Exciton diffusion in two-dimensional metal-halide perovskites
Michael Seitz a b, Alvaro Magdaleno a b, Nerea Alcázar-Cano a c, Marc Meléndez a c, Tim Lubbers a b, Sanne Walraven a b, Sahar Pakdel d, Elsa Prada a b, Rafael Delgado-Buscalioni a c, Ferry Prins a b
a Condensed Matter Physics Center (IFIMAC), Autonomous University of Madrid, Madrid, Spain
b Condensed Matter Physics Center (IFIMAC), Autonomous University of Madrid, Madrid, Spain
c Department of Theoretical Condensed Matter Physics, Autonomous University of Madrid, Madrid, Spain
d Department of Physics and Astronomy, Aarhus University, Denmark, Denmark
Poster, Michael Seitz, 041
Publication date: 23rd April 2020

There is an increasing interest in two-dimensional (2D) Ruddlesden-Popper perovskites for solar harvesting and light emitting applications due to their superior chemical stability as compared to bulk perovskites.[1,2] Both, purely 2D and blends of 2D/3D phases have been successfully employed in solar cells with an efficiencies of >18% and >21%, respectively.[3,4] As with earlier advances in the field of perovskites, these technological improvements are advancing at a pace that far exceeds our understanding of the physical mechanisms underlying their performance. Particularly, the reduced dimensionality in 2D perovskites results in excitonic excited states which dramatically modify the dynamics of charge collection. While the carrier dynamics in bulk systems is increasingly well understood, a detailed understanding about the spatial dynamics of the excitons in 2D perovskites is lacking.[5]


Here, we present the direct measurement of the intrinsic diffusivities and diffusion lengths of excitons in single crystalline 2D perovskites using time-resolved microscopy. Our technique allows us to follow the temporal evolution of a diffraction limited exciton population with sub-nanosecond resolution revealing the spatial and temporal exciton dynamics. We reveal two distinct temporal regimes: For early times excitons undergo unobstructed normal diffusion, while at later times exciton transport becomes subdiffusive as excitons get trapped. Using the versatility of perovskite materials, we study the influence of the organic spacer, cation and dimensionality (n = 1 and 2) on the diffusion dynamics of excitons in 2D perovskites. We find that changes in these parameters can yield diffusivities which differ in up to one order of magnitude. We show that these changes arise due to strong exciton-phonon interactions and potentially with the formation of large exciton-polarons. Our results provide insight into how excitons diffuse through 2D perovskites and yield clear design parameters for more efficient 2D perovskite solar cells and light emitting devices.[6]


[6] Seitz, M. et al. ArXiv (2020). doi: http://arxiv.org/abs/2001.05704

This work has been supported by the Spanish Ministry of Economy and Competitiveness through The “María de Maeztu” Program for Units of Excellence in R&D (MDM-2014-0377). M.S. acknowledges the financial support of a fellowship from ”la Caixa” Foundation (ID 100010434). The fellowship code is LCF/BQ/IN17/11620040. M.S. has received funding from the European Union’s Horizon 2020 research and innovation program under the Marie Skłodowska-Curie grant agreement No. 713673. F.P. acknowledges support from the Spanish Ministry for Science, Innovation, and Universities through the state program (PGC2018-097236-A-I00) and through the Ramón y Cajal program (RYC-2017-23253), as well as the Comunidad de Madrid Talent Program for Experienced Researchers (2016-T1/IND-1209). N.A., M.M. and R.D.B. acknowledges support from the Spanish Ministry of Economy, Industry and Competitiveness through Grant FIS2017-86007-C3-1-P (AEI/FEDER, EU). E.P. acknowledges support from the Spanish Ministry of Economy, Industry and Competitiveness through Grant FIS2016-80434-P (AEI/FEDER, EU), the Ramón y Cajal program (RYC-2011- 09345) and the Comunidad de Madrid through Grant S2018/NMT-4511 (NMAT2D-CM). S.P. acknowledges financial support by the VILLUM FONDEN via the Centre of Excellence for Dirac Materials (Grant No. 11744).

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