Broadband enhancement of light harvesting in luminescent solar concentrator

TL;DR

This paper presents a theoretical model showing how nanoscale slot waveguides can significantly enhance light harvesting in luminescent solar concentrators by increasing emission, absorption, and efficiency, enabling near-complete solar photon conversion.

Contribution

The study introduces a Fermi-golden rule-based model for nanoscale LSCs and demonstrates broadband light harvesting enhancement using slot waveguides, surpassing traditional ray-optics approaches.

Findings

Slot waveguides can enhance spontaneous emission via the Purcell effect.

Approximately 80% of solar photons can be converted in the proposed LSC.

The approach enables near-full-spectrum solar photon absorption.

Abstract

Luminescent solar concentrator (LSC) can absorb large-area incident sunlight, then emit luminescence with high quantum efficiency, which finally be collected by a small photovoltaic (PV) system. The light-harvesting area of the PV system is much smaller than that of the LSC system, potentially improving the efficiency and reducing the cost of solar cells. Here, based on Fermi-golden rule, we present a theoretical description of the luminescent process in nanoscale LSCs where the conventional ray-optics model is no longer applicable. As an example calculated with this new model, we demonstrate that a slot waveguide consisting of a nanometer-sized low-index slot region sandwiched by two high-index regions provides a broadband enhancement of light harvesting by the luminescent centers in the slot region. This is because the slot waveguide can (1) greatly enhance the spontaneous emission due to the Purcell effect, (2) dramatically increase the effective absorption cross-section of luminescent centers, and (3) strongly improve the quantum efficiency of luminescent centers. It is found that about 80% solar photons can be ultimately converted to waveguide-coupled luminescent photons even for a low luminescent quantum efficiency of 0.5. This LSC is potential to construct a tandem structure which can absorb nearly full-spectrum solar photons, and also may be of special interest for building integrated nano-PV applications.