Characterization of metallization-induced recombination losses of screen-printed silicon solar cells

Abstract: This thesis investigates metallization-induced recombination losses in silicon solar cells, with a focus on screen-printed silver (Ag) fire-through metallization. Recombination losses at the metallization of silicon solar cells are detrimental for the performance of a solar cell and can limit the conversion efficiency.
For the precise determination of the recombination current density in the metallized areas (j0,met), an approach based on numerical simulations is refined during this work and the results are compared to an area-weighted approach commonly used in literature. Thereby, an underestimation of j0,met by up to 30% is observed, using the area-weighted approach compared to the results using the approach based on numerical simulations. Such an underestimation is confirmed to be physically expected, due to the implicit assumption of a uniform excess carrier density Δn in the entire sample by the area-weighted approach. Furthermore, the degree of underestimation is found to be a function of sample characteristics as especially base resistivity, finger distance or j0,met itself.
To further increase the accuracy of the approach based on numerical simulations, an interpolation scheme is developed, which predicts the photoluminescence signal in a metallized region, if it was virtually non-metallized, with a standard deviation of σ ≈ 0.7% for the investigated samples. This is a factor of four lower than for state-of-the-art approaches. Thereby, j0,met results are determined with a total uncertainty between 15% to 18% and an average statistical scattering (σ) between 5% to 6%, respectively.
The resulting local j0,met values are then correlated to varying local sample characteristics on one wafer, as the emitter sheet resistance, the peak wafer temperature during contact firing measured via infrared thermal imaging and the finger distance. By decreasing the finger distance d from d = 1000 μm to d = 200 μm, j0,met decreases by up to 18% for the investigated samples, which is resolvable due to the increased accuracy achieved in this work.
Finally, j0,met is modelled based on a comprehensive local microstructure analysis of the interface between metallization and phosphorus emitter, and the local emitter doping profile. Comparing modelled and measured j0,met results reveals that in most cases recombination is dominantly induced due to the etching of the passivation and into the phosphorus emitter by the
metallization paste. However, for Ag crystallites protruding deep into the emitter or rather beyond the junction, recombination at crystallites becomes significant as well. Additionally, the results indicate that the etch depth into the emitter is sensitive to the doping profile itself.
Altogether, this work improves the accuracy as well as the understanding of the characterization of metallization-induced recombination losses of silicon solar cells. Moreover, the results extend the knowledge of the microstructural origin of the losses, and the interaction between metallization paste and highly-doped emitter during contact firing

Angaben zum Objekt

• Standort: Deutsche Nationalbibliothek Frankfurt am Main
• Umfang: Online-Ressource
• Sprache: Englisch
• Anmerkungen: Universität Freiburg, Dissertation, 2021

Klassifikation und Themen

• Klassifikation: Elektrotechnik, Elektronik
• Schlagwort: Silicon solar cells ; Metallizing

Beteiligte, Orts- und Zeitangaben

• Ereignis: Veröffentlichung
• (wo): Freiburg
• (wer): Universität
• (wann): 2021
• Urheber: Herrmann, David
• Beteiligte Personen und Organisationen: Glunz, Stefan ; Altermatt, Pietro P. ; Fraunhofer-Institut für Solare Energiesysteme ; Albert-Ludwigs-Universität Freiburg. Fakultät für Angewandte Wissenschaften

Weitere Informationen

• DOI: 10.6094/UNIFR/222718
• URN: urn:nbn:de:bsz:25-freidok-2227182
• Rechteinformation: Kein Open Access; Der Zugriff auf das Objekt ist unbeschränkt möglich.
• Letzte Aktualisierung: 25.03.2025, 13:44 MEZ