(143e) Engineered Quantum Dots for Light Selective Polymer Films with High Photoluminescence and Photostability

This work focused on optimizing the optical properties of polymer films using quantum dot (QD) nanoparticles to manipulate and control light transmission for applications in light selective nanofilms. A new approach was undertaken to synthesize Quantum Dots (QDs) with highly luminescent properties and photostability for solar energy applications.  Highly luminescent Cd- based and non Cd-based QDs: CdS, ZnS, ZnSeS, and CdS/ZnS core/shell QDs with 5 nm size were synthesized using a facile approach based on pyrolysis of the single molecule precursors. After capping the CdS QDs with a thin layer of ZnS to reduce toxicity, the photoluminescence and photostability of the core-shell QDs was significantly enhanced. The ZnS shell was found to passivate the surface defects of the CdS dots while confining the electron-hole pair to the CdS core region.

To make both the bare and core/shell structure QDs more resistant against photochemical reactions, a mesoporous silica layer was grown on the QDs through a reverse microemulsion technique based on hydrophobic interaction and surface silanization using 3-mercaptopropyl trimethoxysilane as the coupling agent. The average size of the mesoporous silica nanoparticles (MSNs) was 60 nm with tuneable QDs core from 10-35nm depending on the concentration of QDs loaded. This encapsulation improved the quantum yield 40% and photostability 30% compared to the bare QDs by providing much stronger resistance to oxidation and Oswald ripening of QDs. Various silane coupling agents are being examined to  chemically attach these silica covered QDs to poly(ethylene vinyl acetate) polymer that provides simultaneous UV protection, infrared retention, and light selectivity for controlling plant growth, ultimately working to improve biomass production and reduce energy consumption in commercial greenhouses. A new type of environmental friendly quantum dot-sensitized photovoltaic device was also developed by decorating QDs using supercritical carbon dioxide (scCO₂). With a liquid electrolyte as the hole transport medium, quantum-dot-sensitized nanowire photovoltaic cells exhibited short-circuit currents ranging from 1 to 2 mA/cm² and open-circuit voltages of 0.5−0.6 V, when illuminated with 100 mW/cm² simulated AM1.5 spectrum. Internal quantum efficiencies as high as 30−50% were also obtained.