Synthesis of non-toxic colloidal silicon quantum dots and further optoelectronic device application

Abstract

The promising electric and optical properties lead to the wide application of zero-dimensional quantum dots (QDs) in optoelectronic devices, such as quantum dots, light-emitting diodes (QLEDs), quantum dots-based solar cells, and photodetectors. The high light absorption and tunable light emission contribute to emerging QDs to push the energy structure transform towards a more sustainable direction. Si quantum dots (Si QDs) has the advantages of low toxicity and abundant raw materials compared to the traditional toxic Cd-based QDs, which are more sustainable and attract significant interest. Substantial development for the QDs stability and structure towards the optoelectronic application has been achieved these years. This thesis developed a modified low-temperature bottom-up silicon quantum dots (Si QDs) synthesis method with precursor AEAPTMS and green reductant L-AA. High luminescence and water-stable Si QDs were obtained, which emitted bright blue-green color under a UV lamp. Purification methods, including dialysis, filtration, and centrifuge, were employed to remove the impurities and restrain the QDs aggregation. Afterward, to improve the applicability of Si QDs on photodetector devices, a solution-based ligand exchange process with 3-Mercaptopropionic acid (MPA) as the new ligand was investigated. Subsequently, the hydrocarbon chain was substituted by the shorter thiol ligand from MPA successfully. The ligand exchange Si QDs showed excellent photoluminescence emission intensity and remarkable water/ethanol stability. In addition, the lifetime of the Si-QDs increased by more than 20% and 45% compared to the non-ligand exchange ones. Besides, shorter MPA-ligand passivated Si QDs show fewer defects and better carrier transportability than the original QDs, which is more suitable for optoelectronic devices.