Research Of Diffraction Grating And Photonic Crystals In Application Of Solar Cells

This thesis mainly deals with the light absorption of the solar cell, that is, light trapping by the optic al design to increase the solar cells.This article mainly includes following aspects:Using the Legendre polynomial expansion method(LPEM) and Rigorous coupled-wave analysis (RCWA) to conduct simulation calculation of one-dimensional rectangular grating in the visible to near infrared wavelength range of the incident light wave transmittance simulation,find the appropriate duty cycle, grating the depth and thickness of the substrate, so that the transmittance of the grating in the incident angle is within the range of0～60°, the incident wavelength changes within the range of400～1200nm, and its change in the transmittance is relatively stable, the average of which can be reached up to more than96%.Using the plane wave expansion method to calculate the one-dimensional photonic crystals band gap, obtain the conclusion that when the difference of the refractive index of the dielectric material of two cycles becomes greater, the first complete band gap will get wider,on the contrary, it’ll get even narrower. It is good attempt to calculate the band corresponding to the wavelength range which can not be transmitted in the photonic crystal, and produce a back reflection layer of the solar cell with such characteristics of the photonic crystal.In order to improve light absorption the thin-film solar cells, I use the diffraction grating and the one-dimensional photonic crystal structure to increase the solar cells light trapping. I designed a type of reflector that consisted of one-dimensional diffraction gratings and One-dimensional photonic crystal. It can be used for thin-film silicon solar cells. The structure parameters were optimized by Legendre polynomial expansion method, and the reflectivity at the range of400～1200nm was calculated. Under the high reflectivity one-dimensional photonic crystal, the propagation path of the photon can be extended and absorbed in the solar cells. The results show that the diffraction grating and a back reflector in the photonic crystal structure are efficient at the range of750～1100nm. Back-reflection layer can greatly improve the light harvesting capacity and enhance the conversion efficiency of solar cells.Finally, I present a kind of amorphous silicon(a-Si) thin film solar cell structure,which has antireflection coating(AR coating) and back reflector. AR coating consists of four dielectric materials from low to high,back reflector consists of triangle dielectric diffraction grating and one dimensional photonic crystal structure. The parameters of the dielectric layers and the grating have bee n optimized by rigorous coupled wave analysis (RCWA) and plane wave expansion method(PWM) numerical to calculate the reflection efficiency of AR coating and back reflector in0～60°.The results show that AR coating has high transmission in300-750nm and back reflector has high reflection in600-750nm. active layer under TM polarization in700nm a-Si thin film solar cell, I obtain that solar cell has on average95%of absorption after optimizing in range of300-750nm.