The influence of hydrogen on silicon solar cells: investigating the link to degradation mechanisms

Abstract: Hydrogen has been welcomed and artificially introduced into silicon solar cells due to its beneficial property of passivating defects, thus enhancing the material quality. However, hydrogen has also been found to be related to a degradation of power conversion efficiency, termed light- and elevated-temperature-induced degradation (LeTID), which is one of the main challenges for silicon solar cells. This work aims at understanding the mechanisms of hydrogen, particular its role in the degradation of solar cells, to ideally maintain the positive and prevent the negative effects of hydrogen. To this end, samples are manufactured using industrially relevant processes and investigated at elevated temperatures in the dark and under illumination. Hydrogen is studied with a combination of resistivity-based measurements and Fourier-transfrom infrared (FT-IR) spectroscopy. A special sample design is used to study the hydrogen kinetics in parallel to effective charge carrier lifetime measurements, which is used for the investigation of degradation phenomena.
First, the kinetics of hydrogen are investigated under those conditions. Insights into the manifold interactions of the different complexes are gained, encompassing differently charged atomic hydrogen (H+, H– , H0), hydrogen molecules (H2), boron atoms, boron-hydrogen (BH) pairs, and further, unknown complexes. Differences between dark and illuminated studies are observed and a theoretical model is developed. This model is able to describe the observed experimental behavior in thermal equilibrium and serves as a basis for the other investigations of this work.
Secondly, the introduction of hydrogen into solar cells and different manipulation pathways are discussed, which occurs through the in-diffusion of hydrogen from silicon nitride (SiNx) layers into the silicon bulk during the fast-firing process. Both processes and their influence on the final hydrogen concentration are investigated. A special focus lies on the cooling ramp, which is shown to lead to the out-diffusion of hydrogen at temperatures below ≈ 700 °C, with a stronger out-diffusion at higher temperatures.
The final focus lies on the role of hydrogen in two degradation phenomena, LeTID and surface related degradation (SRD). By correlating the characteristics and kinetics of LeTID and SRD with the hydrogen kinetics, insights into the possible interactions are gained. This results in the proposition of a reaction that includes the LeTID defect states alongside the other occurring hydrogen-related reaction. It is found that molecular hydrogen (H2) plays an important role in the formation of the LeTID defect, while the regeneration is suggested to occur through atomic hydrogen passivating the defect. Furthermore, the experimental results indicate that hydrogen diffuses towards the surface, resulting in the observed degradation of surface passivation. It is proposed that this is due to the formation of surface-near, recombination-active hydrogen platelets.

This work presents the first in-depth investigations of the kinetics of hydrogen in solar cell-like samples, particularly in the context of two degradation phenomena, LeTID and SRD. Diversely processed samples studied under various operating conditions lead to a series of effects, culminating in the proposition of a theory on the relationship between the different hydrogen complexes and states, and the observed degradation phenomena. The results show that the degradation phenomena cannot be interpreted without the context of hydrogen and that it is imperative to understand the mechanisms of hydrogen if one wants to understand the mechanism of these degradation phenomena. By understanding the link between hydrogen and the degradation mechanisms, it is possible to develop strategies to prevent the occurrence of those degradation phenomena, leading ultimately to more long-term-stable silicon solar cells

Angaben zum Objekt

• Standort: Deutsche Nationalbibliothek Frankfurt am Main
• Umfang: Online-Ressource
• Sprache: Englisch
• Anmerkungen: Universität Freiburg, Dissertation, 2024

Klassifikation und Themen

• Schlagwort: Silicium ; Wasserstoff ; Solarzelle ; Degradation ; Rekombination ; Passivierung

Beteiligte, Orts- und Zeitangaben

• Ereignis: Veröffentlichung
• (wo): Freiburg
• (wer): Universität
• (wann): 2024
• Urheber: Hammann, Benjamin
• Beteiligte Personen und Organisationen: Glunz, Stefan ; Glunz, Stefan ; Schmidt, Jan ; Albert-Ludwigs-Universität Freiburg. Fakultät für Angewandte Wissenschaften

Weitere Informationen

• DOI: 10.6094/UNIFR/246916
• URN: urn:nbn:de:bsz:25-freidok-2469165
• Rechteinformation: Open Access; Der Zugriff auf das Objekt ist unbeschränkt möglich.
• Letzte Aktualisierung: 25.03.2025, 13:53 MEZ