Refractive indices of layers and optical simulations of Cu(In,Ga)Se2 solar cells

Romain Carron; Enrico Avancini; Thomas Feurer; Benjamin Bissig; Paolo A Losio; Renato Figi; Claudia Schreiner; Melanie Bürki; Emilie Bourgeois; Zdenek Remes; Milos Nesladek; Stephan Buecheler; Ayodhya N Tiwari

doi:10.1080/14686996.2018.1458579

Refractive indices of layers and optical simulations of Cu(In,Ga)Se₂ solar cells

Sci Technol Adv Mater. 2018 May 15;19(1):396-410. doi: 10.1080/14686996.2018.1458579. eCollection 2018.

Authors

Affiliations

¹ Laboratory for Thin films and Photovoltaics, Empa - Swiss Federal Laboratories for Materials Science and Technology, Dübendorf, Switzerland.
² Institute of Computational Physics, Zurich University of Applied Sciences (ZHAW), Winterthur, Switzerland.
³ Laboratory for Advanced Analytical Technologies, Empa - Swiss Federal Laboratories for Materials Science and Technology, Dübendorf, Switzerland.
⁴ Institute for Materials Research (IMO), Hasselt University, Diepenbeek, Belgium.
⁵ IMOMEC Division, IMEC, Diepenbeek, Belgium.
⁶ Institute of Physics, Academy of Sciences of the Czech Republic, Prague, Czech Republic.

Abstract

Cu(In,Ga)Se₂ based solar cells have reached efficiencies close to 23%. Further knowledge-driven improvements require accurate determination of the material properties. Here, we present refractive indices for all layers in Cu(In,Ga)Se₂ solar cells with high efficiency. The optical bandgap of Cu(In,Ga)Se₂ does not depend on the Cu content in the explored composition range, while the absorption coefficient value is primarily determined by the Cu content. An expression for the absorption spectrum is proposed, with Ga and Cu compositions as parameters. This set of parameters allows accurate device simulations to understand remaining absorption and carrier collection losses and develop strategies to improve performances.

Keywords: 204 Optics / Optical applications; 209 Solar cell / Photovoltaics; 306 Thin film / Coatings; 50 Energy Materials; Cu(In,Ga)Se2; absorption losses; carrier collection losses; optical losses; optical simulations; refractive index; solar cells; thin films.