Photocurrent Enhancement Of Graphene Photodetectors Based On Mie Scattering And Other Applications Of Mie Scattering

Graphene has a unique band structure, the ultrafast election transfer rate, the excellent physical and chemical properties. So it has became an important two-dimensional material for new type of photodetectors. But the separation rate of the carriers is still low because it is difficult to for a heterojunction for graphene. In this thesis, a new type of graphene photodetectors based on Mie scattering has been prepared to improve the light absorption rate, the carrier separation and detection sensitivity of the graphene photodetectors. At the same time, the research of the optical absorption of solar cell is another application of Mie scattering. The main work is as follows:1.FDTD simulation software was used to design a new type of graphene photodetector based on Mie scattering. The influence of the microspheres on the optical field distribution was studied by changing the the materials, size, laser wavelength and other parameters. It is found that the Mie scattering microspheres can regulate the optical field obviously and can result in the nonequilibrium optical field potential difference in the detector.2. The graphene photodetectors based on Mie scattering were prepared with the large area graphene grown by CVD. The electrodes were prepared by microfabrication technology. The microspheres were dispersed in the liquid and placed between the electrodes on graphene. Experimental results show that by using Mie scattering microspheres, the photocurrent of the graphene photodetectors increased 300%. It shown that light field potential difference caused by the Mie scattering structure can improve the charge separation efficiency and increase the photocurrent.3. The spherical hierarchical structure film has been fabricated by TiO2 nanoparticles. It can enhance the light absorption based on Mie scattering and has a large specific surface area. So it is an appropriate structure for dye-sensitized solar cells(DSSCs). In this thesis, the nanostructures tune of TiO2 hierarchical sphere is experimentally studied for DSSCs application. By altering sintering temperatures, the contact area between adjacent nanoparticles within hierarchical spheres is adjusted. The optimal contact area is found to correspond to sintering temperature of about 450℃. The DSSC’s efficiency is at least 12.3% increasing compared with the other conditions when the sintering temperature is 450℃.