Optimizing Design of2D Sub-wavelength ARC Gratings for Multijunction III -V Concentrator Cells

摘要

In high X III-V concentrator applications sunlight is focused onto the surface of cell with a wide angular distribution that limits the effectiveness of conventional thin-film AR coatings. Furthermore the transmission properties are generally degraded non-uniformly over the electromagnetic spectrum which in the case of mUlti-junction solar cells leads to additional sub-cell current matching related losses. Here, and in an attempt to identify a better alternative to the conventional dual layer ARCs, we have undertaken a systematic analysis of design parameters and angular dependent anti reflective properties of dielectric grating formed through the implementation of sub-wavelength arrays of 2D pyramidal and hemispherical textures. The study includes evaluation of these properties for several common dielectrics i.e. Si02, Si_3N_4, SiC, TiO_2 and ZnS. The evaluation indicates that through a careful selection of the design and dielectric material these structures can significantly surpass the performance of planar double layer ARCs (i.e. MgF_2/ZnS), and the total number of reflected photons over the 380-2000 nm wavelength range can be reduced to less than 2%. Finally it is shown that the implementation of these structures for a typical 3 or 4 junction solar cells (i.e. inverted metamorphic) and for acceptance angles ranging from 0-60 degrees, reduces total losses of reflected photons for each subcell (and to some extent the resulting current degradation) to less than 4%.