Large scale synthesis of carbon dots for efficient luminescent solar concentrators

Abstract

Luminescent solar concentrators (LSCs) are large-area sunlight collectors, and they are able to reduce the cost of electricity and are suitable for application in building integrated photovoltaics. The key factor determining the optical efficiency of the LSC is the optical properties of the fluorophores. Among various types of fluorophores, carbon quantum dots (C-dots) have attracted great attention because of their size/shape/composition dependent optical properties and high stability. Although LSCs based on C-dots have been reported recently, it is still a big challenge to produce highly-bright cost-effective C-dots on a large-scale via a simple approach for efficient LSC fabrication. In this work, we demonstrate a simple solvent-free heating method using metal salts as dehydrating agents to produce C-dots in a large-quantity (100 gram per batch). The as-prepared C-dots have a typical absorption ranging from 300 to 500 nm, a large Stokes shift of 0.73 eV, a quantum yield (QY) as high as 70% and a small absorption/emission spectral overlap. The metal cation can not only contribute to the dehydration of the precursors, but also cap the C-dot surface by forming a stable structure, leading to a strong absorption peak at 405 nm and a large Stokes shift because of the intermediate energy states. Compared to Cu, Fe, Mg, Al, and Sr cations, Ca²⁺/Ba²⁺ capped C-dots exhibited the highest QY because of the efficient surface passivation. As a proof-of-concept, we fabricated the laminated LSCs using the as-obtained C-dots as fluorophores. The optimized LSC based on C-dots produced using BaCl₂ or CaCl₂ exhibits an external optical efficiency as high as 3.2% with a lateral size of 100 cm². These results indicate that the solvent-free heating method can provide high-quality C-dots as building blocks for potential LSC applications.