A direct measure of positive feedback loop-gain due to reverse bias damage in thin-film solar cells using lock-in thermography
IEK5-Photovoltaik, Forschungszentrum Jülich GmbH, 52425 Jülich, Germany
2 Faculty of Electrical Engineering and Information Technology, RWTH Aachen University, Mies-van-der-Rohe-Strasse 15, 52074 Aachen, Germany
* e-mail: email@example.com
Received in final form: 22 September 2022
Accepted: 25 November 2022
Published online: 9 January 2023
In this work, we present a method to study thermal runaway effects in thin-film solar cells. Partial shading of solar cells often leads to permanent damage to shaded cells and degrades the performance of solar modules over time. Under partial shading, the shaded cells may experience a reverse bias junction breakdown. In large-area devices such as solar cells, this junction breakdown tends to take place very locally, thus leading to very local heating and so-called “hot-spots”. Previously, it was shown that a positive feedback effect exists in Cu(In,Ga)Se2 (CIGS) thin-film solar cells, where a highly localized power dissipation is amplified, which may lead to an unstable thermal runaway process. Furthermore, we introduced a novel characterization technique, laser induced Hot-Spot Lock-In Thermography (HS-LIT), which visualizes the positive feedback effect. In this paper, we present a modified HS-LIT technique that allows us to quantify directly a loop-gain for hot-spot formation. By quantifying the loop-gain we obtain a direct measure of how unstable a local hot-spot is, which allows the non-destructive study of hot-spot formation under various conditions and in various cells and cell types. We discuss the modified HS-LIT setup for the direct measurement of the loop-gain. Furthermore, we demonstrate the new method by measuring the loop-gain of the thermal runaway effect in a CIGS solar cell as a function of reverse bias voltage.
Key words: Reverse bias damage / hot-spot / CIGS thin-films / thermal runaway / lock-in thermography
© S. Nofal et al., Published by EDP Sciences, 2023
This is an Open Access article distributed under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.