Transparent Triboelectric Nanogenerator Research Articles

Self-powered electronic paper with energy supplies and information inputs solely from mechanical motions

The electronic paper (E-paper) displays features such as flexibility, sunlight visibility, and low power consumption, which makes it ideal for Internet of Things (IoT) applications where the goal is to eliminate bulky power modules. Here, we report a unique self-powered E-paper (SPEP), where information inputs and energy supplies are all converted from mechanical motion by a triboelectric nanogenerator (TENG). The operation of an electrophoretic E-paper is first investigated, identifying the current density as a determinative parameter for driving pigment particle motion and color change. Electrical and optical responses of the E-paper driven by a sliding-mode TENG are then found to be consistent with that under a current source mode. All-in-one monochromic and chromatic SPEPs integrated with a flexible transparent TENG are finally demonstrated, and a pixelated SPEP is discussed for future research. The sliding-driven mechanism of SPEP allows for a potential handwriting function, is free of an extra power supply, and promises undoubtedly a wide range of future applications.

Super Tough and Self-Healable Poly(dimethylsiloxane) Elastomer via Hydrogen Bonding Association and Its Applications as Triboelectric Nanogenerators.

Poly(dimethylsiloxane) (PDMS) as one of the electron-drawing materials has been widely used in triboelectric nanogenerators (TENG), which is expected to generate electron through friction and required to endure dynamic loads. However, the nature of the siloxane bond and the low interchain interaction between the methyl side groups result in low fracture energy in PDMS elastomers. Here, a strategy that combined the advantages of the dynamic of hierarchical hydrogen bonding and phase-separation-like structure was adopted to improve the toughness of PDMS elastomers. By varying both stronger and weaker hydrogen bonding within the PDMS network, a series of super tough (up to 24,000 J/m2), notch-insensitive, transparent, and autonomous self-healable elastomers were achieved. In addition, a hydrophilic polymeric material (PDMAS-U10) was synthesized as the conductive layer. A transparent TENG was fabricated by sandwiching the PDMAS-U10 between two pieces of the PDMS elastomer. Despite its hydrophilic nature, PDMAS-U10 exhibit strong adhesion interaction with hydrophobic PDMS elastomers. As such, a tough (16,500 J/m2), self-healable (efficiency ∼97%), and transparent triboelectric nanogenerator was constructed. A self-powered system employing the TENG is also demonstrated in this work.

Enhancing the Performance of a Stretchable and Transparent Triboelectric Nanogenerator by Optimizing the Hydrogel Ionic Electrode Property.

Triboelectric nanogenerators (TENGs) with high transparency and stretchability are desired for invisible and adaptable energy harvesting and sensing. Hydrogel-based TENGs (H-TENG) have shown promising attributes toward flexible and transparent devices. However, the effect of hydrogel property on the triboelectric performance of H-TENG is rarely investigated. Herein, dual-network hydrogels composed of dual-cross-linked poly(vinyl alcohol) (PVA) and sodium alginate (SA) were synthesized and used as ionic electrodes in H-TENGs. The elasticity of the hydrogel was controlled by varying the concentration of SA, and the distinct influence of hydrogel viscoelastic property on H-TENG performance was verified for the first time. By tuning the conductivity and viscoelasticity of PVA/SA hydrogel, theoptimum H-TENG exhibitedhigh transparency (over 90%) and stretchability (over 250%) and peak output voltage and current of 203.4 V and 17.6 μA, respectively. A specially designed polydimethylsiloxane (PDMS) bag effectively prevents hydrogel dehydration and maintains a stable output in continuous operation. The H-TENG achieved a power density of 0.98 W/m2 on a 4.7 MΩ external resistor. The H-TENG could easily light 240 green and blue LEDs simultaneously and demonstrated capability to power small electronics, such as a digital timer and pedometer. This study provides insights into the influence of hydrogel property on H-TENG performance and gives guidance for designing and fabricating highly stretchable and transparent TENGs.

