Eur. Phys. J. B (2018) 91: 215
https://doi.org/10.1140/epjb/e2018-90206-6

Regular Article

Size-dependent optical absorption of Cu₂ZnSn(Se,S)₄ quantum dot sensitizers from ab initio many-body methods^★,★★

¹ Institut Lumière Matière, UMR5306 Univerité Lyon 1–CNRS, 69622 Villeurbanne Cedex, France
² Institut für Festkörpertheorie und -optik, Friedrich-Schiller-Universität Jena, Max-Wien-Platz 1, 07743 Jena, Germany
³ Institut Néel, Université Grenoble Alpes and CNRS, 38042 Grenoble Cedex 9, France
⁴ European Theoretical Spectroscopy Facility and Institut für Physik, Martin-Luther-Universität Halle-Wittenberg, 06099 Halle, Germany
⁵ European Theoretical Spectroscopy Facility and Institut für Festkörpertheorie und -optik, Friedrich-Schiller-Universität Jena, Max-Wien-Platz 1, 07743 Jena, Germany

^a e-mail: skoerbel@uni-muenster.de
^b e-mail: silvana.botti@uni-jena.de

Received: 26 March 2018
Received in final form: 15 June 2018
Published online: 1 October 2018

Abstract

Quantum-dot sensitized solar cells are an exciting technology because they allow to overcome the efficiency limit of single-junction solar cells. The tunability of their band gap with quantum-dot size allows to make multi-junction solar cells with optimized band gaps, moreover using simple production techniques. Here, we study quantum-dot sensitizers made of the earth-abundant photovoltaic absorbers Cu₂ZnSnS₄ and Cu₂ZnSnSe₄ (CZTS). Using many-body perturbation theory (GW and the Bethe–Salpeter equation) and time-dependent density-functional theory, we calculate the dependence of the photoemission and optical band gap on the quantum-dot size, accounting for excitonic effects. Our study completes the existing knowledge about quantum confinement in CZTS nanocrystals, for which experimental data are sparse and provide the power law that describes the dependence of the optical gap on the quantum-dot size.