Transparent Photovoltaics with Array ZnO/NiO Structure for Energy Harvesting and Human Interface Applications

Transparent metal-oxide photovoltaics for energy harvesting and storage for sustainable platforms

Carrier transport and working mechanism of transparent photovoltaic cells

Over the years, energy harvesting technologies have been used in various self-powered systems. These technologies have several methods of application depending on their usage. Renewable energy is one of the types of energy harvesting technologies where energy is generated from naturally replenished sources. One of the energy harvesting methods that is commonly used is piezoelectric transducers. Piezoelectric materials are groups of elements that can be used to generate electricity when mechanical energy is applied. When external mechanical stress is applied, the inner lattice is deformed, resulting in the separation of the positive and negative centers of the molecule and thus the generation of a small dipole. Therefore, this paper aims to discuss the output of the piezoelectric transducer by reviewing it depending on two different material types and in other energy harvesting structures. Furthermore, a comparison was made in order to compare the power output of the two materials. Similarly, the most used piezoelectric transducer structures for power harvesting applications were revised. In addition, the parameters that affect the value of the generated power output were discussed using the figures of merit (FOM) concept. Moreover, the according to the FOM concepts, when stress is applied, the electrical energy extracted from a piezoelectric energy harvesting material is determined by the change in stored electrical energy within a piezoelectric material. The figures of merit (FOM) depend on the piezoelectric strain and its permittivity. The piezoelectric strain directly relates to FOM, while the permittivity has an inverse relationship with FOM. Thus, the highest strain constant and low permittivity material will provide the highest energy output. Additionally, lead-based (PZT) material has a strain coefficient d33 equal to 390 Coul/Nx10-12, and permittivity value ranging from 1000 to 3500 and can generate power output that is equal to 52mW at 100Hz, which is higher than the output of the lead-free-based material Barium Titanate (BaTiO3). The output of piezoelectric also depends on the piezoelectric transducer’s structure. The circular diaphragm’s power output is greater than the bimorph cantilever’s power output due to the presence of a proof mass in the center of the diaphragm that provides prestress to the piezoelectric which improves the low-frequency performance of the energy harvester.

Over the past two decades, piezoelectric materials have become an integral part of structural health monitoring (SHM) and energy harvesting. These materials are available in various forms and configurations, yet the potential of curved configurations remains largely unexplored. This article experimentally explores the performance of singly curved thin piezoelectric transducers compared to their straight configuration when embedded in reinforced concrete (RC) structures for energy harvesting and SHM applications. The research includes a side-by-side comparison of these configurations based on (a) the open-circuit voltage generated by them under pure harmonic excitations, (b) the power generated under the impedance matching conditions, and (c) their potential for power storage in capacitors under real-life erratic vibrations with impedance mismatch conditions. Additionally, the article investigates the damage detection capabilities of curved piezo transducers using the electromechanical impedance (EMI) technique, an area that has not been thoroughly explored. The results from all four experiments demonstrate that the curved piezo transducers outperform their straight configurations in both SHM and energy harvesting applications. Therefore, the findings from these investigations are crucial for the effective utilization of curved piezoelectric transducers in real-world RC structures, enhancing both energy harvesting and structural health monitoring, which in fact, leads to the economic maintenance and safe operation of RC structures.

In this article, a novel energy harvesting (EH) interface for a flexible thin-film piezoelectric generator (FPEG) is proposed for EH from irregular human motion. The traditional thick piezoelectric generator (PEG) based kinetic EH circuits are designed for continuous and sinusoidal inputs from the cantilever-based structures and are not suitable for EH from irregular human motion. The proposed EH interface circuit significantly enhances energy extraction with a load-screening scheme, which minimizes the load capacitance to maximize the PEG output voltage up to 102 V while using the standard voltage 0.18- <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">μ</i> m process. An energy-aware wake-up controller is designed to (monitor and) detect the FPEG deformation to assure that the harvesting interface is only activated when enough energy is available for EH. When the FPEG voltage peaks, the energy is transferred to the battery through an inductor with a single-cycle buck-converter-like operation, allowing the input voltage and frequency-independent EH operation. The measurement results show that the proposed EH interface successfully harvests energy from irregular pulsed inputs with 562% improvement compared with a full-bridge rectifier.

