Low Dimensional Colloidal Nano-Perovskites Not Your Usual Quantum Dots

seminars
16.11.2017
14:30
David Wang Auditorium, 3rd floor Dalia Maydan Bldg.
Dr. Yehonadav Bekenstein

Dr. Yehonadav Bekenstein 1,2,3

1Department of Chemistry, University of California, Berkeley, California 94720, USA.

2Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.

3Kavli Energy NanoScience Institute, University of California, Berkeley, California 94720, USA.

Thermodynamic considerations suggest correlation between efficient photo conversion and bright luminescence, in practice we do not usually see that. However, lead-halide perovskites do show excellent efficiencies in both photovoltaic and light-emitting applications. We study perovskite nanocrystals as a model system to further understand the origin of their enigmatic properties.

Low-dimensional colloidal nano-crystals of cesium lead halide demonstrate exceptionally bright emission without shelling and unusual room temperature transformation not common to other semiconductors nanocrystals. These properties suggest a near equilibrium nanocrystal system. In a series of studies we follow the formation and transformations of these nanocrystals. We can now grow quantum confined cesium lead halide nanocrystals with cube, plate and wire shapes and with atomic precision. We demonstrate how quantum confinement and dimensionality dictate the exciton behavior and photophysical properties of these crystals. In the case of two dimensional nanoplates we observe strong quantum confinement of the excitons.(1) In the case of nanowires we show that broken symmetry manifests in significant polarized emission. These nanowires can be further utilized through 3D printing and alignment process to fabricate highly polarized functional metamaterials. In addition to the synthetic shape control, further control of the optical properties is achieved by changing the anion composition. The “softness” of the perovskite crystal allows post synthetic room temperature transformations that tune the material band-gap values throughout the visible spectrum.(2-3) The resulting high quantum yield, combined with the synthetic versatility and facile transformations, position colloidal perovskites as a unique model system for the study of charge dynamics and thermodynamic transformations at the nanoscale, contributing to the understanding of next generation materials for energy. Future developments in perovskites, leading to more stable and lead free materials will also be discussed.

(1) Bekenstein, Y.; Koscher, B. A.; Eaton, S. W.; Yang, P.; Alivisatos, A. P. J. Am. Chem. Soc. 2015, 137 (51), 16008.

(2) Zhang, D.; Yang, Y.; Bekenstein, Y.; Yu, Y.; Gibson, N. A.; Wong, A. B.; Eaton, S. W.; Kornienko, N.; Kong, Q.; Lai, M.; Alivisatos, A. P.; Leone, S. R.; Yang, P. J. Am. Chem. Soc. 2016, 138 (23), 7236.

(3) Liu, Z.; Bekenstein, Y.; Ye, X.; Nguyen, S. C.; Swabeck, J.; Zhang, D.; Lee, S.-T.; Yang, P.; Ma, W.; Alivisatos, A. P. J. Am. Chem. Soc. 2017, 139 (15), 5309.