The Design And Output Enhancement Mechanism Of Hybrid Triboelectric Nanogenerator

As the world enters the era of internet of things?IOTs?and artificial intelligence,microelectronic devices have been developing rapidly towards the trend of more miniaturization,mobility and multi-functionality.Traditional batteries such as the nickel metal hydride battery and lithium battery are no longer suitable to drive the worldwide sensor network that will emerge in the near future.Therefore,to ensure the success of the IOTs,it is very urgent to develop a widely distributed mobile nanoenergy,which can come from solar energy,thermal energy,wind energy or mechanical trigger/vibration.Even though it is not enough to provide consistent power to the main grid,but very suitable for the mobile sensors and self-powered systems.Triboelectric nanogenerator?TENG?is a new type of mechanical energy harvester invented by Wang'group in 2012.It is to use the ubiquitous triboelectrification-induced polarization changes to surface charge as materials'contact-separation varies,thus producing the displacement current that drives electrons to flow between electrodes.In such a working process,the mechanical energy existing in the environment or organisms can be converted into electricity.Due to the wide source of materials,simple preparation,low cost,etc.,TENGs have attracted scientists'extensive and continuous attention around the world,and made great progress in the application fields of micro/nano energy,self-powered sensing,blue energy and high-voltage power supply in recent years.Therefore,it is considered to be the best choice and the most effective approach to realize the distributed and self-powered micro/nano energy.However,the development in practical application of TENG is facing many difficulties.Among them,the lack of output of a single TENG which comes from many factors such as the larger internal resistance of functional materials,unstable mechanical energy source from the environment,working conditions,etc.is the main bottleneck that extremely restricts its commercial development.The previous researches have shown that the output capacity of a TENG is mainly determined by the surface charge density of the friction materials.For this reason,a large number of methods to improve the friction charge density,such as modification of materials,improvement of effective contact area and control of environmental conditions,etc.have been widely investigated.The survey has shown that the environmental energy source collected by TENGs is mainly in the form of mechanical energy,generally involving only one kind of energy conversion mechanism.Therefore,based on the appropriate functional materials,developing the hybrid TENGs that can simultaneously convert multi-energy or realize multi-conversion mechanisms has becoming an important research direction to effectively enhance device's output.In this work,we firstly consider the material's selection and mainly devote to fabricate hybrid TENGs for multi-energy harvesting or multi-mechanism conversion from the combination in three aspects:photoelectric-triboelectric,triboelectric-triboelectric and piezoelectric-triboelectric conversions.For that,the hybrid TENGs can acquire a larger output than that under only one conversion mechanism.In addition,the working principle and the output enhancement mechanism of the fabricated hybrid TENGs are discussed in detail.The content of our paper mainly includes following three parts:Firstly,in order to seek the internal combination of triboelectic-photoelectric on basis of our previous solar cell researches,by employing organic-inorganic lead halide perovskite as the triboelectric layer and light absorber at the same time,the planar TiO₂as electron transport layer?ETL?,ultrathin pentacene as hole transport layer?HTL?,we present a hybrid perovskite-based triboelectric nanogenerator?P-TENG?with a structure of FTO/TiO₂/perovskite/pentacene-PTFE/Al.Based on the coupling of triboelectric and photoelectric conversion mechanisms,P-TENG can simultaneously harvest vibrating energy and solar energy.The experimental results indicate that the significant improvement of output performance under illumination is mainly attributed to the two aspects of reasons:On one hand,a larger number of electron-hole pairs are generated within perovskite upon illumination.Because the introduction of TiO₂ ETL and pentacene HTL distributes an optimized energy-level arrangement in device structure,the photo-induced electrons would be favorably transported away from perovskite to TiO₂,and then FTO.Meanwhile,the photo-induced holes are quickly captured by pentacene.Thus,the more effective charge separation and transfer in perovskite interface lead to a considerable increase of surface charge density of perovskite;On the other hand,the reduction of internal resistance in device is another important source to improve the device output due to the improvement of conductivity in perovskite film under illumination.Secondly,to solve the asynchronism problem on contact-separation process in multi-layer TENG designs.A novel retractable spring-like-electrode multilayer triboelectric nanogenerator?SL-TENG?has been assembled by using spring steel as skeleton and electrode,and PTFE/steel/PET/steel as the repeated unit for harvesting vibration mechanical energy.It has been observed that the output current-time waveform of the device is in good agreement with the standard single-layer device.Experimental results indicates that due to the good elasticity of spring steel and the unique spring structure,the contact-separation synchronism of SL-TENG is greatly improved and further strengthened as frequency increases,which can be used to tandem stack the spring to efficiently convert vibration energy in a small volume,showing a good integration.Thus,the output manyfold increases with the increase of layers.Aside from the enhancement of synchronization,improved roughness,appropriate frequency and amplitude,and increased friction area,it is found that the device's internal resistance decreases gradually with increasing layers maybe one important reason for the performance improvement of multi-layer SL-TENG.Finally,for achieving the more effective mechanical energy conversion in one device structure,based on low-cost and flexible PDMS and PVDF polymer films respectively as triboelectric and piezoelectric function layers,a polymer-based hybrid piezoelectric-triboelectric nanogenerator ?PH-TENG? with Al/PVDF/Cu-PDMS/ITO/PET structure has been demonstrated.The device has realized the simultaneous triboelectric and piezoelectric conversions in the same device structure.In addition,the PDMS and PVDF are further modified by graphene quantum dot?GQD?and TiO₂ nanoparticles respectively,thus,both the device's triboelectric and piezoelectric output are enhanced synchronously.By analyzing the experimental results,we think that the increase of the triboelectric output is due to the improvement of the dielectric properties of PDMS films doped with conductive GQD and the enhancement of the effective contact caused by the change of PDMS surface microstructure,so that more tribo-charges can be accumulated on PDMS surface.While the promotion of the piezoelectric output is mainly attributed to the fact that PVDF film after TiO₂ modification induces and forms more polarized?phases.For these reasons,the improved PH-TENG can convert mechanical energy into electricity more effectively.