Influence of double- and triple-layer antireflection coatings on the formation of photocurrents in multijunction III–V solar cells

The results of simulation by the transfer-matrix method of TiO$_{2}$/SiO$_{2}$ double-layer and TiO$_{2}$/Si$_{3}$N$_{4}$/SiO$_{2}$ triple-layer antireflection coatings for multijunction InGaP/GaAs/Ge heterostructure solar cells are presented. The TiO$_{2}$/SiO$_{2}$ double-layer antireflection coating is experimentally developed and optimized. The experimental spectral dependences of the external quantum yield of the InGaP/GaAs/Ge heterostructure solar cell and optical characteristics of antireflection coatings, obtained in the simulation, are used to determine the photogenerated current densities of each subcell in the InGaP/GaAs/Ge solar cell under AM1.5D irradiation conditions (1000 W/m$^2$) and for the case of zero reflection loss. It is shown in the simulation that the optimized TiO$_{2}$/Si$_{3}$N$_{4}$/SiO$_{2}$ triple-layer antireflection coating provides a 2.3 mA/cm$^2$ gain in the photocurrent density for the Ge subcell under AM1.5D conditions in comparison with the TiO$_{2}$/SiO$_{2}$ double-layer antireflection coating under consideration. This thereby provides an increase in the fill factor of the current–voltage curve and in the output electric power of the multijunction solar cell.