Thermodynamic stability, phase separation and Ag grading in (Ag,Cu)(In,Ga)Se2 solar absorbers

Kostiantyn V. Sopiha; Jes K. Larsen; Olivier Donzel-Gargand; Faraz Khavari; Jan Keller; Marika Edoff; Charlotte Platzer-Björkman; Clas Persson; Jonathan J. S. Scragg

doi:10.1039/D0TA00363H

Thermodynamic stability, phase separation and Ag grading in (Ag,Cu)(In,Ga)Se₂ solar absorbers†

Kostiantyn V. Sopiha,

*^a Jes K. Larsen,

^a Olivier Donzel-Gargand,

^a Faraz Khavari,

^a Jan Keller,

^a Marika Edoff,

^a Charlotte Platzer-Björkman,

^a Clas Persson

^bc and Jonathan J. S. Scragg

Author affiliations

* Corresponding authors

^a Solar Cell Technology, Department of Materials Science and Engineering, Uppsala University, Box 534, SE-75121 Uppsala, Sweden
E-mail: kostiantyn.sopiha@gmail.com

^b Department of Materials Science and Engineering, KTH Royal Institute of Technology, SE-100 44 Stockholm, Sweden

^c Center for Materials Science and Nanotechnology, Department of Physics, University of Oslo, P.O. Box 1048 Blindern, NO-0316 Oslo, Norway

Abstract

Gallium alloying and grading in Cu(In,Ga)Se₂ (CIGS) are well-established strategies for improving performance of thin-film solar cells by tailoring band profiles within the absorber. Similarly, Ag incorporation is considered to be an effective complementary route towards further advancement of the field. Herein, we explore thermodynamics of the formation of (Ag,Cu)(In,Ga)Se₂ (ACIGS) alloy. Using first-principles methods, we reveal the existence of a miscibility gap in the Ga-rich alloys at temperatures close to those employed for the co-evaporation growth. We demonstrate that this property can result in phase separation and the formation of Ag gradients throughout the film thickness. We prove experimentally that the phase separation can indeed occur during low-temperature growth and/or post-deposition treatments. Furthermore, we uncover the anticorrelation between Ag and Ga contents, and demonstrate thermodynamically-driven formation of [Ag]/([Ag] + [Cu]) gradients in films with a steep [Ga]/([Ga] + [In]) profile. Finally, we discuss how these phenomena can influence solar cell devices. The presented results are expected to provide fundamental insight into the physics of growth and processing of ACIGS absorbers, which could be utilized to further boost the efficiency of thin-film solar cells.

Supplementary files

Article information

DOI: https://doi.org/10.1039/D0TA00363H
Article type: Paper
Submitted: 09 Jan 2020
Accepted: 12 Apr 2020
First published: 13 Apr 2020
This article is Open Access

Download Citation

J. Mater. Chem. A, 2020,8, 8740-8751

Permissions

Request permissions

Thermodynamic stability, phase separation and Ag grading in (Ag,Cu)(In,Ga)Se₂ solar absorbers

K. V. Sopiha, J. K. Larsen, O. Donzel-Gargand, F. Khavari, J. Keller, M. Edoff, C. Platzer-Björkman, C. Persson and J. J. S. Scragg, J. Mater. Chem. A, 2020, 8, 8740 DOI: 10.1039/D0TA00363H

This article is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported Licence. You can use material from this article in other publications, without requesting further permission from the RSC, provided that the correct acknowledgement is given and it is not used for commercial purposes.

To request permission to reproduce material from this article in a commercial publication, please go to the Copyright Clearance Center request page.

If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given.

If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party commercial publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page.

Journal of Materials Chemistry A