The Study Of Ultra-small-sized Nanogenerator For Largely Improved Output

Ultra-small size and large electric output are highly desirable for piezoelectric nanogenerators for powering sensor networks,nanorobotics,and implantable biomedical nanodevices.However,ultra-small size is usually obtained at the expense of output.Therefore,design and subsequent fabrication of high output nanogenerators in ultra-small size are highly desirable,but still challenging.Since the first nanogenerator based on ZnO nanowires has been developed,adoption of ferroelectric materials with high piezoelectric coefficient and integrated design of parallel nanowires have been two effective approaches for enhancing the output of the nanogenerator.From material's point of view,lead zirconate titanate(PZT)is known as a comparable/competent candidate for piezoelectric nanogenerator because of its high piezoelectric coefficient.However,bulk or film PZT is very brittle.Flexible nanogenerator based on PZT nanowires and polymer came along to prevent PZT nanowires from fracture and extend the life cycle.Piezoelectric nanogenerator based on oriented assembly of nanowires is a dominant device developed for converting mechanical energy into electrical energy.By finite element method,the nanogenerator based on oriented assembly of PZT nanowires is modeled to evaluate its capacitance,charge density on the top electrode and open circuit output voltage.Based on different types of PZT materials and polymers,our study presents the output voltage of the nanogenerator by changing of the PZT nanowire's length,diameter,and the nanogenerator's thickness.These results provide an effect guidance for optimizing the output of piezoelectric nanogenerators.Secondly,the output of the piezoelectric nanogenerator based on composite of PZT nanowires and PMMA has been further improved by thoroughly studying of the effect of PZT nanowire's diameter on the output performance of piezoelectric nanogenerators.The peak value of charge density on the top electrode is 19.8 ?C/m2,and the peak value of the open circuit voltage is 3.8 V.The simulation results show that the output performance of piezoelectric nanogenerator is related to PZT's content.With the increase of PZT's content,the output performance of piezoelectric nanogenerator reached the maximum value.Based on the relationship between the PZT's content and the output performance of the piezoelectric nanogenerators,we designed a high-output piezoelectric PZT nanowires/PMMA nanogenerator,which can increase the charge density on the top electrode by 13%,reached 22.4 ?C/m2.At the same time,the open circuit voltage of the piezoelectric nanogenerator increased by 20%,reached 4.56 V.These results can be further used to increase the output of piezoelectric nanogenerators.Thirdly,monolayer MoS2 possesses strong piezoelectric effect,large mechanical stretchability,and advantage of withstanding enormous strains which are essential for generating high power with an ultra-small size.In this work,a rational design of an ultra-small MoS2 nanogenerator with large output is demonstrated by the layer-by-layer assembly of MoS2 monolayers and insulator layers.Using this structure,MoS2 monolayers are integrated in the same orientation,which keeps the advantage of monolayer and simultaneously avoids the influence of the number of atomic layers on the piezoelectric output completely.It can be supposed that an integration of monolayers of MoS2 in the same orientation of adjacent atomic layers will exhibits a larger piezoelectric output;nevertheless,this structure seldom exists in the natural for it is an unstable state.Our design solved this difficult problems.Here,we theoretically demonstrate a proof-of-concept design for nanogenerators with not only ultra-small size,but also high output,taking the benefit from tiny highly efficient functional building blocks based on monolayer MoS2 and their rational integration.We further show that the output performance of the nanogenerator is greatly influenced by the types of insulator materials,thickness of insulator layer,and side length.The large output power generated from an ultra-small size nanogenerator(70 ?m × 70 ?m × 5.2 ?m)reached up to 36 mW when it is mechanically resonant with external pressure and a resistance of 40 k? is loaded.A significantly high conversion efficiency of 71% from mechanical energy to electrical energy can even be achievable when a resistance of 25 k? is loaded.Such an exciting output is already able to directly power nanodevices with the power consumption generally at the level of several milliwatt.Our unique design may open a new door for fabrication of ultra-small and high output nanogenerators.