Design of sub-wavelength dielectric antireflective grading for multijunction concentrator photovolatics

摘要

In Ⅲ-Ⅴ concentrator applications, sunlight is focused with 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 planar layer ARCs for Ⅲ-Ⅴ multi-junction concentrator cells in case of with/without protective cover glass in conjunction with wide optical aperture angles, a systematic analysis of design parameters and angular dependent antireflective properties of dielectric gratings has been undertaken, through the implementation of sub-wavelength 2D pyramidal gratings of ZnS and TiO_2. The study indicated limited improvement for devices operated with SiO_2 like cover glass. In the absence of SiO_2 like cover glass, the evaluation indicated that reflection-loss related current losses can be reduced by 2-3 fold compared to their double-layer ARC counterparts, i.e. for a 3J metamorphic device this lead to a current improvement of 0.7 mA/cm~2 per concentration for a 60 degree aperture angles.