Colloidal semiconductor nanocrystals (NCs) possess a variety of fascinating electronic, optical, and chemical properties that make them 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 non-radiative recombination. Unfortunately, the photophysical behavior of NCs is often complex and 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 and which point to the role that surface states play in modulating the “core” electronic properties of the nanocrystals. Indeed, surfaces can significantly impact the desirable electronic properties associated with the nanocrystal core atoms, most notoriously by providing low-lying electronic states that lead to efficient non-radiative excitonic recombination pathways. This presentation will highlight recent efforts by our group [1, 2] to characterize and manipulate the microscopic nature of specific surface defects that directly or indirectly govern phenomena such as non-radiative recombination and donor-acceptor transfer processes, demonstrating that not all defects are created equal, and emphasizing the need to develop approaches that explicitly take into consideration the distributed nature of surface defects in order to extract meaningful information out of the complex dynamics of semiconductor nanostructures.

Unravelling the complex excited-state dynamics of semiconductor nanocrystals

2019 Spring National Meeting

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