine doped tin oxide (FTO) with respective electrodes. The electrode behavior of FTO, Average output voltage and open circuit voltage (VOC) measured via source meter. The mono crystalline structure peak for Zinc phthalocyanine at Al foil is plotted via X-Ray diffraction method. The detailed methodology, material analysis and electrical study are discussed in the next section. 2. Nanogenerator Design The physical design of ZnPc nanorods derived nanogenerator comprises of a ZnPc nanorods, bottom and top electrodes (FTO and Al). Flexible Aluminum foil (Al) with the area of 4 cm2 and thickness of 0.16 mm is used as substrate and bottom electrode. Zinc phthalocyanine (ZnPc) nanorods with the dimension of 0.1 µm, 0.3 µm was grown on the top of whole substrate (Al foil) using physical vapor deposition (PVD). Top electrode Fluorine doped tin oxide (FTO) is deposited on glass substrate until it reaches the thickness of 300nm.
Fig 1: Block Diagram of ZnPc Derived Nanogenerator
In the ZnPc nanogenerator, FTO top electrode with work function of 4.9eV forms Schottky contact with the ZnPc nanorods. On the other hand, Al foil bottom electrode with work function of 4.2eV forms the ohmic contact with the ZnPc nanorods [14]. 3. Operation Procedure Mechanism of voltage generation by ZnPc nanorods is illustrated in fig2. When mechanical rubbing force is applied to the ZnPc nanorods by FTO, piezoelectric positive and negative potentials are created at stretched side and compressed side of the ZnPc nanorods. But the electrons will not cross the ZnPc-FTO interface due to schottky barrier. When FTO electrode rubbed across the top of ZnPc nanorods and touches the compressed side of the nanorods, the negative piezoelectric potential sets the Schottky barrier to forward bias, thus in the accumulation of electron on the interface, resulting in Voltage generation in the external load[15-16].The Piezo-potential distribution is driven by Poisson’s equation as
ଶ ߮ ൌ െ
ఘ క
(1)
where ߮ - potential, ρ - inductive charge density, ξ - dielectric constant [17].
Fig 2: Working procedure with rubbing FTO on top of ZnPc nanorods a) ZnPc nanogenerator device. b) FTO electrode is rubbed on ZnPc nanorods towards right side. c) Single ZnPc nanorod operation: stretching side generates positive and compressive side generates negative Piezo electric potential. d) FTO electrode is rubbed on ZnPc nanorods towards left side and captures the electrons from nanorods . Young’s modulus equation for stress and strain is given as S=T/E (2) Where E - Young’s modulus (modulus of elasticity), T - external stress and S - the strain[17]. ZnO nanostructures such as nanorods, nanoneedles, nanoflakes, nanobricks, nanotubes, nanoflowers and nanosheets has developed for wide range of piezoelectric nanogenerators[18]. In this work, ZnPc
nanorods growth was studied for 100 nm and 300 nm rod thickness. Organic nature of the 300 nm ZnPc shows high stability and ductility compared to 100 nm nanorods[12]. 4. Experimental Section Fabrication of ZnPc on Al foil ZnPc raw material with purity of 98% is obtained in powder form and used for the growth of ZnPc nanorods on top of aluminum foil (Al). ZnPc is deposited on Al foil by physical vapor deposition (PVD) technique. The fabricated sample of ZnPc thin film has an active area of 2 cm2 and thickness of 0.3 µm. The procedure of the experiment as follows: The ZnPc powder was evaporated from a molybdenum boat onto aluminum foil substrate. Throughout the deposition process, In situ quartz crystal unit (Model-DTM 101) prefixed in PVD continuously monitors the evaporation rate and thickness of film. The ZnPc were evaporated at a pressure of 10−3 Pa that was maintained at room temperature. The whole fabrication process of ZnPc film takes place with hind vacuum coating unit (Model 12A4D). Fabrication of FTO on Glass 0.16 M of Tin(IV)chloride pentahydrate (SnCl4·5H2O) and 0.04 M NH4F was dissolved in ethanol and water respectively. Both solutions were mixed thoroughly and stirred ultrasonically for 45 minutes. An aerosol was formed and sprayed onto the heated glass substrate at 450 0 C surface temperature using HOLMARC Spray Pyrolysis Unit (Model HO-TH-04 SPD). Precursor solution is sent to hot substrate with the flow rate of 1.20 mL/min and deposited at the rate of 16-20 nm/min. The whole process continues until thickness of the FTO thin film reaches 300 nm. 5. Characterization and Electrical studies The fabricated ZnPc device is characterized with X-ray diffraction analysis, scanning electron microscope and Open circuit voltage (VOC) measurements of the ZnPc nanogenerator also carried out. A) SEM Morphology studies The surface morphological effects on ZnPc deposited on flexible aluminum foil substrate were studied using JEOL(JSM7800) scanning electron microscopy.
