# Insights into broadband backscattering suppression in solar cells from the helicity preservation point of view

## TL;DR

This paper investigates how helicity preservation in nano-particle arrays can suppress backscattering and improve anti-reflection in solar cells, emphasizing the role of symmetry and helicity cross-talk suppression.

## Contribution

It introduces a helicity-based perspective for backscattering suppression, linking symmetry and helicity preservation to anti-reflection performance in solar cell nanostructures.

## Key findings

- Hexagonal arrays outperform square arrays in anti-reflection.
- High discrete rotational symmetry enhances helicity preservation.
- Electrically decoupled nanoparticle arrays do not disturb solar cell properties.

## Abstract

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.