  Suppressing the reflection from material interfaces or entire layer stacks
across an extended spectral range is important for various applications. While
many approaches have been described for this purpose, we look at the problem
here from the perspective of helicity preservation. Specifically, the
anti-reflection performance of nano-particle arrays on top of solar cell stacks
is related to two conditions: a high enough degree of discrete rotational
symmetry and the ability of the system to suppress cross-talk between the two
handednesses (helicities) of the electromagnetic field upon light-matter
interaction. For particle-lattice systems with high enough degree of discrete
rotational symmetry ($2\pi/n$ for $n>2$), our numerical studies link the
suppression of backscattering to the ability of the system to avoid the mixing
between the two helicity components of the incident field. In an exemplary
design, we use an array of TiO$_2$ disks placed on top of a flat heterojunction
solar cell stack, and analyze the helicity preservation properties of the
system. We show numerically that a hexagonal array lattice, featuring a higher
degree of discrete rotational symmetry, can improve over the anti-reflection
performance of a square lattice. Importantly, the disks are introduced in an
electrically decoupled manner such that the passivation and electric properties
of the device are not disturbed.
