Efficiency Enhancement of GaAs Nano Solar Cell Based on 2D Photonic Crystal Trapping Layer and 2D Index Modulation Layer

In this paper, a nano solar cell structure based on a two-dimensional photonic crystal (2D-PhC) antireflection coating (ARC) trapping layer and a 2D- graded-index (2D-GI) GaAs active layer is presented. These components improve the solar absorption, in-coupling efficiency, quantum efficiency, and optical properties of the active layer. The proposed cell absorption and conversion efficiency were analyzed as a function of the cell layer thickness in comparison with the Lambertian absorption and cell efficiency limits. Additionally, each layer thickness was optimized to enhance the overall solar efficiency. All simulations were conducted in the 300 to 1100 nm range using finite difference time domain (FDTD) analysis, where the 2D-PhC structure was represented by indium tin oxide (ITO) nanorods in an air background. In addition, p-Al(0.85)GaAs/n-Al(0.35)GaAs two-window confinement layers are utilized in contact with the 907-nm GaAs active layer as a perfect match with the 1840-nm ITO-ARC layer to improve the confinement efficiency. Moreover, p-Al(0.85)GaAs/GaAs and GaAs/n-Al(0.35)GaAs 2D-GI active layer structures are used for index modulation to enhance the active layer properties and increase the cell short-circuit current. The main objective of this study is to determine the optimum design of a solar cell that can provide the highest power conversion efficiency using inexpensive semiconductor materials. One of the expected results from this research is the design of a 100- $\mu \text{m}^{2}$ nano solar cell with 39.2% conversion efficiency, a short circuit current density of 44.38 mA/cm², and an open-circuit voltage of 1 V.