For none, one, or two polarities

How do POLO junctions fit best into industrial Si solar cells?

authored by: Robby Peibst, Christian Kruse, Sören Schäfer, Verena Mertens, Stefan Bordihn, Thorsten Dullweber, Felix Haase, Christina Hollemann, Bianca Lim, Byungsul Min, Raphael Niepelt, Henning Schulte-Huxel, Rolf Brendel
Abstract: We present a systematic study on the benefit of the implementation of poly-Si on oxide (POLO) or related junctions into p-type industrial Si solar cells as compared with the benchmark of Passivated Emitter and Rear Cell (PERC). We assess three aspects: (a) the simulated efficiency potential of representative structures with POLO junctions for none (=PERC+), one, and for two polarities; (b) possible lean process flows for their fabrication; and (c) experimental results on major building blocks. Synergistic efficiency gain analysis reveals that the exclusive suppression of the contact recombination for one polarity by POLO only yields moderate efficiency improvements between 0.23%_abs and 0.41%_abs as compared with PERC+ because of the remaining recombination paths. This problem is solved in a structure that includes POLO junctions for both polarities (POLO²), for whose realization we propose a lean process flow, and for which we experimentally demonstrate the most important building blocks. However, two experimental challenges—alignment tolerances and screen-print metallization of p+ poly-Si—are unsolved so far and reduced the efficiency of the “real” POLO² cell as compared with an idealized scenario. As an intermediate step, we therefore work on a POLO IBC cell with POLO junctions for one polarity. It avoids the abovementioned challenges of the POLO² structure, can be realized within a lean process flow, and has an efficiency benefit of 1.59%_abs as compared with PERC—because not only contact recombination is suppressed but also the entire phosphorus emitter is replaced by an n+ POLO junction.
Organisation(s): Institute of Electronic Materials and Devices
Solar Energy Section
External Organisation(s): Institute for Solar Energy Research (ISFH)
Type: Article
Journal: Progress in Photovoltaics: Research and Applications
Volume: 28
Pages: 503-516
No. of pages: 14
ISSN: 1062-7995
Publication date: 20.05.2020
Publication status: Published
Peer reviewed: Yes
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Renewable Energy, Sustainability and the Environment, Condensed Matter Physics, Electrical and Electronic Engineering
Sustainable Development Goals: SDG 7 - Affordable and Clean Energy
Electronic version(s): https://doi.org/10.1002/pip.3201 (Access: Open)