Colloidal Synthesis Methods of Atomically Flat Complex Nanocrystal Heterostructures
Colloidal quantum wells (CQWs), also known as nanoplatelets (NPLs), are a highly favorable family of semiconductor nanocrystals owing to their attractive optical characteristics. Because of their quasi-two-dimensional and atomically flat structure, they exhibit one-dimensional quantum mechanical confinement in the vertical direction. Thanks to this strong quantum confinement, they have shown to be very promising for a vast range of optoelectronic applications including light-harvesting (e.g., luminescent solar concentrators and energy transfer systems) and light-generation (e.g., lasers and LEDs). In addition, their properties can be tuned and enhanced by using various heterostructures of the NPLs, including core/crown and core/shell architectures in which extensions of other semiconductors or their alloys can be selectively grown in the lateral and/or vertical directions, making heterostructures of these NPLs. Among such heterostructure growth techniques, colloidal-atomic layer deposition (c-ALD) and hot injection (HI) of shell coating have gained attention owing to their atomically precise coating and high throughput. In particular, HI enables coating of a large number of monolayers on top of the core NPL seeds, achieving high photoluminescence quantum yields (PL-QYs), which can reach near unity, while c-ALD benefits from layer-by-layer controlled deposition, preferable for the precise implementation of complex heterostructure designs. Alongside with the shell coating, growing crown in the lateral direction can effectively passivate the peripheral side of NPLs and enhance their PL-QYs. In our research work, we develop these colloidal synthesis methods and synthesize engineered NPLs with desired optical, electrical and chemical properties. Developing such complex quasi-2D NPL heterostructures with engineered electronic band structure is intended to lead to highly efficient nano-emitters for next-generation colloidal lasing applications.