Luminescent solar concentrators based on plasma-synthesized silicon quantum dots

Abstract

Luminescent solar concentrators (LSCs) are large, flat waveguides doped or coated with fluorophores. These fluorophores re-emit luminescence from absorbed sunlight and their luminescence is guided to peripheral or surface-mounted solar cells. LSCs are promising for electrode-less photovoltaic windows in urban buildings and for greenhouse roof panels in agricultural farming because they can simultaneously produce clean electricity while transmitting sunlight. In this work, LSCs based on plasma-synthesized silicon quantum dots (Si QDs) are developed both experimentally and analytically, and the feasibility of LSC application in agriculture is investigated. Single-layer Si QD-poly(methyl methacrylate) (PMMA) thin film LSCs with different Si QD concentrations are fabricated to study the Si QD concentration limitation in PMMA films. Considering the limitation of Si QD concentration and Si QDs’ incomplete use of the available solar spectrum, the first bilayer LSC prototype consisting of Si QD-PMMA and CdSe/CdS QD-poly(cyclohexylethylene) (PCHE) thin films is successfully fabricated with negligible agglomerate-induced scattering losses. The strong transmission tunability of a bilayer LSC, an important characteristic for agricultural applications, is also demonstrated. Analytical models for single-layer Si QD-PMMA and CdSe/CdS QD-PCHE thin film LSCs, decoupled and coupled tandem LSCs based on Si QD-PMMA and CdSe/CdS QD-PCHE thin films are also established and validated. The optimal designs of a Si QD thin-film LSC and a decoupled tandem LSC based on Si QD-PMMA and CdSe/CdS QD-PCHE thin films have been studied with the established analytical models. In addition, a neural network module in MATLAB is deployed to successfully model and predict the performance of decoupled tandem LSCs. Finally, the impact of LSC integration on greenhouses and their potential to meet the greenhouse energy demand is studied. Energy generation and transmission of LSC roofs coupled with various QDs are examined. With a 64% LSC coverage rate, CdSe/CdS, CIS/ZnS, and Si QDs can increase the entire roof energy generation by more than 30%. Compared to conventional shades, LSC roofs can transmit more red light which is beneficial for plant growth. Furthermore, detailed studies including solar radiation, greenhouse energy generation and demand, and cooling water consumption have been performed for Si QD LSC integrated greenhouses located in Arizona and Minnesota. In Arizona, Si QD LSC roofs can achieve net-zero energy (NZE) greenhouses. Significant opportunities for integrating LSCs into greenhouses to concomitantly save energy and enhance plant growth have been demonstrated.