A flexible self-charged power panel for harvesting and storing solar and mechanical energy

A flexible self-charged power panel is integrally designed and fabricated to simultaneously harvest solar and mechanical energy and convert and store in electric energy. The flexible amorphous silicon solar cell, the transparent triboelectric nanogenerator (TENG), and lithium (Li)-ion batteries are coherently integrated into one thin panel with the encapsulating materials, ethylene-tetra-fluoro-ethylene (ETFE) for the solar modules. The flexible self-charged power panel exhibits good performance to directly convert solar and mechanical energy into electricity that was directly stored in Li-ion battery without excessive energy loss. The integrated device also greatly minimizes the usage of current collectors, substrates and packaging materials. Moreover, such a power panel can compensate for the absence of solar cells and prolongs the time of energy supply and improve the energy density of the whole device.

Highly transparent triboelectric nanogenerator utilizing in-situ chemically welded silver nanowire network as electrode for mechanical energy harvesting and body motion monitoring

Triboelectric nanogenerators (TENGs) functioning as energy harvester as well as body motion sensor pose great significance for oncoming wearable (opto)electronic systems. Herein, A transparent welded AgNW electrode based TENG (WA-TENG) is demonstrated. AgNWs are in-situ chemically welded with surfacial silver oxide naturally formed in air as solder and hydrazine as reductant based on epitaxial recrystallization, ensuring high transparency and conductivity of the electrode used in TENG. This welding endows AgNW electrodes with a high transmittance of 96% (at 77 Ω/sq sheet resistance) and low sheet resistance of 18 Ω/sq (at 92% transmittance), meanwhile, can effectively heal the damaged AgNW network. The WA-TENG exhibits a transmittance up to 95%, and generates an open-circuit voltage (Voc) of 66 V, short-circuit current (Isc) of 8.6 μA, and peak power density of 446 mW/m2 under single-electrode mode at 2 Hz. Besides, it can be employed to monitor human body motions, including bending of the elbow, eye blinking, and bending angle and frequency of the finger. Lastly, the WA-TENG serves as a tactile sensor to record touch control of a smart phone by the finger. The WA-TENG with standout transparency, electric output and sensing performance underscores the crucial role in self-powered wearable multifunctional devices.

Remarkably enhanced triboelectric nanogenerator based on flexible and transparent monolayer titania nanocomposite

Triboelectric nanogenerator (TENG) is an effective way to convert mechanical energy into electricity, which has been approved as new types of energy harvesting and strain sensor technology. In this study, we design and fabricate a flexible and transparent TENG based on a nanocomposite film made of PVDF and titania monolayer (TOML). The PVDF/TOML composite TENG with 1.5 wt% TOML generates output signals of 52.8 V and 5.69 μA/cm2 and a 50-fold enhancement in output power, compared to the pure PVDF-based TENG. It is found that the synergy between efficient electron capture and high dielectric constant of TOML leads to enhancing the performance of the TENG. Besides, the nanocomposite maintains high performance of the stability and durability due to the excellent compatibility between the inorganic TOML and organic PVDF.

(Invited) Flexible Triboelectric Nanogenerator and Highly Sensitive Pressure Sensor

