The facile synthesis and excellent optoelectronic properties of all-inorganic perovskite quantum dots has attracted considerable attention among academic researchers; however, accessing the highest quality materials is crucial to fundamentally understanding the performance limits of that material. While the facile low temperature synthesis of these materials affords easy access to the material, it also opens the door for a number of very real problems, most notably the presence of defects. While it is generally accepted that the perovskites have a somewhat unusual defect tolerance, they are not defect impervious, particularly when considering surface states. We investigated the role that shallow surface states play in the optical properties of CsPbBr3 nanocrystals, resulting in sub-unity quantum yields and multi-exponential excited state lifetimes. While a material that performs with up to 90% quantum yield following the synthesis is encouraging, it begs the question: what prevents that value from being truly unity? Through a series of salt-based surface treatments, we demonstrate most notably a thiocyanate-based treatment that is capable of boosting the photoluminescence quantum yield to within measurement error of unity while transforming the excited state lifetime to something described by single exponential kinetics, an unusual property that is not seen in many other near-unity quantum yield materials. In our work, we demonstrate that postsynthetic salt treatments are able to very effectively alter the lead-rich surface typical in CsPbBr3 perovskite quantum dots, affording access to the highest performing materials. Being able to access the highest quality materials removes some of the uncertainty that arises from non-ideal materials. This access will be crucial to determining and understanding the truly unique aspects of perovskite quantum dots, and how to best utilize them moving forward.

Postsynthetic surface treatments for essentially trap-free CsPbBr3 colloidal nanocrystals

255th National Meeting (2018)

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