Dissertation in the field of Semiconductor Technology, Päivikki Repo

”Reducing surface recombination in black silicon photovoltaic devices using atomic layer deposition”

This thesis focuses on the reduction of two eminent losses in silicon solar cells: surface recombination and surface reflectance. Surface recombination decreases the collection probability of charge carriers and can lead to significant drop in solar cell efficiency. The reduction of this detrimental effect is addressed in this work by passivating the surface with different atomic layer deposited (ALD) thin film coatings and in general good surface passivation is reached in all cases.

Surface passivation becomes even more important in the case of black silicon (b-Si), i.e. nanostructured silicon surface, where the large surface area results in high surface recombination velocity. Black silicon itself has gained much interest es-pecially for photovoltaic applications due to its low surface reflectance on a wide spectral range and acceptance angle. However, the increase in the surface re-combination has always hindered the application of b-Si e.g. in solar cells. This work presents that ALD Al2O3 can solve this issue by providing completely con-formal coating and excellent passivation also on nanostructured surfaces. This proves the potential of using the combination of black silicon and ALD Al2O3 in different photovoltaic devices. Laboratory scale solar cells fabricated in this thesis have shown good performance and with more process optimization even better could be expected. Also, there is a great promise to bring black silicon from the lab to industry in the near future due to its strong resilience to multiple processing steps demonstrated in this work.

Opponent: Professor Stefan Glunz, University of Freiburg, Germany

Supervisor: Professor Hele Savin, Aalto University School of Electrical Engineering, Department of Micro- and Nanosciences

Dissertation website

Contact information:
Päivikki Repo
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paivikki.repo@aalto.fi