Rapid phosphine-free synthesis of CdSe quantum dots: Promoting the generation of Se precursors using a radical initiator

Abstract

Trace amounts of AIBN substantially accelerate the homolytic cleavage of the Se–Se bond, facilitating the phosphine-free synthesis of CdSe quantum dots. The replacement of phosphine containing compounds in the synthesis of II–VI quantum dots (QDs) via the ‘hot-injection’ method has received considerable attention in recent years, in particular toward scaling-up production. A key bottleneck in current approaches is the poor solubility of elemental Se in solvents such as 1-octadecene (1-ODE) or oleylamine requiring a heating temperature of 200 °C for several hours, or the introduction of additives such as alkylthiols or NaBH 4 , or replacement by SeO 2 . In the present work, we elucidate the fundamental steps in the dissolution of elemental Se in 1-ODE and oleylamine with the view of facilitating the large-scale synthesis of CdSe QDs. The main organoselenium species generated during the solubilisation of elemental Se in 1-ODE and oleylamine were identified by 1D and 2D NMR spectroscopy ( 1 H, 13 C and 77 Se). Experimental evidence suggests that the rate determining step is the formation of Se radicals, via homolytic cleavage of the Se–Se bond, that attack the allylic proton in 1-ODE and oleylamine. Plausible reaction pathways in both systems are proposed. Finally, we demonstrate that the radical-mediated solubilisation of Se can be significantly accelerated by the addition of azobisisobutyronitrile (AIBN), a common radical initiator used in the polymer industry. In this way, a highly concentrated Se precursor was prepared. The “hot-injection” of the Se precursor into CdO containing 1-ODE solution leads to the formation of highly luminescent CdSe QDs with a well-defined cubic structure.

Publication
Journal of Materials Chemistry A