Piezoelectric Nanogenerators Based On Zinc Oxide Composite Structures

Because of its wide direct band gap of 3.37 e V,whose corresponding wavelength is inthe ultraviolet band,ZnO has obvious advantages in many respects in comparison with other common semiconductors.Firstly,due to its large exciton binding energy of 60 me V,which is higher than the room temperature thermal ionization energy(26 me V),ZnO has broad applications in short wavelength optoelectronic devices under the room temperature or higher temperature.Then,ZnO is more suitable for the high-frequency devices due to its high electron saturation mobility.Moreover,many kinds of piezoelectric devices have been developed utilizing the semiconductor and piezoelectric properties possessed by ZnO which has the advantage of low production cost and simple preparation process.Since the initial study in 2006 by Z.L.Wang’s group,a variety of nanostructured generators on various substrates such as Si,sapphire and fibers have been raised.A variety of methods were developed for converting different types of mechanical energy from nature,organisms and machinery,into electric energy with these nanogenerators.In this paper,based on the ZnO nanostructure,two types of nanogenerator were presented.The main work and result are as follows.We synthesized the vertically aligned ZnO nanorods array by a hydrothermal synthesis technique and the Ba Ti O3 thin layer was coated on the surface of the ZnO nanorods by rf magnetron sputtering process,and the piezoelectric properties were enhanced after annealing and polarization.SEM,XRD and EDS were used to characterize the composite structure.The results showed that ZnO nanorods array densely distributed on the substrate with hexagonal wurtzite structure,and the Ba Ti O3 film uniformly covered on the surface of ZnO nanorods.Then we fabricated a nanogenerator based on the ZnO/Ba Ti O3 composite structure for harvesting energy.Electrical property was measured by a semiconductor characterization system.The nanogenerator has an enhancement output performance with a larger output current of ~ 105 n A than ZnO or Ba Ti O3 based nanogenerator.Moreover,we synthesized another nanogenerator based on ZnO/Ni O composite structure.The transparent nanogenerators were fabricated on indium tin oxide coated(ITO)glass substrate.Then,a thick Ni O layer and ZnO film were sequentially deposited on the substrate by rf magnetron sputtering.A nanogenerator based on the ZnO/Ni O composite structure was fabricated for converting mechanical energy into electricity under external force.By forming a Ni O/ZnO heterostructure,the average output current was up to 70 n A,which areapproximately 10 times larger current density compared to the pristine ZnO nanogenerator.We believe that the amplification is due to the enhancement of the piezopotential via screening effect suppression of the residual free electrons.