Properties of Nanogenerator Materials for Energy-Harvesting Application

Advancements in nanotechnology and materials science have led to the development of a variety of nanogenerator materials with improved properties, making energy harvesting technologies increasingly viable for various applications, such as powering wearable devices, remote sensors, and even small electronic gadgets in the future. The evolution of hybrid materials consisting of polymers and nanoparticles as efficient energy harvesters and energy storage devices is in high demand nowadays. Most investigations on organic ferroelectric P(VDF-TrFE) as a polymer host of polymer nanocomposite devices were primally focused on the β phase due to its excellent electrical properties for various application purposes. Nanofiller is also introduced into the polymer host to produce a polymer nanocomposite with enhanced properties. A brief description of various physical quantities related to ferroelectric, dielectric, pyroelectric effects and Thermally Stimulated Current (TSC) for energy harvesting applications in nanogenerator materials is presented. This article explores the different materials and uses of various nanogenerators. It explains the basics of the pyroelectric effect and the structure of pyroelectric nanogenerators (PNGs), as well as recent advancements in micro/nanoscale devices. Additionally, it discusses how the performance of ferroelectric, dielectric, pyroelectric, and TSC are impacted by the annealing treatment of P(VDF-TrFE) polymer

A Flexible Proximity Sensor Fully Fabricated by Inkjet Printing

A flexible proximity sensor fully fabricated by inkjet printing is proposed in this paper. The flexible proximity sensor is composed of a ZnO layer sandwiched in between a flexible aluminum sheet and a web-shaped top electrode layer. The flexible aluminum sheet serves as the bottom electrode. The material of the top electrode layer is nano silver. Both the ZnO and top electrode layers are deposited by inkjet printing. The fully inkjet printing process possesses the advantages of direct patterning and low-cost. It does not require photolithography and etching processes since the pattern is directly printed on the flexible aluminum sheet. The prototype demonstrates that the presented flexible sensor is sensitive to the human body. It may be applied to proximity sensing or thermal eradiation sensing

Large ferro–pyro–phototronic effect in 0.5Ba(Zr0.2Ti0.8)O3–0.5(Ba0.7Ca0.3)TiO3 thin films integrated on silicon for photodetection

Coupling together the ferroelectric, pyroelectric, and photovoltaic characteristics within a single material is a novel way to improve the performance of photodetectors. In this work, we take advantage of the triple multifunctionality shown by 0.5Ba(Zr0.2Ti0.8)O3–0.5(Ba0.7Ca0.3)TiO3 (BCZT), as demonstrated in an Al/Si/SiOx/BCZT/ITO thin-film device. The Si/SiOx acts as an n-type layer to form a metal–ferroelectric–insulator–semiconductor heterostructure with the BCZT, and with Al and ITO as electrodes. The photo-response of the device, with excitation from a violet laser (405 nm wavelength), is carefully investigated, and it is shown that the photodetector performance is invariant with the chopper frequency owing to the pyro-phototronic effect, which corresponds to the coupling together of the pyroelectric and photovoltaic responses. However, the photodetector performance was significantly better than that of the devices operating based only on the pyro-phototronic effect by a factor of 4, due to the presence of ferroelectricity in the system. Thus, after a poling voltage of −15 V, for a laser power density of 230 mW/cm2 and at a chopper frequency of 400 Hz, optimized responsivity, detectivity, and sensitivity values of 13.1 mA/W, 1.7 × 1010 Jones, and 26.9, respectively, are achieved. Furthermore, ultrafast rise and fall times of 2.4 and 1.5 µs, respectively, are obtained, which are 35,000 and 36,000 times faster rise and fall responses, respectively, than previous reports of devices with the ferro–pyro–phototronic effect. This is understood based on the much faster ferroelectric switching in ferroelectric thin films owing to the predominant 180° domains in a single direction out of plane.This work was supported by the Portuguese Foundation for Science and Technology (FCT) in the framework of the Strategic Funding Contracts UIDB/04650/2020. This project has received funding from the European Union's Horizon 2020 research and innovation program under grant agreement No 958174 (M-ERA-NET3/0003/2021—NanOx4EStor). The authors would also like to thank engineer José Santos for technical support at the Thin Film Laboratory. J. L. M.-D. and R. L. Z. H. are grateful for EPSRC CAM-IES grant EP/P007767/. R. L. Z. H. also acknowledges support from the Royal Academy of Engineering under the Research Fellowships scheme (No.: RF\201718\1701). J. L. M.-D. acknowledges support from the Royal Academy of Engineering Chair in Emerging Technologies scheme (No.: CIET1819_24) and the ERC grant EROS, EU-H2020-ERC-ADG # 882929

Temperature Field Analysis for PZT Pyroelectric Cells for Thermal Energy Harvesting