a)
b)
Fig 3: SEM Image a) ZnPc Nanorods with thickness of 100 nm b) ZnPc Nanorods with thickness of 300 nm
As shown in Fig. 3a and 3b, the SEM images of displays thickness of 100 and 300 nm grown ZnPc nanorods, respectively. The samples were mounted with carbon tape and gold sputtered prior to analysis. The ZnPc were analyzed at 20 kV, and imaged at 30,000× magnification, except the 300 nm ZnPc, which was imaged with 1 μm-pore size and 10,000 × magnifications. The alignment of the ZnPc nanorods in the SEM image (Fig. 3b) shows the overlapping of uniform and well-aligned bulk of ZnPc nanorods. B) X-ray Diffraction (XRD) Analysis X-ray diffraction analysis was carried out for the prepared ZnPc nanorods. The peaks at (2 0 0) planes confirms the XRD pattern of ZnPc nanorods and Al foil substrate, respectively. JCPDS number matched with the diffraction pattern of ZnPc film and shows monoclinic crystalline structure with diffraction peak at 2θ =6.7°. The peak at 44.5° with (2 0 0) orientation relates the cubic structure of corresponding Al foil with JCPDS no. 65-2869. X-ray diffraction analysis (Shimadzu XRD-6000) using Cu Kα (λ=1.5406 Å or 0.15406nm) radiation in the range between 5° and 50° is used for the device structural analysis. We have calculated the grain size of the ZnPc nanorods for 100 nm and 300 nm as 18 nm and 21 nm respectively, using The Scherrer Equation. where the Peak width (B) is inversely proportional to crystallite size (L). The stress and strain of the film is driven by various aspects such as defection lattice, dissimilar expansion and bending between the nanorods and substrate.
Fig. 4 XRD spectra of 300 nm thickness ZnPc C) Electrical studies Keithley 2401 source meter experimental testing setup is used to measure the Open circuit voltage. The voltage sweep is given from 0.1 to 1 V and maximum voltage generated from the nanogenerator is recorded by applying bias current as 0.1mA. The electron flow is controlled by the Schottky barrier between the ZnPc and FTO electrode interfaces. Time interval versus generated voltage is recorded for every 20s until 100s. The ZnPc coated with the 100 nm was initially rubbed with FTO and generated Piezo voltage is 0.524mV (fig. 5a). Due to the higher contact points in 300 nm nanorods, rubbing of FTO makes each protrusion from the ZnPc nanorods gives average output voltage as 0.968mV. The current density generated by 100 nm and 300nm ZnPc nanogenerator is current of 70 nA and 92 nA
respectively. Here the ZnPc energy conversion efficiency is 7 - 13%, the lower energy conversion is because of its deformation of nanorods and organic properties. Eventhough the efficiency of conversion is lower, the property of electron transport and absorption of electron in the ZnPc drives the output voltage to be higher compared to ZnO nanorods. Poole-Frankel effect of conduction appears on the ZnPc rods which is responsible for the dispersion of electrons in the ZnPc medium. [22]. The Average Piezo voltage generated in ZnPc nanogenerator is higher than the ZnO nanorods based nanogenerators[15].
Fig. 5 Rectified Open circuit voltage a) ZnPc Nanorods with thickness of 100 nm b) ZnPc Nanorods with thickness of 300 nm. Equation for contact potential difference (CPD) between the FTO top electrode and the ZnPc nanorods is derived as[19] Power output W = (V 2peak / R)
(3)
Fig. 6 Open circuit voltage without rubbing interval (24 -28)s, (70 -76)s and (89 -92)s Open circuit voltage is analyzed, when the process of rubbing and tapping is held for some time interval and the Open circuit voltage without rubbing interval (24 -28)s, (70 -76)s and (89 -92)s shows the least flow (Fig 6). Improvement in Electrical parameters is corresponding to increased grain size (D) and the
crystalline behavior of the 300nm ZnPc[20]. Electrical conductivity is found to be enhanced considerably for β-phase with respect to α-phase of ZnPc nanorods. Observed Piezo electric voltage is due to the monoclinic crystalline property of the ZnPc[21]. Here ZnPc monocrystalline nanorods shows better charge carrier transport leads to higher the piezo electric properties. 6. Conclusion The paper demonstrates a novel ZnPc nanorods derived nanogenerator for the first time. ZnPc on Al foil film is prepared using Physical Vapor Deposition (PVD) at a pressure of 10−3 Pa and FTO/ glass electrode is prepared using spray pyrolysis process at 450°C. Moreover, increased electrical output voltage is obtained through increasing the nanorod thickness of ZnPc from 100 nm to 300 nm. The maximum voltage of the fabricated Nanogenerator (NG) is 1.2 V which is 1.5 times more than the 100 nm size ZnPc nanorods. The presented work on organic, bio-compatible and eco-friendly ZnPc provides a plenty of room for future Nanogenerator devices. 