Beyond Ideal: Defects and Disorder in Semiconductor Nanocrystals

Rémi Beaulac, Deparment of Chemistry, Michigan State University, 220 Trowbridge Rd, East Lansing, MI 48824, USA

Colloidal semiconductor nanocrystals (NCs) share the fascinating electronic, optical, and chemical properties that characterize all semiconductor materials. Like their bulk counterparts, the electronic structure of NCs is highly delocalized in space, but without the translational periodicity associated with (pseudo)-infinite lattices, leading to electronic excitations that are highly sensitive on the overall size and shape of the semiconductor nanocrystals, an effect designated under the term “quantum confinement”. As a consequence, NCs are particularly well-suited for a host of applications – optical sensing and imaging, light-emission, photovoltaics, or photo-redox transformations – that rely on the extraction of work, of one form or another, from electronically-excited NCs. Such energy-conversion schemes necessarily require control over the energetic configuration of NC electronic structure as well as the ability to limit undesired excited-state relaxation pathways that lead to direct energetic losses by rapid excitonic recombination. Unfortunately, the photophysical behavior of NCs is often complex, associated with multi-exponential excited-state dynamics, optically-dark trap states, and luminescence intermittency, to name but a few of the phenomena that impede the development of NC-based applications. This presentation will highlight recent efforts by our group to characterize and manipulate the microscopic nature of specific defects that directly govern optical properties such as plasmonic resonances and non-radiative recombination, demonstrating that not all defects are created equal, and that defective NCs can often be associated with desirable characteristics that cannot be obtained from perfect nanostructures.

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Cette conférence est présentée par le RQMP Versant Nord du Département de physique de l'Université de Montréal et le Département de génie physique de Polytechnique Montréal.