The Study Of Output And Mechanism In Novel Metal-Semiconductor Triboelectric Nanogenerator Under Illumination

Triboelectric nanogenerator?TENG?is a new type device that converts all kinds of mechanical energy in the environment into electricity by a conjunction of triboelectrification and electrostatic induction.It can be used as an energy-supplied device for harvesting micro-nano energy and as a self-powered nanosensor.As a new energy technology,TENG has great application potentials in energy harvesting and sensing in the future.Many great progresses have been made in structural design and output efficiency improvement.Among them,harvesting solar energy is an effective way to enhance the performance of the TENG.However,traditional TENG devices use insulating organic polymer and metal as friction materials and they are difficult to directly harvest solar energy.Up till now,some TENGs are connected externally with photoelectric conversion devices such as solar cells to make use of solar energy and increase the output.But these configurations have several problems such as poor matching of two different types of electronic devices,complicated structure and involuted preparation processes.In order to solve problems mentioned above,a single TENG device that can directly make use of mechanical energy and solar energy simutanously to obtain high output efficiency is best choice.In this thesis,we designed and fabricated a simple metal-semiconductor type TENG using semiconductor material with excellent photoelectric properties as a friction layer to realize this concept.1.Firstly,by doping different nano-semiconductor materials in polyvinylidene fluoride?PVDF?matrix:organic-inorganic halide perovskite?CH₃NH₃PbI₃?and organic small molecule semiconductor material?ITCPTC-Se?,two composite films were prepared separately and used as the friction layer of TENG.Next,we measured the outputs of TENG by using composite films at different doping ratios.It was found that doping with 2.5 wt%of CH₃NH₃PbI₃ materials can increase the TENG output performance to some extent,but the output of the devices was unstable.Especially under continuous illumination,the output of devices decreased rapidly.When doped with 0.25 wt%of small molecule material ITCPTC-Se in PVDF matrix,the change in surface crystal grain size and roughness of the composite film resulted in a 0.47 times increase in short-circuit current of the TENG compared to pure PVDF.2.Through the above basic research experiments,a simple metal-semiconductor TENG was designed.The TiO₂ film and the Au film were respectively used as the friction layers to form the Au-TiO₂ type TENG.The Au film served as both the friction layer and the electrode,and the TiO₂ film simultaneously served as another friction layer and light absorbing layer.Under illumination,this simplified TENG increased the short-circuit current by 1.63 times compared to dark state.By further optimizing the device structure,the Au film was sputtered on a flexible polytetrafluoroethylene?PTFE?film instead of a glass substrate,and a semi-flexible Au-TiO₂ type TENG was obtained.Compared with the TENG device using a glass substrate,the output of the device increased the short-circuit current by 2.27 times in dark.In addition,compared with the dark state,this TENG also improved the short-circuit current by 0.48 times under illumination.3.On the basis of the above work,by adjusting the preparation conditions and surface properties of Au film,a new Au-TiO₂ type TENG was preparated.Upon illumination,the current polarity rapidly reversed compared to the dark state.The short-circuit current approximately increased by 5 times.In addition,when TiO₂ and Au film were in close physical contact during the working processes,an obvious photocurrent signal was observed besides the triboelectric signal due to the formation of the metal-semiconductor Schottky contact.By studying the mechanism of generation and transfer of triboelectric charges and photoelectrons,it was found that the surface defect states of TiO₂ under illumination played a decisive role in capturing a large number of photoelectrons and increasing the surface charge density of the friction surface and even reversly increasing the current of TENG.4.Finally,by comparing and analyzing the output performance of different Au-TiO₂ type TENG,it was proved that the work function of Au film leaded to the reversal of electron transfer direction between Au and TiO₂.Therefore,we obtained the Au-TiO₂ type TENG which can increase the output current in the same direction or in the opposite direction,even obtained the Au-TiO₂ type TENG with reduced output under illumination.By controlling the surface properties of the Au and TiO₂ films,the number and polarity of triboelectric charges and photoelectrons on the surfaces can be effectively controlled,thereby regulating the current direction of the TENG.Through further study of the materials,structures and mechanisms of Au-TiO₂type TENG,we not only broaden the material selection range of TENG friction layer and simplify the structure of TENG device,but also obtain a simple independent TENG device which can make use of mechanical energy and solar energy at the same time.Under illumination,the output performance of TENG can be greatly improved.Through the optimization of and device structure and properties of friction films,the output of Au-TiO₂ type TENG can be effectively controlled and regulated.We further deepen our understanding by carefully analyzing the working principle of TENG.Our work further demonstrates and provides a new approach for improving the output in metal-semiconductor TENG.