7. References [1] Kaur, N., and Pal, K. “Triboelectric Nanogenerators for Mechanical Energy Harvesting,” Energy Technology, 6(6), pp 958–997, (2018). doi:10.1002/ente.201700639. [2] Z. L. Wang, J. Chen, and L. Lin. “Progress in triboelectric nanogenerators as a new energy technology and self-powered sensors,” RSC Energy Environ. Sci., 8, pp 2250--2282, (2015). [3] Zi, Y. et al. “Effective energy storage from triboelectric nanogenerator,” Nat. Commun., 7:10987, (2016). doi: 10.1038/ncomms10987. [4] P.K. Yang, Z. H. Lin, K. C. Pradel, L. Lin,X. Li,X. Wen,J.H.He and Z. L. Wan. “Paper-Based Origami Triboelectric Nanogenerators and Self-Powered Pressure Sensors,” ACS Nano, 9, 1, pp 901-907, (2015). https://doi.org/10.1021/nn506631t. [5] P. Vasandani, B. Gattu, J. Wu, Z. H. Mao, W. Jia, and M. Sun. “Triboelectric Nanogenerator Using Microdome-Patterned PDMS as a Wearable Respiratory Energy Harvester,” Adv Mat. Tech., 2, 1700014, (2017). doi: 10.1002/admt.201700014. [6] M. Chen, X. Li, L. Lin, W. Du , X. Han, J. Zhu, C. Pan, and Z. L. Wang .“Triboelectric Nanogenerators as a Self-Powered Motion Tracking System,” Adv Fun. Mat., 24, pp 5050-5066, (2014). doi: 10.1002/adfm.201400431. [7] X. Pu, L. Li, H. Song, C. Du, Z. Zhao, C. Jiang, G. Cao, W. Hu, and Z. L. Wang. “A Self-Charging Power Unit by Integration of a Textile Triboelectric Nanogenerator and a Flexible Lithium-Ion Battery for Wearable Electronics,” Adv. Mater., 27, pp 2472-2478, (2015). doi:10.1002/adma.201500311. [8] Shi, Q. et al. “MEMS Based Broadband Piezoelectric Ultrasonic Energy Harvester (PUEH) for Enabling Self-Powered Implantable Biomedical Devices,” Sci. Rep. 6, 24946, (2016), doi: 10.1038/srep24946. [9] Briscoe, Joe and Dunn, Steve. “Piezoelectric nanogenerators – a review of nanostructured piezoelectric energy harvesters,” Nano Energy, 14, pp 15-29, (2015). doi:10.1016/j.nanoen.2014.11.059. [10] F. R. Fan, W. Tang, and Z. L. Wang. “Flexible Nanogenerators for Energy Harvesting and SelfPowered Electronics,” Adv. Mat., 28, pp. 4283–4305, (2016). doi: 10.1002/adma.201504299.
[11] Chen, X., Li, X., Shao, J., An, N., Tian, H., Wang, and C.,Lu, B.“High- Performance Piezoelectric Nanogenerators with Imprinted P(VDF-TrFE)/BaTiO3 Nanocomposite Micropillars for SelfPowered Flexible Sensors,” Small, 13, 1604245, (2017). doi:10.1002/small.201604245. [12] Singh, S., Saini, G. S. S., and Tripathi, S. K. “Sensing properties of ZnPc thin films studied by electrical and optical techniques,” Sensors and Actuators B: Chemical, 203, pp 118–121, (2014). doi:10.1016/j.snb.2014.06.084. [13] Kadem, B., Hassan, A., Göksel, M., Basova, T., Şenocak, A., Demirbaş, E., and Durmuş, M. “High performance ternary solar cells based on P3HT: PCBM and ZnPc-hybrids,” RSC Advances, 6(96), pp 93453–93462, (2016). Doi:10.1039/c6ra17590b. [14] R. Zhang, M. Hummelgård, M. Olsen, J. Örtegren and H. Olin., “Nanogenerator made of ZnO nanosheet networks,” Semicond. Sci. Tech. 32, 054002,(2017). doi: 10.1088/13616641/aa660c. [15] Zhong Lin Wang, and Jinhui Song. “Piezoelectric Nanogenerators Based on Zinc Oxide Nanowire Arrays,” SCIENCE, 312, pp 242-246, (2006). doi: 10.1126/science.1124005. [16] Wang, X., Song, J., Liu, J., and Wang, Z. L.“Direct-Current Nanogenerator Driven by Ultrasonic Waves. Science,” 316(5821), pp 102–105, (2007). doi:10.1126/science.1139366. [17] Huang X, Li L J, and Zhang Y. “Modeling the open circuit output voltage of piezoelectric nanogenerator,” Sci China Tech. Sci, 56, pp 2622-2629, (2013). doi:10.1007/s11431-013-53529. [18] A. Khan, M. A. Abbasi, J. Wissting, O. Nur, and M. Willander. “Harvesting piezoelectric potential from zinc oxide nanoflowers grown on textile fabric substrate,” Phys. Status Solidi. RRL 7, 11, pp. 980–984, (2013). doi: 10.1002/pssr.201308105. [19] H. J. Kim, J. H. Kim, K. W. Jun, J. H. Kim, W. C. Seung, O. H. Kwon, J. Y. Park, S. W. Kim, and I. K. Oh.“Silk Nanofiber-Networked Bio-Triboelectric Generator: Silk Bio-TEG,” Small, 6, 150232, (2016). doi:10.1002/aenm.201502329. [20] Senthilarasu, S., Hahn, Y. B., and Lee, S.-H. “Structural analysis of zinc phthalocyanine (ZnPc) thin films: X-ray diffraction study,” Journal of Applied Physics, 102(4), 043512, (2007). doi:10.1063/1.2771046. [21] Hwang, G.-T., Park, H., Lee, J.-H., Oh, S., Park, K.-I., Byun, M., and Lee, K. J. “Self-Powered Cardiac Pacemaker Enabled by Flexible Single Crystalline PMN-PT Piezoelectric Energy Harvester,” Advanced Materials, 26(28), pp 4880–4887, (2014). doi:10.1002/adma.201400562. [22]Sundaram, S. Sathyamoorthy, R.Lalitha, S. & Subbarayan, A. “Electrical conduction properties of ZnPc/TiO2 thin films,” Solar Energy Materials and Solar Cells. 90. 783-797. (2006). 10.1016/j.solmat.2005.04.015.
