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Jean-Christophe Blancon1 Wanyi Nie1 Hsinhan Tsai2 Constantinos Stoumpos3 Mikael Kepenekian4 Sergei Tretiak1 Pulickel Ajayan2 Mercouri Kanatzidis3 Jacky Even5 Claudine Katan4 Jared Crochet1 Aditya Mohite1

1, Los Alamos National Laboratory, Los Alamos, New Mexico, United States
2, Rice University, Houston, Texas, United States
3, Northwestern University, Evanston, Illinois, United States
4, Université de Rennes 1, Rennes, , France
5, INSA de Rennes, Rennes, , France

Understanding and controlling charge and energy flow in state-of-the-art semiconductor quantum-wells has enabled high-efficiency optoelectronic devices. Two-dimensional Ruddlesden-Popper layered perovskites (RPPs) have recently emerged as an alternative to the classic bulk organic-inorganic hybrid perovskites, mainly due to significantly improved photo- and chemical-stability in optoelectronic devices [1]. Few recent encouraging developments in optoelectronic applications, notably in energy harvesting and light emitting [1-3], have already been demonstrated in these two-dimensional layered perovskites. RPPs are solution-processed quantum-wells wherein the band gap can be tuned by varying the perovskite layer thickness, which modulates the effective electron-hole confinement. We report that, counterintuitive to classical quantum-confined systems where photo-generated electrons and holes are strongly bound by Coulomb interactions or excitons, the photo-physics of thin films made of Ruddlesden-Popper perovskites with a thickness exceeding two perovskite crystal-units (>1.3 nanometers) is dominated by lower energy states associated with the local intrinsic electronic structure of the edges of the perovskite layers [3]. These states provide a direct pathway for dissociating excitons into longer-lived free-carriers that significantly improve the performance of solar cell devices.

References
[1] Tsai et al., Nature (2016), 536, 312-316.
[2] M. Yuan et al., Nat. Nanotechnol. (2016), 11, 872-877.
[3] Blancon et al., Science (2017), 355, 1288-1292.

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