Tuesday 4th June 2019
h. 11.30 a.m.
Seminar Room, 1st Floor, U5 building – via Roberto Cozzi 55, Milano
Lecturer: Monica Lorenzon -The Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, CA, USA; Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA
Title: Long-range FRET-mediated exciton diffusion in cesium lead halide perovskite nanocubes
Abstract. Colloidal inorganic perovskite nanocrystals (PNCs) are solution-processable functional materials whose emission can be easily tuned via both size and composition [1]. Their exciting optical properties such as the large absorption cross-section and high photoluminescence quantum yield (PLQY) make them ideal candidates for a broad range of photonics and optoelectronics applications [2]. In this work, we investigate the exceptionally efficient exciton transport enabled by Förster Resonant Energy Transfer FRET) in PNCs. With a custom-adapted microscope coupled to an optical setup, we directly measure the spatial extent of exciton hopping in a controlled two-dimensional assembly of 0D PNCs, which provides a flat energy landscape with minimal geometric disorder [3].
Steady-state and time-resolved PL microscopy, together with physical modeling of exciton transport, shows an exciton diffusion length of 200 nm, which is one order-of-magnitude longer that the values reported for chalcogen-based quantum dot solids and, importantly, matches the optical absorption depth. In addition to the exciton diffusion mapping, a significant portion of this work has been dedicated to the optimization of the substrate and the sample passivation. Specifically, we show that with a thermal-based atomic layer deposition process we are able to apply a ~3nm-thick transparent ceramic coating (aluminum oxide) which ensures optical stability over a four month period, thus overcoming the instability issue which often hinders the actual integration of perovskite materials in optoelectronics devices. Our investigation therefore provides the foundation for employing FRET-mediated exciton diffusion in nanostructured perovskites, while also demonstrating practical guidelines to use these bright emitters in optoelectronic devices beyond proof of principle.
References
[1] L. Protesescu, S. Yakunin, M. I. Bodnarchuk, F. Krieg, R. Caputo, C. H. Hendon, R. X. Yang, A. Walsh and M. V. Kovalenko, Nano Lett. 15, 6 (2015).
[2] M. V. Kovalenko, L. Protesescu and M. I. Bodnarchuk, Science, 358, 6364 (2017).
[3] G. M. Akselrod, P. B. Deotare, N. J. Thompson, J. Lee, W. A. Tisdale, M. A. Baldo, V. M. Menon and V. Bulović, Nat. Commun. 5, 3646 (2014).