EventMaksym Kovalenko

Highly Luminescent Nanocrystals of Cesium and Formamidinium Lead Halide Perovskites: From Discovery to Applications

We discuss the discovery and recent developments of colloidal lead halide perovskite nanocrystals (LHP NCs, NCs, A=Cs+, FA+, FA=formamidinium; X=Cl, Br, I) [1,2,3] and some lead-free analogues. We survey the synthesis methods, optical properties and prospects of these NCs for optoelectronic applications, foremost as classical and quantum light sources [4,5].

LHP NCs exhibit spectrally narrow (<100 meV, 12-45 nm from blue-to-near-infrared) sponaneous and stimulated emission, originating form bright triplet excitons [6], and tunable over the entire visible spectral region of 400-800 nm [1-4]. Post-synthestic chemical transformations of colloidal NCs, such as ion-exchange reactions, provide an avenue to compositional fine-tuning or to otherwise inaccessible materials and morphologies [7]. Cs- and FA-based perovskite NCs are highly promising for backlighting of LCD displays, for light-emitting diodes and as precursors/inks for perovskite solar cells. Towards these applications, a unique feature is that perovskite NCs appear to be trap-free without any electronic surface passivaiton [8], in spite of having structural defects.

The processing and optoelectronic applications of perovskite NCs are, however, hampered by the loss of colloidal stability and structural integrity due to the facile desorption of surface capping molecules during isolation and purification. To address this issue, we have develop new ligand capping strategy utilizing common and inexpensive long-chain zwitterionic molecules, resulting in much improved chemical durability [9].

Perovskite NCs also readily form long-range ordered asssemblies known as superlattices. These assemblies exhibit accelerated coherent emission (superfluorescence) [10], not observed before in semiconductor nanocrystal superlattices.

Maksym Kovalenko abs

About The Speaker

Maksym Kovalenko

Maksym Kovalenko has been an associate professor (with tenure) of Functional Inorganic Materials since January 2017 and a Head of the Institute of Inorganic Chemistry at ETH Zurich since January 2018. He jointed ETH Zurich in summer 2011 as a tenure-track assistant professor. Previously, he had completed doctoral studies at the University of Linz, (Austria, 2004-2007) and postdoctoral training at the University of Chicago (USA, 2008-2011). The research activities of M. Kovalenko and his group focus on chemistry, physics and applications of inorganic solid-state materials and nanostructures. In particular, present research efforts concern: (i) the precision synthesis of highly luminescent semiconductor nanocrystals; (ii) nanocrystal surface chemistry; (iii) exploration of novel semiconductor materials by solution- and solid-state synthesis; (iv) novel semiconductors for hard radiation detection; (iv) novel materials and concepts for Li-ion and post-Li-ion rechargeable batteries. Many of these activities are strongly linked to industrial partners. Academic collaborations involve various groups ranging from first-principles theory of materials to applications in photovoltaics and thermoelectrics. He is also affiliated with Empa (Swiss Federal Laboratories for Materials Science and Technology). To date, Maksym Kovalenko has published ca. 230 scientific publications in international leading journals, co-authored 3 book chapters, and is listed as an inventor on 11 patents. He has been the recipient of highly prestigious awards including  Rössler Prize (2019), ERC Consolidator Grant (2018), ERC Starting Grant (2012), Ruzicka Preis (2013), and Werner Prize (2016). He also serves as an associate editor of the Chemistry of Materials.