HIGHLIGHTS
A novel Zinc phthalocyanine (ZnPc) nanorods based nanogenerators is fabricated and performance was analyzed. Zinc phthalocyanine (ZnPc) nanorods are grown on flexible Aluminum foil (Al) substrate and the morphology and crystalline properties was analyzed using SEM and XRD. The average open circuit voltage (VOC) for 100 nm, 300 nm ZnPc nanorods thickness is measured using source meter. Performance of ZnPc nanogenerator is investigated with higher output voltage than ZnO based nanogenerators.
Author Statement To The Editor in Chief Physica E: Low Dimensional systems and nanostructures
Dear Editor Authors of the article titled “A Novel ZnPc Nanorod derived Piezoelectric Nanogenerator for Energy Harvesting” certify that neither this manuscript nor one with substantially similar content under this authorship has been published or being considered for publishing elsewhere in any language.
Regards D. Nirmal Associate professor and Headof ECE, Karunya institute of technology and sciences, India, 641114.
S1386-9477(19)30394-7
DOI:
https://doi.org/10.1016/j.physe.2019.113931
Reference:
PHYSE 113931
To appear in:
Physica E: Low-dimensional Systems and Nanostructures
Received Date: 9 March 2019 Revised Date:
20 December 2019
Accepted Date: 23 December 2019
Please cite this article as: D. Godfrey, D. Nirmal, L. Arivazhagan, R. Kannan, I. Nelson, S. Rajesh, B. Vidhya, N. Mohankumar, A novel ZnPc nanorod derived piezoelectric nanogenerator for energy harvesting, Physica E: Low-dimensional Systems and Nanostructures (2020), doi: https:// doi.org/10.1016/j.physe.2019.113931. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2019 Published by Elsevier B.V.
A Novel ZnPc Nanorod derived Piezoelectric Nanogenerator for Energy Harvesting Godfrey D1, D. Nirmal1, L. Arivazhagan1, Rathesh Kannan1, Issac Nelson1, Rajesh S1, Vidhya B1 and N.Mohankumar2 1
Karunya Institute of Technology and Sciences, Coimbatore, India. 2 GITAM University, Bengaluru, India
Abstract: Harvesting mechanical energy into electrical energy is initially derived through Zinc Oxide (ZnO) and Gallium Nitride (GaN) nanorods by its piezoelectric nature. This paper reports on the fabricated Zinc phthalocyanine (ZnPc) nanorods on flexible Aluminum foil (Al) based nanogenerators for the first time. Aluminum foil (Al) acts as a bottom electrode as well as substrate for the growth of nanorods; whereas the top electrode is a Fluorine doped tin oxide (FTO) coated on glass substrate. Top electrode Fluorine doped tin oxide (FTO) was tapped and rubbed on the ZnPc nanorods to produce electric current. The open circuit voltage (VOC) is observed and analyzed for 100 nm and 300 nm ZnPc nanorods. The average open circuit voltage (VOC) for 100 nm, 300 nm ZnPc nanorods thickness is given as 0.524mV and 0.968mV respectively. Due to its simple fabrication method, less cost, high output gain and biocompatibility, Zinc phthalocyanine (ZnPc) Nanorods approach is suitable alternate for the ZnO nanorods in Nanogenerator devices. Keywords: Nanogenerators, ZnPc, Nanorods, Piezoelectricity, biocompatibility, ZnO 1. Introduction: In the past decades, the researchers focus is on renewable energy sources for replacing fossil fuels such as coal, crude oil and natural gases. Nanogenerators have received great attention due to its capability of production of electricity from biomechanical motions, vibrations, thermal, human motion and acoustic energies. Recently, Researchers are developing self-powered nano devices and sensors that are powered using nanogenerators [1]. Since Z.L. Wang invented triboelectric nanogenerators (TENG) various research works focused on its structures, materials, and applications are carried out. The application on various fields includes blue-energy harvesting, and self-powered sensors and selfpowered biomedical devices based on triboelectric nanogenerators (TENG) [2]. The principle of triboelectric nanogenerators works on coupling of oppositely polarized triboelectric materials to contact charging and electrostatic induction [3]. Triboelectric nanogenerators have some applications as self-powered pressure sensors, wearable respiratory energy harvesters, and self-powered motion tracking system, and self-charging tensile nanogenerators [4-8]. Piezo electric nanogenerators have the structure of piezoelectric materials merged between two electrodes. When the mechanical force is applied by the top electrode FTO or upon stretching the device, Piezo electric potential is created between the electrodes, Piezo-potential produced by Piezo electric materials such as ZnO, GaN separates the negative charges to bottom electrode. When mechanical stress is removed the
