Dark and Bright Excitons in Halide Perovskite Nanoplatelets

Advanced Science

Alexander L. Efros¹  Michael W. Swift¹  John L. Lyons¹  Peter C. Sercel²  Markus Döblinger³  Carola Lampe⁴  Alexander S. Urban⁴  Moritz Gramlich⁴ 

[1] Center for Computational Materials Science U.S. Naval Research Laboratory Washington D.C. 20375 USA;Center for Hybrid Organic Inorganic Semiconductors for Energy Golden CO 80401 USA;Department of Chemistry Ludwig‐Maximilians‐Universität München (LMU) & Center for NanoScience (CeNS) Munich 81377 Germany;Nanospectroscopy Group Nano‐Institute Munich Department of Physics Ludwig‐Maximilians‐Universität München (LMU) Munich 80539 Germany;

关键词: effective mass model;    exciton fine structure;    halide perovskites;    nanoplatelets;    optoelectronics;    photoluminescence spectroscopy;   

DOI  :  10.1002/advs.202103013

来源: DOAJ

【 摘 要 】

Abstract Semiconductor nanoplatelets (NPLs), with their large exciton binding energy, narrow photoluminescence (PL), and absence of dielectric screening for photons emitted normal to the NPL surface, could be expected to become the fastest luminophores amongst all colloidal nanostructures. However, super‐fast emission is suppressed by a dark (optically passive) exciton ground state, substantially split from a higher‐lying bright (optically active) state. Here, the exciton fine structure in 2–8 monolayer (ML) thick Csn − 1PbnBr3n + 1 NPLs is revealed by merging temperature‐resolved PL spectra and time‐resolved PL decay with an effective mass model taking quantum confinement and dielectric confinement anisotropy into account. This approach exposes a thickness‐dependent bright–dark exciton splitting reaching 32.3 meV for the 2 ML NPLs. The model also reveals a 5–16 meV splitting of the bright exciton states with transition dipoles polarized parallel and perpendicular to the NPL surfaces, the order of which is reversed for the thinnest NPLs, as confirmed by TR‐PL measurements. Accordingly, the individual bright states must be taken into account, while the dark exciton state strongly affects the optical properties of the thinnest NPLs even at room temperature. Significantly, the derived model can be generalized for any isotropically or anisotropically confined nanostructure.

【 授权许可】

Unknown