This paper proposes the idea of etching PZT to improve the temperature variation rate of a thicker PZT sheet in order to enhance the energy conversion efficiency when used as pyroelectric cells. A partially covered electrode was proven to display a higher output response than a fully covered electrode did. A mesh top electrode monitored the temperature variation rate and the electrode area. The mesh electrode width affected the distribution of the temperature variation rate in a thinner pyroelectric material. However, a pyroelectric cell with a thicker pyroelectric material was beneficial in generating electricity pyroelectrically. The PZT sheet was further etched to produce deeper cavities and a smaller electrode width to induce lateral temperature gradients on the sidewalls of cavities under homogeneous heat irradiation, enhancing the temperature variation rate

Improvement of Pyroelectric Cells for Thermal Energy Harvesting

This study proposes trenching piezoelectric (PZT) material in a thicker PZT pyroelectric cell to improve the temperature variation rate to enhance the efficiency of thermal energy-harvesting conversion by pyroelectricity. A thicker pyroelectric cell is beneficial in generating electricity pyroelectrically, but it hinders rapid temperature variations. Therefore, the PZT sheet was fabricated to produce deeper trenches to cause lateral temperature gradients induced by the trenched electrode, enhancing the temperature variation rate under homogeneous heat irradiation. When the trenched electrode type with an electrode width of 200 μm and a cutting depth of 150 μm was used to fabricate a PZT pyroelectric cell with a 200 μm thick PZT sheet, the temperature variation rate was improved by about 55%. Therefore, the trenched electrode design did indeed enhance the temperature variation rate and the efficiency of pyroelectric energy converters

Ferroelectric Polymer PVDF-Based Nanogenerator

This chapter deals with the development of ferroelectric polymer polyvinylidene fluoride (PVDF)-based nanogenerators. Due to its inherent flexibility, PVDF has been studied for application in nanogenerators. We first introduce PVDF and its copolymers, and briefly discuss their properties. Then, we discuss fabrication methods, including solution casting, spin coating, template-assisted method, electrospinning, thermal drawing, and dip coating. Using these methods, a wide variety of ferroelectric polymer structures can be fabricated. In addition to the performance enhancements provided by fabrication methods, the performance of PVDF-based nanogenerators has been improved by incorporating fillers that can alter the factors affecting the performance. Next, we review energy sources that can be exploited by PVDF-based nanogenerators to harvest electricity. The abundant energy sources in the environment include sound, wind flow, and thermal fluctuation. Finally, we discuss implantable PVDF-based nanogenerators. Another advantage of PVDF is its biocompatibility, which enables implantable nanogenerators. We believe that this chapter can also be helpful to researchers who study sensors and actuators as well as nanogenerators

Thermal energy harvesting using pyroelectric-electrochemical coupling in ferroelectric materials

Recently, the coupling of ferroelectrics with electrochemical reactions has attracted increasing interest for harvesting waste heat. The change of polarisation of a ferroelectric with temperature can be used to influence chemical reactions, especially when the material is cycled near its Curie temperature. In this perspective, we introduce the principle of pyroelectric controlled electrochemical processes by harvesting waste heat energy and explore their potential electrochemical applications, such as water treatment, air purificiation and hydrogen generation. As an emerging approach for driving electrochemical reactions, the presence of thermal fluctuations and/or transient waste heat in the environment has the potential to be the primary thermal input for driving the change in polarisation of a pyroelectric to release charge for such reactions. There are a number of avenues to explore and we summarize strategies for forming multi-functional or hybrid materials and future directions such as selecting pyroelectrics with low Curie temperature (< 100 {\deg}C), improved heat conductivity, enhanced surface area or porosity, tailored microstructures and systems capable of operating over a broader temperature range

Functional-Material-Based Touch Interfaces for Multidimensional Sensing for Interactive Displays: A Review

Multidimensional sensing is a highly desired attribute for allowing human-machine interfaces (HMIs) to perceive various types of information from both users and the environment, thus enabling the advancement of various smart electronics/applications, e.g., smartphones and smart cities. Conventional multidimensional sensing is achieved through the integration of multiple discrete sensors, which introduces issues such as high energy consumption and high circuit complexity. These disadvantages have motivated the widespread use of functional materials for detecting various stimuli at low cost with low power requirements. This work presents an overview of simply structured touch interfaces for multidimensional (x-y location, force and temperature) sensing enabled by piezoelectric, piezoresistive, triboelectric, pyroelectric and thermoelectric materials. For each technology, the mechanism of operation, state-of-the-art designs, merits, and drawbacks are investigated. At the end of the article, the author discusses the challenges limiting the successful applications of functional materials in commercial touch interfaces and corresponding development trends