charges moves backs to its original state. Upon stretching and releasing the positive and negative electric charges are produced by piezoelectric nanogenerators simultaneously [9]. Wang et al. introduced the ZnO nanorods as first piezoelectric material for nanogenerators in 2008. From then, research on materials for piezoelectric nanogenerators have started. The materials exhibiting piezoelectric property are Lead zirconate titanate (PZT), Polyvinylidene fluoride (PVDF), Sodium bismuth titanate, barium nitride, BZT-BCT, and PMT-PT ceramic Polymers including ZnO and GaN nanorods [10-11]. Zinc phthalocyanines (ZnPc) with wider absorption region have more applications in the organic photovoltaic (OPV) devices. The main characteristics of ZnPc are the ohmic conductivity at low voltage conditions and electrical conductivity depends on the substrate temperature and thermal activation energy [12]. The phase transition of α -phase to stable β –phase of ZnPc makes the shape variation from spherical to the nanorods structure. Hybrid structure formed between the ITO and zinc phthalocyanine shows the electrical conductivity on photovoltaic applications [13]. In this work, ZnPc based piezoelectric nanogenerator (PENG) were designed and fabricated from Zinc phthalocyanine (ZnPc) and Fluorine doped tin oxide (FTO) through Physical Vapor Deposition (PVD). Al foil is used in PVD for the growth of ZnPc, which acts as the bottom electrode and substrate and reduces the complexity of electrode coating process. Fluorine doped tin oxide coated on the glass electrode acts as top electrode. The Scanning Electron Microscope (SEM) image depicts the surface morphology of ZnPc nanorods and Fluorine doped tin oxide (FTO) with respective electrodes. The electrode behavior of FTO, Average output voltage and open circuit voltage (VOC) measured via source meter. The mono crystalline structure peak for Zinc phthalocyanine at Al foil is plotted via X-Ray diffraction method. The detailed methodology, material analysis and electrical study are discussed in the next section. 2. Nanogenerator Design The physical design of ZnPc nanorods derived nanogenerator comprises of a ZnPc nanorods, bottom and top electrodes (FTO and Al). Flexible Aluminum foil (Al) with the area of 4 cm2 and thickness of 0.16 mm is used as substrate and bottom electrode. Zinc phthalocyanine (ZnPc) nanorods with the dimension of 0.1 µm, 0.3 µm was grown on the top of whole substrate (Al foil) using physical vapor deposition (PVD). Top electrode Fluorine doped tin oxide (FTO) is deposited on glass substrate until it reaches the thickness of 300nm.
Fig 1: Block Diagram of ZnPc Derived Nanogenerator
In the ZnPc nanogenerator, FTO top electrode with work function of 4.9eV forms Schottky contact with the ZnPc nanorods. On the other hand, Al foil bottom electrode with work function of 4.2eV forms the ohmic contact with the ZnPc nanorods [14]. 3. Operation Procedure Mechanism of voltage generation by ZnPc nanorods is illustrated in fig2. When mechanical rubbing force is applied to the ZnPc nanorods by FTO, piezoelectric positive and negative potentials are created at stretched side and compressed side of the ZnPc nanorods. But the electrons will not cross the ZnPc-FTO interface due to schottky barrier. When FTO electrode rubbed across the top of ZnPc nanorods and touches the compressed side of the nanorods, the negative piezoelectric potential sets the Schottky barrier to forward bias, thus in the accumulation of electron on the interface, resulting in Voltage generation in the external load[15-16].The Piezo-potential distribution is driven by Poisson’s equation as
ଶ ߮ ൌ െ
ఘ క
(1)
where ߮ - potential, ρ - inductive charge density, ξ - dielectric constant [17].