Transparent electronic devices built on flexible substrates are expected to meet emerging technological demands for the next generation of flexible electronic and optoelectronic devices. A suitable energy source is a vital part for realizing fully self-powered systems. Energy harvesting and conversion technology from environment in which the system will be deployed is a promising route. Recently, we have introduced a new concept on the basis of triboelectrification and electrostatic induction for successfully converting mechanical energy into electric energy at an energy conversion efficiency as high as 50%. Subsequently, transparent triboelectric nanogenerators (TENGs) using indium tin oxide (ITO) or graphene as electrodes have been demonstrated, which are the only possible power source that light can penetrate through. However, there is a need for a low-cost and large area compatible technology for producing transparent TENGs with high-output power supply, aiming for applications such as touch screens. In our previous work, we fabricated a transparent TENG and pressure sensor by using polyester (PET) and polydimethylsiloxane (PDMS) films as flexible substrates to integrate ITO electrodes. It has also been demonstrated that the patterned surface is an effective method to improve the output performance of the TENG. However, realizing such a structure is not trivial in mass production and the patterned structure will reduce the transparency of the device due to the light scattering effect. Here, we present a simple, cost-effective and large-scalable method for fabrication of highly transparent TENGs. Although triboelectric effect has been known for thousands years, the underlying mechanism is actually very complex and still under debating. The competing possible mechanisms appear to include electron transfer, ion transfer, bond dissociation, chemical changes, and material transfer, and it is likely that different mechanisms may be involved depending on the specific materials and environmental conditions. Usually, it needs specialized equipment to characterize the charged surface and study the mechanism. It is worth noting that the output performance of TENG can directly reflect the capacity of the triboelectrification. Herein, we use this feature to investigate the mechanism of the triboelectrification by examining various factors on the performance of TENG. Furthermore, another meaningful outcome of our study is that we explore the mechanism from the microscopic and molecular perspective using the methods for surface characterization, which would be beneficial to the improvementand application of TENG at a large scale. References F. R. Fan, Z. Q. Tian, Z. L. Wang, Nano Energy 2012, 1, 328-334. F. R. Fan, L. Lin, G. Zhu, W. Z. Wu, R. Zhang, Z. L. Wang, Nano Lett. 2012, 12, 3109-3114. F. R. Fan, J. J. Luo, W. Tang, C. Y. Li, C. P. Zhang, Z. Q. Tian, Z. L. Wang, J. Mater. Chem. A 2014, 2, 13219-13225.

Transparent-flexible-multimodal triboelectric nanogenerators for mechanical energy harvesting and self-powered sensor applications

Triboelectric nanogenerators (TENGs) harvest and convert mechanical energy to electrical energy. TENGs that are transparent and flexible can be applied to various (opto-)electronic devices supporting finger- or pen-based touchscreen inputs. This paper presents a transparent, flexible TENG that harvests mechanical tapping energy (typically discarded) by simple placement on touchscreen devices. The developed TENG consists of flexible and transparent conducting electrodes (FTCE) with high transmittance (> 93%) and low sheet resistance (18.5 Ω/sq), and transparent 3D-hierarchical polydimethylsiloxane (PDMS) with porous pyramid-patterns. In this study, the developed TENG directly powered eight light-emitting diodes (LEDs) by harvesting the mechanical energy produced by tapping with a touch pen while playing a smartphone game. We also used the transparent TENG as a transparent single-electrode-based, self-powered raindrop detection sensor on a window for a smart home. Our results indicate that the proposed TENG can be used not only as an effective mechanical energy harvester for transparent, flexible, and next-generation optoelectronics devices but also as a self-powered sensor for future Internet-of-Things applications.

Nature Degradable, Flexible, and Transparent Conductive Substrates from Green and Earth-Abundant Materials

The rapid development of wearable and disposable electronic devices and the rising awareness of environmental sustainability impose growing new demands on the nature degradability of current electronic and energy systems. Here we report a new type of flexible transparent conductive paper completely made from green and earth abundant materials which are also fully degradable and recyclable. Aluminum-doped zinc oxide (AZO) was deposited by low-temperature atomic layer deposition (ALD) as the transparent conductive oxide (TCO) layer on transparent cellulose nanofibril (CNF) papers. The mesoporous structure of the CNF paper rendered strong adhesion of the AZO layer and exhibited excellent mechanical integrity and electrical conductivity within a wide range of tensile and compressive strains. The AZO-CNF paper could be completely dissolved in warm city water after one-hour stirring, demonstrating an excellent nature degradability. A flexible and transparent triboelectric nanogenerator (TENG) was further fabricated using such AZO-CNF papers with a performance that was comparable to other synthetic polymer-based systems. This work illustrated a new and promising strategy of utilizing 100% green and degradable materials in novel electronic and energy harvesting devices.

Ultrastretchable, transparent triboelectric nanogenerator as electronic skin for biomechanical energy harvesting and tactile sensing.