Chapter 9 - Recent advancement in sustainable energy harvesting using piezoelectric materials

With the advancement of industrial automation, vibrational energy generated by machinery during operation is often underutilized. Developing efficient devices for vibration energy harvesting is thus essential. Triboelectric nanogenerators (TENGs) based on spring and cantilever beam structures show considerable potential for industrial vibration energy harvesting; however, traditional designs often fail to fully harness vibrational energy due to their structural limitations. This study proposes a triboelectric nanogenerator (TENG) based on a crank-rocker mechanism and a spring cantilever structure (CR-SC TENG), which combines a crank-rocker mechanism with a spring cantilever structure, designed for both energy harvesting and self-powered sensing. The CR-SC TENG incorporates a spring cantilever beam, a crank-rocker mechanism, and lever amplification principles, enabling it to respond sensitively to low-frequency, small-amplitude vibrations. Utilizing the crank-rocker and lever effects, this device significantly amplifies micro-amplitudes, enhancing energy capture efficiency and making it well suited for low-amplitude, complex industrial environments. Experimental results demonstrate that this design effectively amplifies micro-vibrations and markedly improves energy conversion efficiency within a frequency range of 1–35 Hz and an amplitude range of 1–3 mm. As a sensor, the CR-SC TENG’s dual-generation units produce output signals that precisely reflect vibration frequencies, making it suitable for the intelligent monitoring of industrial equipment. When placed on an air compressor operating at 25 Hz, the first-generation unit achieved an output voltage of 150 V and a current of 8 μA, while the second-generation unit produced an output voltage of 60 V and a current of 5 μA. These findings suggest that the CR-SC TENG, leveraging spring cantilever beams, crank-rocker mechanisms, and lever amplification, has significant potential for micro-amplitude energy harvesting and could play a key role in smart manufacturing, intelligent factories, and the Internet of Things.

The challenges in transparent photovoltaic (TPV) fields are still that the device transparency and efficiency are difficult to be balanced to meet the requirements of practical applications. In this study, we systematically investigated the interrelationship between photovoltaic film properties, optical transmission, and photovoltaic performances in the near-infrared harvesting organic TPVs. The results indicate that the photovoltaic film thickness determines the TPV’s transparency and meanwhile affects the device efficiency; by contrast, the donor–acceptor ratio only affects device efficiency and has little effect on transparency. By controlling the film thickness and donor–acceptor ratio, the average visible transmission (AVT) of TPVs can be precisely managed in the range of 40% - 85%, and the device efficiency can achieve as high as 4.06% and 2.38% while the AVT exceeds 70% and 80%, respectively. Importantly, the large area (~10 cm2) TPV modules and ultra-flexible devices were then successfully prepared based on the systematical study.

The development of "Transparent Photovoltaics" (TPVs[1]), i.e., solar cells that are transparent to visible light, has become more and more popular in recent years due to their contribution to low CO2 emissions through "window power generation" in fully glazed buildings (building-integrated photovoltaics: BIPV) and the growing demand for development in the promotion of farm-based solar power; Agrivoltaics [2, 3]. So far, selective light-transmission photovoltaics (SLTPVs), in which conventional bulk and thin-film solar cells are fabricated into long and thin strips and arranged like a window shade at intervals or by reducing the film thickness, have already been put into practical use [3, 4], allowing part of the incident light to escape to the rear. However, the installation applications of SLTPVs are limited since blocking the line of sight outside the window and preventing a sufficient amount of light from reaching the interior or farmland surface. If TPVs that are uniformly transparent or tinted-transparent like window glasses can be commercialized, the range of applications is expected to expand significantly.TPVs are perceived by humans as being "nearly colorless" if they have a visible light transmittance of 80% or more, including the substrate material. Depending on the application, it is possible to produce red, and dark colors by adjusting the material characteristics so that only the short wavelength side of the visible light wavelength range, the long wavelength side, or the entire wavelength range is uniformly absorbed [2, 3]. These visible light-transmissive solar cells with visible light transmittance of 80% or less are referred to as semitransparent photovoltaics (STPVs).It is crucial to consider the theoretical limiting efficiency (TLE) for the practical application of TPVs. Recent reports have simulated TLs for single-junction and multi-junction cells with optical absorption in the UV and NIR regions, yet not in the visible region [5]. The results demonstrate that practical conversion efficiencies of 11% and 21% can be obtained for single-junction and 16-junction cells respectively, with 80% visible transmission. The optimal band gap for cells with 100% Vis-EQE (an external quantum efficiency in the visible light range of 435 to 670 nm) is around 1.5 eV, while for cells with 0% Vis-EQE and full transmission in the visible region, the optimal Eg shifts to the lower energy side of 1.1 to 1.2 eV. To use only the UV region without using the NIR region, 2.8 to 3.0 eV or higher can be easily approached with existing technology.Transparent photovoltaic cells (TPVs) and semi-transparent photovoltaic cells (STPVs) developed to date can be broadly classified into the following four types of power generation methods: TPVs (1) Heterojunction and homojunction with 3.0 eV and more wide-gap semiconductors as generating layers [6-8].(2) Glass plate (+ wavelength conversion material) with Si solar cells installed on the end face of the glass plate to form a module [9]. STPVs (3) Increased visible light transmittance by wider-gap semiconductor materials (colored transparent type) [3].(4) SLTPVs [4].If TPV can be made more cost-effective, it can be applied to various applications such as low CO2 emissions in buildings, photovoltaic power generation for agriculture, no external power source required for electric bulletin boards, auxiliary power source for electric vehicles, and so on. Research and development are categorized into the above areas (1) through (4), with (1) through (3) in particular requiring basic research and development from a materials perspective. The number of groups involved in research and requests for practical applications is increasing, and accelerated progress is expected.

