Optoelectronic applications of gemini surfactants: Quantum dots stabilization

Quantum dots (QDs) are nanostructured semiconductor materials whose optical and electrical characteristics can be modified through manipulation of the dimensions of the quantum dot. These materials can be utilized for numerous application areas including light-emitting diodes, solar cells, sensors, and flexible electronics; however, due to their large surface area relative to volume, they are highly susceptible to reactions with their surroundings (causing aggregation) as well as defects on their surfaces. As a result, it is necessary to employ innovative stabilization methods to ensure QDs maintain their luminescence efficiency when subjected to the elements. The focus of this review is to provide an overview of recent research using gemini surfactants to stabilize quantum dots and combine their unique optical and electrical properties into optoelectronic devices. Each section of the review provides insights into the molecular structure of gemini surfactants, how they behave during micelle formation, how they stabilize QDs during their fabrication, and how these surfactants influence both the arrangement of QD particles within the device, as well as their assembly into a completed product. The key factors identified in this body of work include the length of the spacer connecting the head groups to the tails, the chemical composition of the head groups, and the critical micelle concentrations at which these surfactants are most effective at stabilizing QDs against degradation from the elements. The article reviewed indicates that research into the effect of these new types of surfactant (gemini surfactants) on the properties of solvent-solute interactions shows that they have a significantly lower CMC than single-chain surfactants, have a much more compact and well-organized interfacial layer due to their larger molecular weight, have greater electrostatic and steric stabilizing properties than single-chain surfactants, and therefore offer improved colloidal stability (smaller base size), retention of photoluminescence at an increased level compared to single-chain surfactants, and, consequently, improved device performance when using QD optoelectronic devices. Though challenges remain regarding scalability, toxicity, and regulatory constraints, the unique structure of gemini surfactants, combined with green synthesis strategies, will allow for continued advancement of this unique class of surfactants and their application in the production of QD technology for use in commercial applications.