Piezoelectric Nanogenerators Based On N-type Zinc Oxide And P-type Spiro-MeOTAD

Zinc oxide is a third-generation direct-bandgap semiconductor with a wurtzite structure,a band gap of 3.37 eV and an exciton binding energy of up to 60 meV.In addition,zinc oxide has many merits such as good biocompatibility and an abundant nano-microstructures.Due to these advantages,zinc oxide has been applied in a variety of electrical,optical and electromechanical devices,such as solar cells,photodetectors,semiconductor light-emitting diodes and the like.At the same time,ZnO's potential of coupling semiconductor properties and piezoelectric properties has been explored in recent years.In 2006,Professor Wang Zhonglin firstly proposed the concept of“nanogenerators”.Since then,various piezoelectric nanogenerators based on zinc oxide nanostructures have been invented.Researchers from all over the world have prepared nanogenerators with various composite structures on all kinds of hard and flexible substrates(sapphire,silicon wafer,fiber,organic film and so on),which convert mechanical energy from human bodys,wind energy,water wave energy into electrical energy,thereby powering various micro-nano electronic devices.Based on two different zinc oxide nanostructures grown on rigid and flexible substrates,two different forms of pn junction-enhanced piezoelectric nanogenerators were prepared through P-type Spiro-MeOTAD organic semiconductor modification.The main research results are as follows:Firstly,zinc oxide nanorods were prepared by magnetron sputtering and low-temperature hydrothermal synthesis on ITO(indium tin oxide)glass and the prepared Spiro-MeOTAD solution was uniformly spin-coated on the zinc oxide nanorods array to form a pn heterojunction.The samples were characterized by scanning electron microscopy(SEM),X-ray diffraction(XRD)and X-ray energy dispersive spectroscopy(EDS).The results show that zinc oxide nanorods have a hexagonal wurtzite structure,which are densely grown and have a good orientation.The Spiro-MeOTAD solution is uniformly spin-coated on the zinc oxide array to form a semi-covered structure with the zinc oxide nanorods.Next,a piezoelectric nanogenerator based on n-type ZnO/p-type Spiro-MeOTAD heterojunction structure was fabricated and its electrical properties were measured by the Keithley 4200 semiconductor characterization system.The results show that the device has a good rectifying characteristic and a strong power-generating performance.Compared with that of conventional nanogenerators based on ZnO nanorods,the power-generating current of the nanogenerator based on n-type ZnO/p-type Spiro-MeOTAD composite structure was improved by 10 times,about 500nA/cm~2.This phenomenon is mainly because that the formed pn junction structure effectively reduces the screening effect inside the zinc oxide nanorods and the parasitic losses at the surface of zinc oxide nanorods.Secondly,we have fabricated a flexible piezoelectric nanogenerator based on n-type ZnO/p-type Spiro-MeOTAD on a ITO-PET substrate.The device was grown by magnetron sputtering and low temperature hydrothermal synthesis method to fabricate nanodisks and spin-coated with Spiro-MeOTAD solution to form pn junction structure.Then the morphology and structure of the nanogenerator were characterized by the same characterization method.The electrical characteristic measurement results show that the output current of the heterojunction-structure flexible nanogenerator can reach300nA/cm~2.The main reason can be explained by the formation of the pn junction structure,which effectively reduces screening effect and flexible substrate effectively increases the number of nanodisks involved in power generation.