Performance of silver contacts in III-V solar cells
Fihlman, Antti (2022)
2022
Materiaalitekniikan DI-ohjelma - Master's Programme in Materials Engineering
Tekniikan ja luonnontieteiden tiedekunta - Faculty of Engineering and Natural Sciences
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Hyväksymispäivämäärä
2022-03-18
Julkaisun pysyvä osoite on
https://urn.fi/URN:NBN:fi:tuni-202202182048
https://urn.fi/URN:NBN:fi:tuni-202202182048
Tiivistelmä
The development of solar cells with higher efficiencies is paramount when future global energy demands are to be met with renewable energy sources. The largest efficiency has been achieved with a multijunction solar cell manufactured from group III-V semiconductors. In order to improve the cells efficiency parasitic power losses manifesting in the cell should be reduced. This can be done by reducing the series resistance of the front metal contact.
The aim for this thesis was to fabricate solar cells with smaller series resistances by changing the conductive metal in the front contact from gold to a silver-based structure. Silver has higher conductivity when compared to gold and it is also cheaper with a downside of being less chemically stable. This material change was studied in three different experiments which measured the properties of the fabricated silver such as conductivity, chemical stability and overall functionality in the process. In addition to the tests for the material properties multiple CPV solar cells with silver contacts were fabricated and their performance was compared to identical solar cells with gold contacts.
The material tests proved that the silver-based structure is workable in the fabrication process and its conductivity was higher than gold. The performance of the fabricated silver cells was satisfactory, and it was identical to the gold cells when their performance was measured with a solar simulator in concentrations of 1, 100, 250, 500, 750 and 900 suns. However, when subjected to a high-power laser performance test it was observed that the silver cells had more resistive losses than the gold ones. The reason for performance decrease was estimated to be related to chemical degradation of silver during the manufacturing process as the structure was not completely protected.
However, future developments for the silver contacts seem quite promising and with some adjustments to the fabrication process the contact structure could be protected from degradation. This could be done by utilizing alternative etchants which won’t react with the silver structure or utilizing a metallization process that covers the silver contact from its’ sides where it is most vulnerable for process chemicals. In conclusion, this thesis answered all the research questions provided sufficiently and it could function as a base for further silver contact development in III-V solar cells.
The aim for this thesis was to fabricate solar cells with smaller series resistances by changing the conductive metal in the front contact from gold to a silver-based structure. Silver has higher conductivity when compared to gold and it is also cheaper with a downside of being less chemically stable. This material change was studied in three different experiments which measured the properties of the fabricated silver such as conductivity, chemical stability and overall functionality in the process. In addition to the tests for the material properties multiple CPV solar cells with silver contacts were fabricated and their performance was compared to identical solar cells with gold contacts.
The material tests proved that the silver-based structure is workable in the fabrication process and its conductivity was higher than gold. The performance of the fabricated silver cells was satisfactory, and it was identical to the gold cells when their performance was measured with a solar simulator in concentrations of 1, 100, 250, 500, 750 and 900 suns. However, when subjected to a high-power laser performance test it was observed that the silver cells had more resistive losses than the gold ones. The reason for performance decrease was estimated to be related to chemical degradation of silver during the manufacturing process as the structure was not completely protected.
However, future developments for the silver contacts seem quite promising and with some adjustments to the fabrication process the contact structure could be protected from degradation. This could be done by utilizing alternative etchants which won’t react with the silver structure or utilizing a metallization process that covers the silver contact from its’ sides where it is most vulnerable for process chemicals. In conclusion, this thesis answered all the research questions provided sufficiently and it could function as a base for further silver contact development in III-V solar cells.