Improving the Dispersion of Silicon/Silicon Dioxide Quantum Dots

Through the years there has been a growing need for renewable energy sources. Luminescent Solar Concentrators (LSCs) are semitransparent devices that generate renewable electricity. LSCs are composed of a transparent polymer waveguide with embedded luminescent nanocrystals. Silicon Quantum Dots (Si QDs) are semiconductor nanocrystals that broadly absorb UV light and photoluminesce near-infrared light. Si QDs are suitable for LSC applications as they are nontoxic and made from an abundant element.<br/>This work focuses on developing a method to disperse core/shell Si/SiO2 QDs in a solvent. Various aspects of the dispersion were studied by experimenting with different ligands, pH levels, and solvents. We tested two different ligands, (3-Glycidyloxypropyl) trimethoxy silane (GPTMS) and polyethylene glycol, two different pH level additives, ammonium hydroxide (NH4OH) and hydrochloric acid, and different solvents including ethanol, H2O, and toluene.<br/>The dispersions were characterized using Fourier transform infrared (FTIR), UV-Visible, and photoluminescence (PL) spectroscopies. First, the ligands GPTMS and polyethylene glycol (PEG)-silane were tested. The solution contained 100 µL of HCl, 1.5 mL of ethanol and 0.3 mL of H2O. The dispersion of the Si/SiO2 with GPTMS and HCl settled faster than the Si/SiO2 with PEG-silane and HCl dispersion. Using UV-Vis, the Si/SiO2 with GPTMS absorbance is higher than the absorbance of the Si/SiO2 with PEG-silane due to scattering from the larger agglomerates that settled. The samples in HCl were more stable than ones using ammonium hydroxide. FTIR measurements confirmed that the Si/SiO2 QDs were coated with PEG-Silane.<br/>Lastly the dispersions were characterized using photoluminescence spectroscopy. The Si/SiO2 QDs in toluene and Si/SiO2 QDs in PEG-silane show that the solutions can have similar photoluminescence intensities even though the toluene dispersion sample agglomerates. Si/SiO2 QDs in H2O agglomerate faster relative to the QDs in ethanol. In conclusion, using PEG-silane as a ligand in an acidic environment with a polar solvent led to a stable, homogeneous mixture with a high photoluminescence intensity.