The transparent photovoltaic (TPV) device offers onsite power production with greater freedom for integrated applications, in which doping strategy helps to boost device performance. This study explores the effects of gradient doping with titanium (Ti) in zinc oxide (ZnO) to enhance the TPV device performance. By implementing a negative slope in Ti concentration from the substrate to the surface (i.e., reverse‐graded doping), a significant reduction is demonstrated in recombination processes due to the reinforcement in the built‐in electrical field, resulting in an improved photovoltaic efficiency. Additionally, the devices exhibit an average visible transparency value of 68.4% across the 400–825 nm wavelength range, reaching a maximum power conversion efficiency value of 6.74% under 365 nm illumination. These findings underscore the potential of graded Ti‐doping in ZnO to optimize TPV devices for applications in building‐integrated photovoltaics and photo‐communication, contributing to advancements in sustainable energy technologies.

Inspired by the brain, future computation depends on creating a neuromorphic device that is energy-efficient for information processing and capable of sensing and learning. The current computation-chip platform is not capable of self-power and neuromorphic functionality; therefore, a need exists for a new platform that provides both. This Perspective illustrates potential transparent photovoltaics as a platform to achieve scalable, multimodal sensory, self-sustainable neural systems (e.g., visual cortex, nociception, and electronic skin). We present herein a strategy to harvest solar power using a transparent photovoltaic device that provides neuromorphic functionality to implement versatile, sustainable, integrative, and practical applications. The proposed solid-inorganic heterostructure platform is indispensable for achieving a variety of biosensors, sensory systems, neuromorphic computing, and machine learning.

Smart windows can selectively regulate excess solar radiation to reduce heating and cooling energy consumption in the built environment. However, the inevitable dissipation of ultraviolet and near‐infrared into waste heat results in inefficient solar utilization. Herein, a dual‐band selective solar harvesting (SSH) window is developed to realize full‐spectrum utilization. A transparent photovoltaic, converting ultraviolet into electricity, and a transparent solar absorber, converting near‐infrared into thermal energy, are integrated and coupled with a ventilation system to extract heat for indoor use. Compared with common transparent photovoltaics, the SSH window increases solar harvesting efficiency up to threefold while maintaining a considerable visible transmittance. Simulations suggest that the SSH window, besides generating electricity, delivers energy savings by over 30% higher than common smart windows. This is the first integration of transparent photovoltaic and transparent solar absorber into a window, which may open up a new avenue for the development of energy‐efficient buildings.

Role of substrate architecture and modelling on photocurrent and photovoltage in TiO2/NiO transparent photovoltaic

In this paper, the energy harvesting potential from an unmanned aerial vehicle (UAV) wing is discussed. A fixed-wing UAV implemented for surveillance and reconnaissance purposes is investigated in the present work. A piezoelectric patch is embedded into the UAV wingbox, serving as the energy harvesting structure. The structural deformation exerted by a discrete gust load during normal flight condition is utilised as the source of electrical energy. An advanced iterative finite element method (FEM) is applied as the computational tool. The result pointed out that the piezoelectric patch could successfully harvest the energy from the structural vibration.

In this paper, we have presented a MEMS-based piezoelectric fluid-flow based micro energy harvester. The design and modelling of the energy harvester structure was based on a piezoelectric cantilever affixed to a bluff-body. In a cross fluid flow, pressure in the flow channel, in the wake of the bluff body, fluctuates with the same frequency as the pressure variation caused by the Kármán Vortex Street. This fluctuation of pressure in the flow channel causes the piezoelectric cantilever, trailing the bluff-body, to vibrate in a direction normal to the fluid flow direction. COMSOL finite element analysis software are used for the evaluation of various mechanical analysis of the micro energy harvester structure like, physical the Stress and Strain state in the cantilever structures, Eigen frequency Analysis, Transient analysis to demonstrate the feasibility of the design. Detailed steps of modelling and simulation results of the uniform cantilever were explained. The results confirm the probability of the fluid flow based MEMS energy harvester.