Synthesis of Colloidal Quantum Dot Nanostructures for Photon Upconversion

Colloidal quantum dots (QDs) are promising materials for photon upconversion, the process by which multiple low-energy photons are absorbed and one higher-energy photon is emitted. Recent efforts have focused on developing complex multi-shell and nanorod-based heterostructures as efficient photon upconverters for solar energy harvesting applications. Here we present a CdTe/CdS/CdSe core/shell/shell QD platform for photon upconversion with several advantages over an analogous rod-based platform. This tunable platform featuring a thick CdS layer can realize a significant shift toward the optimal wavelengths for solar energy harvesting. As a first step toward realizing upconversion in this platform, we modify established colloidal synthesis procedures to enable a high degree of control over particle morphology and size. Through transmission electron microscopy (TEM) and photoluminescence (PL) characterization, we confirm successful product formation with a high degree of control over the shell thicknesses and resulting PL emission wavelengths. We also synthesize CdTe/CdS intermediates with CdS layers of various increasing thicknesses, an important tool to facilitate the charge carrier separation necessary for efficient photon upconversion.