FDTD Simulation Of Optical Antenna For Photovoltaic Devices

Photovoltaics, the conversion of sunlight to electricity, could make a considerablecontribution to solving the energy problem that our society faces in the next generation.Because of its low cost, there is great interest in thin-film solar cell. A limitation in allthin-film solar-cell technologies is that the absorbance of light is small. Therefore,structuring the thin-film solar cell so that light is trapped inside to increase the absorbanceis very important. Optical nano-antenna has local field enhancement effect. This effectclosely related to the surface plasmon. In this dissertation we investigate the suitability oflocalized surface plasmon on silver nanoparticles for enhancing the absorbance of siliconsolar cells utilizing finite-difference time-domain (FDTD) method. The main researchcontents are as follows:Firstly, this dissertation introduces the traditional antenna theory, the opticalproperties of metals, and optical nano-antennas. When the frequency of theelectromagnetic wave is not within too high optical frequency range, we only consider thefree electron influences on metallic dielectric function and using Drude model to describethe free electron. When the frequency of the electromagnetic wave is greater than thethreshold of electronic interband transition, electronic interband transition occurs, then weuse Lorentz model to remedy this shortage.Secondly, the differential form of Maxwell equations is discretized for the numericalsimulation by FDTD method. We also analyse its numerical dispersion and stability andyield the requirements of the space and the time interval of numerical dispersion. Thisdissertation also introduces the absorbing boundry condition at truncated boundry and theapproach of importing incident wave——total/scattering field method in limited FDTDregion.Finally, the parameters of Ag nanoparticle and monocrystalline silicon can beobtained by using least square method and the complex refractive index of the twomaterials. Subsequently, this dissertation investigates the influences of cylindrical andsemi-cylindrical metal nanoparticle array on the electromagnetic wave absorptivity ofmonocrystalline silicon in solar cells at various wavelengths. The results show that nanooptical antenna can indeed increase the electromagnetic wave absorptivity of monocrystalline silicon in solar cells over a certain spectral range, and this is a novelapproach to get light trapping for silicon solar cells. And the enhancement of theabsorptivity is connected with the geometry, radius and the wavelength of incident wave.These have some guiding significance for enhancing the properties of solar cells.