Rapid advancements in stretchable and multifunctional electronics impose the challenge on corresponding power devices that they should have comparable stretchability and functionality. We report a soft skin-like triboelectric nanogenerator (STENG) that enables both biomechanical energy harvesting and tactile sensing by hybridizing elastomer and ionic hydrogel as the electrification layer and electrode, respectively. For the first time, ultrahigh stretchability (uniaxial strain, 1160%) and transparency (average transmittance, 96.2% for visible light) are achieved simultaneously for an energy-harvesting device. The soft TENG is capable of outputting alternative electricity with an instantaneous peak power density of 35 mW m-2 and driving wearable electronics (for example, an electronic watch) with energy converted from human motions, whereas the STENG is pressure-sensitive, enabling its application as artificial electronic skin for touch/pressure perception. Our work provides new opportunities for multifunctional power sources and potential applications in soft/wearable electronics.

Controlled fabrication of nanoscale wrinkle structure by fluorocarbon plasma for highly transparent triboelectric nanogenerator

In this paper, we report a novel nanoscale wrinkle-structure fabrication process using fluorocarbon plasma on poly(dimethylsiloxane) (PDMS) and Solaris membranes. Wrinkles with wavelengths of hundreds of nanometers were obtained on these two materials, showing that the fabrication process was universally applicable. By varying the plasma-treating time, the wavelength of the wrinkle structure could be controlled. Highly transparent membranes with wrinkle patterns were obtained when the plasma-treating time was <125 s. The transmittances of these membranes were >90% in the visible region, making it difficult to distinguish them from a flat membrane. The deposited fluorocarbon polymer also dramatically reduced the surface energy, which allowed us to replicate the wrinkle pattern with high precision onto other membranes without any surfactant coating. The combined advantages of high electron affinity and high transparency enabled the fabricated membrane to improve the performance of a triboelectric nanogenerator. This nanoscale, single-step, and universal wrinkle-pattern fabrication process, with the functionality of high transparency and ultra-low surface energy, shows an attractive potential for future applications in micro- and nanodevices, especially in transparent energy harvesters.

A leaf-molded transparent triboelectric nanogenerator for smart multifunctional applications

Transparent, flexible and highly efficient portable power sources are essential components of the next generation electronics and optoelectronic devices. However, complicated technology, expensive cost, environmental pollution and low-efficient output have limited its development. Herein, based on periodic contact/separation between human skin and the microstructured polydimethylsiloxane (PDMS) film, we demonstrate a transparent flexible triboelectric nanogenerator (TENG) through a relatively simple, low-cost, environmental-friendly and high-efficient method. For the first time, the natural leaves with rich surface textures were introduced to make microstructures on PDMS films as effective friction surface in the TENG. Furthermore, long silver nanowires (200µm in length at least) through novel synthesis were assembled as high-performance electrode, resulting in the entirely flexible and transparent TENG. Owing to the unique design, the transparent flexible TENG was eventually obtained with an enhanced output (Voc=56V; Isc=3.1μA) and remarkable transparency (88%).Owing to compelling features of the TENG, a self-powered user-interactive wearable system was successfully established by integrating a flexible electrochromic device (ECD). The remarkable color-tunable ability via mechanical control of our system, highly inspired by chameleons, is potentially useful in military camouflage, monitoring human activity visually, as well as replacing performance of face change in Sichuan Opera. Therefore, this research is a substantial advancement toward the construction of transparent nanogenerator and its multifunctional applications in energy conversation, wearable electronics, healthcare, culture experience, and even environmental protection.

Hybrid Energy Cell with Hierarchical Nano/Micro-Architectured Polymer Film to Harvest Mechanical, Solar, and Wind Energies Individually/Simultaneously.

