Optimum antireflection coatings for heteroface AlGaAs/GaAs solar Cells - Part I: The influence of window layer oxidation

This paper details both the theoretical and experimental results of a modified model for designing MgF2/ZnS double-layer antireflection coatings for AlGaAs/ GaAs heteroface solar cells. The main contribution of the model presented is that it takes into account the possible existence of an oxide layer in the AlGaAs window layer. In a first step the optical behavior of the oxide is modeled and that model is used to recalculate optimal double-layer antireflection coating when a thin AlGaAs oxide layer is present. Significant differences with classical double-layer antireflection coating design are found, such as, the antireflection properties of the oxide layer when formed onto originally thick windows or its equivalent role to that of the ZnS layer (as a high refractive index media) in the coating. Finally, an experimental analysis is carried out to assess empirically the conclusions of the model. These experiments have yielded an excellent agreement with the proposed theory.