Public update iPrecise 2022:
The iPrecise project aims at developing the technologies for the next generation of c-Si solar cells following the current industrial mainstream “PERC” structure. The main focus of the project consists in the integration of passivating contacts based on a polycrystalline silicon (poly-Si) layer on top of a very thin silicon oxide (SiOx ~1-2 nm) in between the crystalline silicon (c-Si) absorber and the metal contacts. In 2022, the passivation and charge collection of poly-Si contacts fabricated either by PECVD or PVD and compatible with the current industrial metallization process were improved. The integration of poly-Si contacts at the front of c-Si solar cells requires a patterning of the poly-Si layer, such that most of the surface is with a thin layer to ensure low parasitic absorption and a higher layer thickness is used below the metal contacts. In the frame of iPrecise, a first patterning sequence based on the use of a hard mask during deposition of the poly-Si layer was developed. This method was used to fabricate proof-of-concept c-Si solar cells with a patterned poly-Si layer at the front, resulting in conversion efficiencies up to 21.7%. This represents the best demonstration reported in the literature so far, however, the deposition rate of the poly-Si layer is decreased within the narrow mask openings, which represents a limit towards industrial transfer of this process. Thus, we are developing an alternative patterning process better adapted for a transfer to the industry, which consists in the full area deposition of a thick poly-Si layer followed by selective wet etching. The main challenge here is to maintain a good surface passivation while etching the poly-Si layer as thin as possible between the metal contacts. The optimization of the poly-Si layer composition and the wet etching process enabled us to demonstrate a controlled etching of the poly-Si layer while preserving the surface passivation underneath. Finally, we developed large-area TOPCon solar cells integrating a PVD based poly-Si contacts at the rear side. Thanks to the optimizations of the tunnel oxide and plasma assisted ex-situ doped poly-Si layer, c-Si solar cells with efficiencies up to 22.8% were demonstrated.
Morisset, A., Famprikis, T., Haug, F. J., Ingenito, A., Ballif, C., & Bannenberg, L. J. In Situ Reflectometry and Diffraction Investigation of the Multiscale Structure of p-Type Polysilicon Passivating Contacts for c-Si Solar Cells. ACS applied materials & interfaces, 14(14), 2022, 16413–16423. https://doi.org/10.1021/acsami.2c01225
F.-J. Haug, S. Libraro, M. Lehmann, A. Morisset, A. Ingenito, C. Ballif
Impact of rapid thermal processing on bulk and surface recombination mechanisms in FZ silicon with fired passivating contacts, Solar Energy Materials and Solar Cells, Volume 238, 2022, 111647, https://doi.org/10.1016/j.solmat.2022.111647
Poster at 19th Swiss National Photovoltaic Conference, 1/2 July 2021, Bern
Localisation of front side passivating contacts for direct metallisation of high-efficiency c-Si solar cells, F. Meyer, A. Ingenito, J. J. Diaz Leon, X. Niquillea, C. Allebé, S. Nicolay, F.-J. Haug, C. Ballif, https://www.swissolar.ch/fileadmin/user_upload/Tagungen/PV-Tagung_2021/2_Poster_FM.pdf