Recent Progress on Metal Chalcogenide Semiconductor Tetrapod-Shaped Colloidal Nanocrystals and their Applications in Optoelectronics

Mastery over the shape of a colloidal nanocrystal has proven to be a powerful tool to control its properties and broaden the range of applications. This is particularly relevant in the case of branched semiconductor nanocrystals, which are of special interest due to their unique optoelectronic properties. An archetypal example of a branched shape in nanocrystals is represented by particles made of a core from which four arms/pods are grown, so-called tetrapods. Many research groups have investigated these structures, driven by their potential use in optics, in which their geometry helps to efficiently capture photons from a wide range of incident angles. In addition, tetrapods have increasingly attracted much attention because of their ability to self-assemble into, for instance, percolating networks, providing an efficient way to create electronic pathways in devices that rely upon charge transport. This has stimulated in part the development of synthetic protocols to control the growth of uniform arms in particles of different sizes and, thus, to tune their functionalities, expanding the configurations that can be built via self-assembly. Recently, researchers have designed several innovative approaches for the synthesis of tetrapods, which include the combination of different material components in the same particle to achieve multiple properties. In this review, we will focus on metal chalcogenide semiconductor tetrapod-shaped nanocrystals and summarize recent progress on their synthesis methods, highlighting the various routes that aim to fabricate hybrid tetrapod nanostructures. We will examine the fundamental optoelectronic properties of tetrapod-shaped nanocrystals and provide an up-to-date overview of the strategies developed for their self-organization into different architectures. Finally, we will review their applications in photovoltaics, optoelectronics, and mechanical devices.