Fig 2: Working procedure with rubbing FTO on top of ZnPc nanorods a) ZnPc nanogenerator device. b) FTO electrode is rubbed on ZnPc nanorods towards right side. c) Single ZnPc nanorod operation: stretching side generates positive and compressive side generates negative Piezo electric potential. d) FTO electrode is rubbed on ZnPc nanorods towards left side and captures the electrons from nanorods . Young’s modulus equation for stress and strain is given as S=T/E (2) Where E - Young’s modulus (modulus of elasticity), T - external stress and S - the strain[17]. ZnO nanostructures such as nanorods, nanoneedles, nanoflakes, nanobricks, nanotubes, nanoflowers and nanosheets has developed for wide range of piezoelectric nanogenerators[18]. In this work, ZnPc
nanorods growth was studied for 100 nm and 300 nm rod thickness. Organic nature of the 300 nm ZnPc shows high stability and ductility compared to 100 nm nanorods[12]. 4. Experimental Section Fabrication of ZnPc on Al foil ZnPc raw material with purity of 98% is obtained in powder form and used for the growth of ZnPc nanorods on top of aluminum foil (Al). ZnPc is deposited on Al foil by physical vapor deposition (PVD) technique. The fabricated sample of ZnPc thin film has an active area of 2 cm2 and thickness of 0.3 µm. The procedure of the experiment as follows: The ZnPc powder was evaporated from a molybdenum boat onto aluminum foil substrate. Throughout the deposition process, In situ quartz crystal unit (Model-DTM 101) prefixed in PVD continuously monitors the evaporation rate and thickness of film. The ZnPc were evaporated at a pressure of 10−3 Pa that was maintained at room temperature. The whole fabrication process of ZnPc film takes place with hind vacuum coating unit (Model 12A4D). Fabrication of FTO on Glass 0.16 M of Tin(IV)chloride pentahydrate (SnCl4·5H2O) and 0.04 M NH4F was dissolved in ethanol and water respectively. Both solutions were mixed thoroughly and stirred ultrasonically for 45 minutes. An aerosol was formed and sprayed onto the heated glass substrate at 450 0 C surface temperature using HOLMARC Spray Pyrolysis Unit (Model HO-TH-04 SPD). Precursor solution is sent to hot substrate with the flow rate of 1.20 mL/min and deposited at the rate of 16-20 nm/min. The whole process continues until thickness of the FTO thin film reaches 300 nm. 5. Characterization and Electrical studies The fabricated ZnPc device is characterized with X-ray diffraction analysis, scanning electron microscope and Open circuit voltage (VOC) measurements of the ZnPc nanogenerator also carried out. A) SEM Morphology studies The surface morphological effects on ZnPc deposited on flexible aluminum foil substrate were studied using JEOL(JSM7800) scanning electron microscopy.
a)
b)
Fig 3: SEM Image a) ZnPc Nanorods with thickness of 100 nm b) ZnPc Nanorods with thickness of 300 nm
As shown in Fig. 3a and 3b, the SEM images of displays thickness of 100 and 300 nm grown ZnPc nanorods, respectively. The samples were mounted with carbon tape and gold sputtered prior to analysis. The ZnPc were analyzed at 20 kV, and imaged at 30,000× magnification, except the 300 nm ZnPc, which was imaged with 1 μm-pore size and 10,000 × magnifications. The alignment of the ZnPc nanorods in the SEM image (Fig. 3b) shows the overlapping of uniform and well-aligned bulk of ZnPc nanorods. B) X-ray Diffraction (XRD) Analysis X-ray diffraction analysis was carried out for the prepared ZnPc nanorods. The peaks at (2 0 0) planes confirms the XRD pattern of ZnPc nanorods and Al foil substrate, respectively. JCPDS number matched with the diffraction pattern of ZnPc film and shows monoclinic crystalline structure with diffraction peak at 2θ =6.7°. The peak at 44.5° with (2 0 0) orientation relates the cubic structure of corresponding Al foil with JCPDS no. 65-2869. X-ray diffraction analysis (Shimadzu XRD-6000) using Cu Kα (λ=1.5406 Å or 0.15406nm) radiation in the range between 5° and 50° is used for the device structural analysis. We have calculated the grain size of the ZnPc nanorods for 100 nm and 300 nm as 18 nm and 21 nm respectively, using The Scherrer Equation. where the Peak width (B) is inversely proportional to crystallite size (L). The stress and strain of the film is driven by various aspects such as defection lattice, dissimilar expansion and bending between the nanorods and substrate.