We report the creation of hybrid energy cells based on hierarchical nano/micro-architectured polydimethylsiloxane (HNMA-PDMS) films with multifunctionality to simultaneously harvest mechanical, solar, and wind energies. These films consist of nano/micro dual-scale architectures (i.e., nanonipples on inverted micropyramidal arrays) on the PDMS surface. The HNMA-PDMS is replicable by facile and cost-effective soft imprint lithography using a nanoporous anodic alumina oxide film formed on the micropyramidal-structured silicon substrate. The HNMA-PDMS film plays multifunctional roles as a triboelectric layer in nanogenerators and an antireflection layer for dye-sensitized solar cells (DSSCs), as well as a self-cleaning surface. This film is employed in triboelectric nanogenerator (TENG) devices, fabricated by laminating it on indium-tin oxide-coated polyethylene terephthalate (ITO/PET) as a bottom electrode. The large effective contact area that emerged from the densely packed hierarchical nano/micro-architectures of the PDMS film leads to the enhancement of TENG device performance. Moreover, the HNMA-PDMS/ITO/PET, with a high transmittance of >90%, also results in highly transparent TENG devices. By placing the HNMA-PDMS/ITO/PET, where the ITO/PET is coated with zinc oxide nanowires, as the top glass substrate of DSSCs, the device is able to add the functionality of TENG devices, thus creating a hybrid energy cell. The hybrid energy cell can successfully convert mechanical, solar, and wind energies into electricity, simultaneously or independently. To specify the device performance, the effects of external pushing frequency and load resistance on the output of TENG devices are also analyzed, including the photovoltaic performance of the hybrid energy cells.

Flexible and transparent triboelectric nanogenerator based on high performance well-ordered porous PDMS dielectric film

A flexible and transparent triboelectric nanogenerator (FT-TENG) has great potential for application in self-powered biosensor systems, electronic skin and wearable electronic devices. However, improving the output performance with little damage to its optical properties is challenging. Herein, we have developed an FT-TENG that has a well-ordered nest-like porous polydimethylsiloxane (NP-PDMS) film and graphene transparent electrodes. The NP-PDMS film with ordered pores is fabricated by hydrochloric acid etching of 500 nm sized ZnO spheres made of aggregated nanoparticles, having a light transmittance of 81.8% and a water contact angle of 118.62°. The FT-TENG based on the NP-PDMS film with a porosity of 12%, gives a maximum output of 271 V and 7.8 μA, which are respectively, 3.7 and 2.1-fold of those of a TENG with a flat PDMS film. The peak output power reaches 0.39 mW with a load resistance of 9.01 MΩ. The dielectric constant and effective thickness of the NP-PDMS film and the capacitance and charge transfer of the FT-TENG are systematically investigated. This work provides a novel and effective method to enhance the performance of FT-TENGs with little damage to their optical properties.

Integrated multi-unit transparent triboelectric nanogenerator harvesting rain power for driving electronics

Transparent and high efficient power sources harvesting energy from ambient environment is a desirable solution to on-site energy demand for organic electronic and optoelectronic devices. Here we report an integrated multi-unit transparent triboelectric nanogenerator (MT-TENG) for harvesting clean energy from ambient water motions. The instantaneous output power density reaches 27.86mW/m2, which is 11.6 times of that generated from individual T-TENG with the same working dimension. The output of the MT-TENG can be further enhanced by miniaturizing the size of each single unit. In addition, the rational design of the MT-TENG increases the safety for future practical applications. The influence of temperature and pH value of water on the electric outputs is also systematically studied in consideration of different application environment. Given the compelling features, such as, high efficiency, cost-effective, easily implemented, it has great potential of integrating with building, vehicle or silicon-based solar cell to harvest clean energy from raindrop for powering electronics and constructing smart systems.

