Morphology and Band Structure of Orthorhombic PbS Nanoplatelets: An Indirect Band Gap Material
David Macias a b, Carlos Echeverría a, Iván Mora a, Juan Ignacio Climente b
a Institute of Advanced Materials (INAM), Universitat Jaume I, 12071 Castelló de la Plana, Spain
b Departament de Química Física i Analítica, Universitat Jaume I, Av. Vicent Sos Baynat, s/n, Castellón de la Plana, Spain
Online School
Proceedings of Online school on Fundamentals of Semiconductive Quantum Dots (QDsSCHOOL)
Online, Spain, 2021 May 11th - 13th
Organizers: Quinten Akkerman, Sergio Brovelli and Liberato Manna
Poster, David Macias, 017
DOI: https://doi.org/10.29363/nanoge.qdsschool.2021.017
Publication date: 30th April 2021
ePoster: 

PbS quantum dots and nanoplatelets (NPLs) are of enormous interest in the development of optoelectronic devices. However, some important aspects of their nature remain unclear. Recent studies have revealed that colloidal PbS NPLs may depart from the rock-salt crystal structure of bulk and form an orthorhombic (Pnma) modification instead[1,2]. To gain insight into the implications of such a change over the optoelectronic properties, we have synthesized orthorhombic PbS NPLs and determined the lattice parameters by means of selected area electron diffraction measurements. We have then calculated the associated band structure using density functional theory with  Perdew−Burke−Ernzerhof functional for solids and with the GW approximation, including spin−orbit interactions. An indirect band gap is found, which may explain the weak luminescence reported in experiments. We derive effective masses for conduction and valence bands and deduce that quantum confinement along the a crystallographic axis (short axis of the NPL) reinforces the indirect band gap but that along b and c axes favors a direct gap instead[3] .
Calculations for colloidal nanoplatelets of 1.8 nm thickness, carried out with k·p theory [4], show that excitonic effects are strong, with binding energies of about 150 meV.

 

[1] A. H. Khan, et al. Chemistry of Materials 29, 2883 (2017).

[2] Q. A. Akkerman, et al. Chemistry of Materials 31, 8145 (2019).

[3] D. F. Macias, et al. Chemistry of Materials 33, 420 (2021).

[4] F. Rajadell, et al. Physical Review B 96, 035307 (2017)

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