Fig. 4 XRD spectra of 300 nm thickness ZnPc C) Electrical studies Keithley 2401 source meter experimental testing setup is used to measure the Open circuit voltage. The voltage sweep is given from 0.1 to 1 V and maximum voltage generated from the nanogenerator is recorded by applying bias current as 0.1mA. The electron flow is controlled by the Schottky barrier between the ZnPc and FTO electrode interfaces. Time interval versus generated voltage is recorded for every 20s until 100s. The ZnPc coated with the 100 nm was initially rubbed with FTO and generated Piezo voltage is 0.524mV (fig. 5a). Due to the higher contact points in 300 nm nanorods, rubbing of FTO makes each protrusion from the ZnPc nanorods gives average output voltage as 0.968mV. The current density generated by 100 nm and 300nm ZnPc nanogenerator is current of 70 nA and 92 nA
respectively. Here the ZnPc energy conversion efficiency is 7 - 13%, the lower energy conversion is because of its deformation of nanorods and organic properties. Eventhough the efficiency of conversion is lower, the property of electron transport and absorption of electron in the ZnPc drives the output voltage to be higher compared to ZnO nanorods. Poole-Frankel effect of conduction appears on the ZnPc rods which is responsible for the dispersion of electrons in the ZnPc medium. [22]. The Average Piezo voltage generated in ZnPc nanogenerator is higher than the ZnO nanorods based nanogenerators[15].
Fig. 5 Rectified Open circuit voltage a) ZnPc Nanorods with thickness of 100 nm b) ZnPc Nanorods with thickness of 300 nm. Equation for contact potential difference (CPD) between the FTO top electrode and the ZnPc nanorods is derived as[19] Power output W = (V 2peak / R)
(3)
Fig. 6 Open circuit voltage without rubbing interval (24 -28)s, (70 -76)s and (89 -92)s Open circuit voltage is analyzed, when the process of rubbing and tapping is held for some time interval and the Open circuit voltage without rubbing interval (24 -28)s, (70 -76)s and (89 -92)s shows the least flow (Fig 6). Improvement in Electrical parameters is corresponding to increased grain size (D) and the
crystalline behavior of the 300nm ZnPc[20]. Electrical conductivity is found to be enhanced considerably for β-phase with respect to α-phase of ZnPc nanorods. Observed Piezo electric voltage is due to the monoclinic crystalline property of the ZnPc[21]. Here ZnPc monocrystalline nanorods shows better charge carrier transport leads to higher the piezo electric properties. 6. Conclusion The paper demonstrates a novel ZnPc nanorods derived nanogenerator for the first time. ZnPc on Al foil film is prepared using Physical Vapor Deposition (PVD) at a pressure of 10−3 Pa and FTO/ glass electrode is prepared using spray pyrolysis process at 450°C. Moreover, increased electrical output voltage is obtained through increasing the nanorod thickness of ZnPc from 100 nm to 300 nm. The maximum voltage of the fabricated Nanogenerator (NG) is 1.2 V which is 1.5 times more than the 100 nm size ZnPc nanorods. The presented work on organic, bio-compatible and eco-friendly ZnPc provides a plenty of room for future Nanogenerator devices. 7. References [1] Kaur, N., and Pal, K. “Triboelectric Nanogenerators for Mechanical Energy Harvesting,” Energy Technology, 6(6), pp 958–997, (2018). doi:10.1002/ente.201700639. [2] Z. L. Wang, J. Chen, and L. Lin. “Progress in triboelectric nanogenerators as a new energy technology and self-powered sensors,” RSC Energy Environ. Sci., 8, pp 2250--2282, (2015). [3] Zi, Y. et al. “Effective energy storage from triboelectric nanogenerator,” Nat. Commun., 7:10987, (2016). doi: 10.1038/ncomms10987. [4] P.K. Yang, Z. H. Lin, K. C. Pradel, L. Lin,X. Li,X. Wen,J.H.He and Z. L. Wan. “Paper-Based Origami Triboelectric Nanogenerators and Self-Powered Pressure Sensors,” ACS Nano, 9, 1, pp 901-907, (2015). https://doi.org/10.1021/nn506631t. [5] P. Vasandani, B. Gattu, J. Wu, Z. H. Mao, W. Jia, and M. Sun. “Triboelectric Nanogenerator Using Microdome-Patterned PDMS as a Wearable Respiratory Energy Harvester,” Adv Mat. Tech., 2, 1700014, (2017). doi: 10.1002/admt.201700014. [6] M. Chen, X. Li, L. Lin, W. Du , X. Han, J. Zhu, C. Pan, and Z. L. Wang .“Triboelectric Nanogenerators as a Self-Powered Motion Tracking System,” Adv Fun. Mat., 24, pp 5050-5066, (2014). doi: 10.1002/adfm.201400431. [7] X. Pu, L. Li, H. Song, C. Du, Z. Zhao, C. Jiang, G. Cao, W. Hu, and Z. L. Wang. “A Self-Charging Power Unit by Integration of a Textile Triboelectric Nanogenerator and a Flexible Lithium-Ion Battery for Wearable Electronics,” Adv. Mater., 27, pp 2472-2478, (2015). doi:10.1002/adma.201500311. [8] Shi, Q. et al. “MEMS Based Broadband Piezoelectric Ultrasonic Energy Harvester (PUEH) for Enabling Self-Powered Implantable Biomedical Devices,” Sci. Rep. 6, 24946, (2016), doi: 10.1038/srep24946. [9] Briscoe, Joe and Dunn, Steve. “Piezoelectric nanogenerators – a review of nanostructured piezoelectric energy harvesters,” Nano Energy, 14, pp 15-29, (2015). doi:10.1016/j.nanoen.2014.11.059. [10] F. R. Fan, W. Tang, and Z. L. Wang. “Flexible Nanogenerators for Energy Harvesting and SelfPowered Electronics,” Adv. Mat., 28, pp. 4283–4305, (2016). doi: 10.1002/adma.201504299.