(Invited) Mechanical Energy Harvesting Using Triboelectric/Piezoelectric Properties from Two-Dimensional Materials

Graphene has not been used as an active material in energy harvesting devices and systems. Recently, a new type of power-generating device that converts mechanical energy into electricity using triboelectricity was intensively studied. The triboelectric effect depends on various factors, such as the electron affinity, work function, friction, chemical structure, pressure, surface roughness, and humidity. A number of theoretical studies on the electrostatic behavior of graphene have been reported, and it has been concluded that graphene can store an electric charge for a period of time, which adds to its suitability for triboelectric nanogenerators. We designed and fabricated flexible transparent triboelectric nanogenerators by using monolayer, bilayer, trilayer, and quadlayer graphene. The dependence of the power output performance of the graphene triboelectric nanogenerators on the number of graphene layers is also discussed in detail in terms of the work function and friction, which arises due to different electronic relations between randomly and regularly stacked graphene layers. Furthermore, this talk will introduce a direct observation of the directional dependent piezoelectric effect in CVD grown monolayer MoS2 using lateral piezoresponse force microscopy measurements and the piezoelectric power output from piezoelectric nanogenerators fabricated with monolayer MoS2.

Roll-to-Roll Green Transfer of CVD Graphene onto Plastic for a Transparent and Flexible Triboelectric Nanogenerator.

A novel roll-to-roll, etching-free, clean transfer of CVD-grown graphene from copper to plastic using surface-energy-assisted delamination in hot deionized water is reported. The delamination process is realized by water penetration between the hydrophobic graphene and a hydrophilic native oxide layer on a copper foil.The transferred graphene on plastic is used as a high-output flexible and transparent triboelectric nanogenerator.

Self-Powered Electrochromic Smart Window Driven By Transparent Triboelectric Nanogenerators Via Harvesting Wind and Rain Energies

Self-powered system is one of promising electronic concepts in upcoming future due to its independent and sustainable operations without a battery. To realize this idea, triboelectric nanogenerator (TENG) was recently invented that could effectively convert the ambient mechanical energy into electricity to power up portable electronics. In this work, the concept of self-powered smart window system was realized through integrating an electrochromic device (ECD) with a transparent TENG driven by wind blowing and raindrops The ECD consisted of Prussian blue and zinc hexacyanoferrate as the electrochromic material and the ion storage layer, respectively. Driven by the sustainable output of the TENG, the optical properties, especially the transmittance of the ECD displays reversible variations due to electrochemical redox reactions. The maximum transmittance change can reach up to 32.4% at 695 nm which is comparable to that operated by conventional electrochemical potentialstation (32.5%). This research is a substantial advancement towards the practical application of nanogenerators and self-powered systems, and it paves the way for the development of fully independent smart windows or high-performance displays.

Motion-Driven Electrochromic Reactions for Self-Powered Smart Window System

The self-powered system is a promising concept for wireless networks due to its independent and sustainable operations without an external power source. To realize this idea, the triboelectric nanogenerator (TENG) was recently invented, which can effectively convert ambient mechanical energy into electricity to power up portable electronics. In this work, a self-powered smart window system was realized through integrating an electrochromic device (ECD) with a transparent TENG driven by blowing wind and raindrops. Driven by the sustainable output of the TENG, the optical properties, especially the transmittance of the ECD, display reversible variations due to electrochemical redox reactions. The maximum transmittance change at 695 nm can be reached up to 32.4%, which is comparable to that operated by a conventional electrochemical potentiostat (32.6%). This research is a substantial advancement toward the practical application of nanogenerators and self-powered systems.

Highly transparent triboelectric nanogenerator for harvesting water-related energy reinforced by antireflection coating.

Water-related energy is an inexhaustible and renewable energy resource in our environment, which has huge amount of energy and is not largely dictated by daytime and sunlight. The transparent characteristic plays a key role in practical applications for some devices designed for harvesting water-related energy. In this paper, a highly transparent triboelectric nanogenerator (T-TENG) was designed to harvest the electrostatic energy from flowing water. The instantaneous output power density of the T-TENG is 11.56 mW/m2. Moreover, with the PTFE film acting as an antireflection coating, the maximum transmittance of the fabricated T-TENG is 87.4%, which is larger than that of individual glass substrate. The T-TENG can be integrated with silicon-based solar cell, building glass and car glass, which demonstrates its potential applications for harvesting waste water energy in our living environment and on smart home system and smart car system.