Design Optimization of Single-Layer Antireflective Coating for GaAs1-xPx/Si Tandem Cells With x=0, 0.17, 0.29, and 0.37

Single-layer antireflective coating (SLARC) materials and design for GaAs1-xPx/Si tandem cells were analyzed by TCAD simulation. We have shown that optimum SLARC thickness is a function of bandgap, thickness, and material quality of top GaAs1-xPx subcell. Cells are analyzed for P fractions x = 0, 0.17, 0.29, and 0.37, and ARC materials: Si3N4, SiO2, ITO, HfO2, and Al2O3. Optimum ARC thickness ranges from 65-75 nm for Si3N4 and ITO to similar to 100-110 nm for SiO2. Optimum ARC thickness increases with increasing GaAs1-xPx absorber layer thickness and with decreasing P fraction x. Simulations show that optimum GaAs1-xPx absorber layer thickness is not a strong function of ARC material, but it increases from 250 nm for x = 0 to similar to 1 mu m for x = 0.29 and 0.37. For all P fractions, Si3N4, HfO2, and Al2O3 performed almost equally, while SiO2 and ITO resulted in similar to 1% and similar to 2% lower efficiency, respectively. Optimum SLARC thickness increases as the material quality of the top cell increases. The effect of ARC material decreases with decreasing GaAs1-xPx material quality. The maximum efficiencies are achieved for cells with similar to 1-mu m GaAs0.71P0.29 absorber (tau = 10 ns): similar to 26.57% for 75-nm Si3N4 SLARC and 27.62% for 75-nm SiO2/60-nm Si3N4 double-layer ARC.