[11] Chen, X., Li, X., Shao, J., An, N., Tian, H., Wang, and C.,Lu, B.“High- Performance Piezoelectric Nanogenerators with Imprinted P(VDF-TrFE)/BaTiO3 Nanocomposite Micropillars for SelfPowered Flexible Sensors,” Small, 13, 1604245, (2017). doi:10.1002/small.201604245. [12] Singh, S., Saini, G. S. S., and Tripathi, S. K. “Sensing properties of ZnPc thin films studied by electrical and optical techniques,” Sensors and Actuators B: Chemical, 203, pp 118–121, (2014). doi:10.1016/j.snb.2014.06.084. [13] Kadem, B., Hassan, A., Göksel, M., Basova, T., Şenocak, A., Demirbaş, E., and Durmuş, M. “High performance ternary solar cells based on P3HT: PCBM and ZnPc-hybrids,” RSC Advances, 6(96), pp 93453–93462, (2016). Doi:10.1039/c6ra17590b. [14] R. Zhang, M. Hummelgård, M. Olsen, J. Örtegren and H. Olin., “Nanogenerator made of ZnO nanosheet networks,” Semicond. Sci. Tech. 32, 054002,(2017). doi: 10.1088/13616641/aa660c. [15] Zhong Lin Wang, and Jinhui Song. “Piezoelectric Nanogenerators Based on Zinc Oxide Nanowire Arrays,” SCIENCE, 312, pp 242-246, (2006). doi: 10.1126/science.1124005. [16] Wang, X., Song, J., Liu, J., and Wang, Z. L.“Direct-Current Nanogenerator Driven by Ultrasonic Waves. Science,” 316(5821), pp 102–105, (2007). doi:10.1126/science.1139366. [17] Huang X, Li L J, and Zhang Y. “Modeling the open circuit output voltage of piezoelectric nanogenerator,” Sci China Tech. Sci, 56, pp 2622-2629, (2013). doi:10.1007/s11431-013-53529. [18] A. Khan, M. A. Abbasi, J. Wissting, O. Nur, and M. Willander. “Harvesting piezoelectric potential from zinc oxide nanoflowers grown on textile fabric substrate,” Phys. Status Solidi. RRL 7, 11, pp. 980–984, (2013). doi: 10.1002/pssr.201308105. [19] H. J. Kim, J. H. Kim, K. W. Jun, J. H. Kim, W. C. Seung, O. H. Kwon, J. Y. Park, S. W. Kim, and I. K. Oh.“Silk Nanofiber-Networked Bio-Triboelectric Generator: Silk Bio-TEG,” Small, 6, 150232, (2016). doi:10.1002/aenm.201502329. [20] Senthilarasu, S., Hahn, Y. B., and Lee, S.-H. “Structural analysis of zinc phthalocyanine (ZnPc) thin films: X-ray diffraction study,” Journal of Applied Physics, 102(4), 043512, (2007). doi:10.1063/1.2771046. [21] Hwang, G.-T., Park, H., Lee, J.-H., Oh, S., Park, K.-I., Byun, M., and Lee, K. J. “Self-Powered Cardiac Pacemaker Enabled by Flexible Single Crystalline PMN-PT Piezoelectric Energy Harvester,” Advanced Materials, 26(28), pp 4880–4887, (2014). doi:10.1002/adma.201400562. [22]Sundaram, S. Sathyamoorthy, R.Lalitha, S. & Subbarayan, A. “Electrical conduction properties of ZnPc/TiO2 thin films,” Solar Energy Materials and Solar Cells. 90. 783-797. (2006). 10.1016/j.solmat.2005.04.015.
HIGHLIGHTS
A novel Zinc phthalocyanine (ZnPc) nanorods based nanogenerators is fabricated and performance was analyzed. Zinc phthalocyanine (ZnPc) nanorods are grown on flexible Aluminum foil (Al) substrate and the morphology and crystalline properties was analyzed using SEM and XRD. The average open circuit voltage (VOC) for 100 nm, 300 nm ZnPc nanorods thickness is measured using source meter. Performance of ZnPc nanogenerator is investigated with higher output voltage than ZnO based nanogenerators.
Author Statement To The Editor in Chief Physica E: Low Dimensional systems and nanostructures
Dear Editor Authors of the article titled “A Novel ZnPc Nanorod derived Piezoelectric Nanogenerator for Energy Harvesting” certify that neither this manuscript nor one with substantially similar content under this authorship has been published or being considered for publishing elsewhere in any language.
Regards D. Nirmal Associate professor and Headof ECE, Karunya institute of technology and sciences, India, 641114.