Semiconductor Nanocrystals: Unveiling the Chemistry behind Different Facets

Conspectus Developing next-generation colloidalsemiconductornanocrystals with high-quality optoelectronic properties and preciseprocessability relies on achieving complete mastery over the surfacecharacteristics of nanocrystals (NCs). This requires precise engineeringof the ligand-NC surface interactions, which poses a challengedue to the complex reactivity of the multiple binding sites acrossthe entire surface. Accordingly, recent progress has been made bystrategically combining well-defined surface models with quantitativesurface reactions to advance our understanding and manipulation ofNC surface chemistry. Our lab has contributed to this progress bydeveloping a size-dependent shape model of IV-VI NCs, gaininginsights into their unique facet-specific chemistry, and developinga systematic ligand modification strategy for target applications.Furthermore, we have created well-defined facets in III-V NCsvia a co-passivation strategy, addressing the previously lacking specificshapes. This Account is divided into three parts. First, wediscuss thecomplexities involved in comprehensively understanding the nanocrystalsurface structure at the atomistic level. We explain why we focusedon well-defined NCs with a large exciton Bohr radius to explore facets,an essential aspect of surface heterogeneity across the entire NC.Second, we present our work on one of the most studied nanocrystals,IV-VI materials, and how facet-specific surface chemistry hasled to a meaningful understanding and control of the NC's surface.We discovered a size-dependent facet distribution in IV-VINCs and suggested facet-specific surface chemistry to improve thephotophysical properties of NCs. We further modulate the electronicproperties of NC assemblies for efficient optoelectronic applications.Third, we describe our recent success in achieving well-defined facetsand their facet-specific chemistry in III-V NCs, which haveyet to be explored as much as classical II-VI or IV-VImaterials. We explain how controlling the surfaces in III-VNCs has been challenging. We present a precise growth platform forthe geometric modulation of NCs, which can be further explored forshape-dependent exciton behavior and surface reactivities. Takentogether, we present a compelling case for utilizing facet-specificchemistry as a platform for mechanistic investigation and morphologyexploration, which can pave the way for developing high-quality andprecisely designed NCs for optoelectronic technologies, unlockingnew multidisciplinary applications.