Binary Thiourea Precursors Enable Continuous Size Control of PbS Quantum Dots

Lead sulfide (PbS) colloidal quantum dots (QDs) are promising materials for next-generation optoelectronic devices, such as light-emitting diodes and photodetectors. However, conventional synthetic methods for PbS QDs rely on the use of a wide range of thiourea-based precursors with varying reactivities to achieve size control. To simplify the size control process, we have developed a binary thiourea precursor strategy for controlling the size of PbS QDs, where control relies exclusively on the ratio of two precursors. By adjustment of the ratio of the high- and low-reactivity thiourea precursors, this strategy precisely controls the overall reaction kinetics, allowing for a regulated nucleation process and resulting in PbS QDs with tunable sizes from 2.9 to 6.1 nm and a first excitonic absorption peak spanning 920 to 1590 nm. The kinetics of the binary thiourea-controlled nucleation process were examined by ultraviolet–visible spectroscopy, whereas the high monodispersity of the synthesized QDs was confirmed by transmission electron microscope analysis. This work presents a simplified, cost-effective strategy for the precise size control of high-quality PbS QDs.