Advances in Colloidal Synthesis of “Giant” Core/Thick-Shell Quantum Dots

Core/shell quantum dots (QDs) have been widely studied for their size- and composition-dependent properties and versatility for use in photonic, photovoltaic, optoelectronic, and biomedical device applications. Core/thick-shell “giant” QDs are of particular recent interest due to their advantageous optical properties such as suppression of blinking, photobleaching, and Auger recombination. Synthesizing high-quality nanostructures presents a distinct challenge for giant core/thick-shell QDs due to additional factors that complicate the nanocrystal growth mechanism. Reaction parameters must be carefully chosen to generate the structural morphology and composition for the desired core/thick-shell band structure while minimizing the formation of crystalline defects that reduce optical performance. These ideal conditions must balance competing reaction processes to grow a uniform shell while suppressing homogeneous nucleation of the large amounts of shelling material and minimizing ripening of the giant particles. This chapter presents current progress in the colloidal synthesis of “giant” core/thick-shell QDs. We first review the development of successive ionic layer adsorption and reaction (SILAR) techniques to synthesize core/thick-shell CdSe/CdS, CdSe/ZnSe, PbSe/CdSe, and PbS/CdS. The development of hot injection methods for thick-shell growth is then discussed with a particular focus on systematic studies of reaction variables for core/thick-shell CdTe/CdS. Finally, the shelling reaction mechanism is examined and we consider general experimental design criteria for the synthesis of high-quality thick-shelled QDs.