# Optimal trapping of monochromatic light in designed photonic multilayer structures

## TL;DR

This paper presents an optimized multilayer dielectric stack design that significantly enhances local irradiance for photovoltaic upconversion, demonstrating exponential growth with layers and robustness against manufacturing errors.

## Contribution

It introduces a numerically optimized multilayer structure with a proven upper bound, outperforming existing Bragg stacks for photovoltaic applications.

## Key findings

- Irradiance increases exponentially with the number of layers.
- Optimized structures outperform traditional Bragg stacks.
- Manufacturing errors impose a finite limit on enhancement.

## Abstract

We devise an optimised bi-component multi-layered dielectric stack design to enhance the local irradiance for efficient photovoltaic upconversion materials. The field intensity profile throughout the photonic structure is numerically optimized by appropriate tuning of the individual layers' thicknesses. The optimality of the thus inferred structure is demonstrated by comparison with an analytically derived upper bound. The optimized local irradiance is found to increase exponentially with the number of layers, its rate determined by the permittivity ratio of the two material components. Manufacturing errors which induce deviations from the optimised design are accounted for statistically, and set a finite limit to the achievable enhancement. Notwithstanding, realistic assumptions on manufacturing errors still suggest achievable irradiances which are significantly larger than those obtained with the recently proposed Bragg stack structures.