Design Optimization of Single-Layer Antireflective Coating for GaAs1−xxPxx/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/Sisubcell. Cells are analyzed for P fractions x = 0, 0.17, 0.29, and 0.37, and ARC materials: Si3N4, SiO2 , ITO, 11fO2, and Al2O3. Optimum ARC thickness ranges from 65-75 nm for Si3N4 and ITO 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/Siabsorber layer thickness is not a strong function of ARC material, but it increases from 250 nm for x = 0 to1 μm for x = 0.29 and 0.37. For all P fractions, Si3N4, 11fO2, and Al2O3 performed almost equally, while SiO2 and ITO resulted in ~1% and ~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 ~1-μm GaAs0.71P0.29 absorber (r = 10 ns): ~26.57% for 75-nm Si3N4 SLARC and 27.62% for 75-nm SiO2/60-nm Si3N4 double-layer ARC.Masdar Institute of Science and Technology (Abu Dhabi, UAE

Study of a 1 eV GaNAsSb photovoltaic cell grown on a silicon substrate

We report the performance of a 1 eV GaNAsSb photovoltaic cell grown on a Si substrate with a SiGe graded buffer grown using molecular beam epitaxy. For comparison, the performance of a similar 1 eV GaN0.018As0.897 Sb 0.085 photovoltaic cell grown on a GaAs substrate was also reported. Both devices were in situ annealed at 700 °C for 5 min, and a significant performance improvement over our previous result was observed. The device on the GaAs substrate showed a low open circuit voltage (VOC) of 0.42 V and a short circuit current density (JSC) of 23.4 mA/cm2 while the device on the Si substrate showed a VOC of 0.39 V and a JSC of 21.3 mA/cm2. Both devices delivered a quantum efficiency of 50%–55% without any anti-reflection coating.Published versio