Analysis of Photonic Crystal Diffraction Grating Based Light Trapping Structure for GaAs Solar Cell

摘要

The paper presents a design and quantitative analysis for an efficient light-trapping structure (LTS) based on Photonic Crystals (PhC) to enhance the performance of thin-film GaAs solar cells. LTS consists of single planar Anti-Reflection coating (ARC) layer at the top assisted by 2D PhC diffraction grating and Distributed Bragg Reflector (DBR) having alternate dielectric layers at the back of the active layer. The structure has been optically analyzed for various absorption layer thicknesses and compared with Lambertian limits, and it has been shown that with optimization of the design carefully, significant enhancement in the cell efficiency will take place for the presented LTS, especially for the devices with very thin absorption layers (typically less than 1000 nm). Further, it is demonstrated that this efficiency enhancement is attributed to the improvement in photon absorption in the wavelength range for which active layer thickness itself is not sufficient for absorption. According to the simulation analysis, the proposed cell efficiency can be enhanced 3.5 times for a 100 nm cell with LTS, and this enhancement shrinks only to 1.5 times for 1500 nm cell. The analysis has shown that for thin cells, the contribution by the optimized LTS is the main reason behind efficiency enhancement whereas the contribution from ARC remains almost constant. The evaluation of the performance of the proposed structure concerning the angle of incident light and fabrication tolerances has also been done, indicating improved performance. The paper also presents the quantitative and comparative analysis of the proposed design with different compatible designs such as a cell having double layer ARC and a cell having pyramidal ARC with PhC as BR design. Their analysis also predicts that the LTS especially BR are more important for thinner active layer cells and the cell with a pyramidal ARC with PhC outperforms the other designs.