Lithium Fluoride Based Electron Contacts for High Efficiency n-Type Crystalline Silicon Solar Cells

James Bullock, Peiting Zheng, Quentin Jeangros, Mahmut Tosun, Mark Hettick, Carolin M. Sutter-Fella, Yimao Wan, Thomas Allen, Di Yan, Daniel Macdonald, Stefaan De Wolf, Aïcha Hessler-Wyser, Andres Cuevas*, Ali Javey

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

119 Scopus citations


Low-resistance contact to lightly doped n-type crystalline silicon (c-Si) has long been recognized as technologically challenging due to the pervasive Fermi-level pinning effect. This has hindered the development of certain devices such as n-type c-Si solar cells made with partial rear contacts (PRC) directly to the lowly doped c-Si wafer. Here, a simple and robust process is demonstrated for achieving mΩ cm2 scale contact resistivities on lightly doped n-type c-Si via a lithium fluoride/aluminum contact. The realization of this low-resistance contact enables the fabrication of a first-of-its-kind high-efficiency n-type PRC solar cell. The electron contact of this cell is made to less than 1% of the rear surface area, reducing the impact of contact recombination and optical losses, permitting a power conversion efficiency of greater than 20% in the initial proof-of-concept stage. The implementation of the LiFx/Al contact mitigates the need for the costly high-temperature phosphorus diffusion, typically implemented in such a cell design to nullify the issue of Fermi level pinning at the electron contact. The timing of this demonstration is significant, given the ongoing transition from p-type to n-type c-Si solar cell architectures, together with the increased adoption of advanced PRC device structures within the c-Si photovoltaic industry.

Original languageEnglish (US)
Article number1600241
JournalAdvanced Energy Materials
Issue number14
StatePublished - Jul 20 2016

Bibliographical note

Funding Information:
J.B. and P.Z. contributed equally to this work. Device design, fabrication, and characterization were funded by the Bay Area Photovoltaics Consortium (BAPVC) and the Australian Renewable Energy Agency (ARENA). Materials characterization was supported by the Electronic Materials Programs, funded by the Director, Office of Science, Office of Basic Energy Sciences, Material Sciences and Engineering Division of the U.S. Department of Energy under (Contract No. DE-AC02-05CH11231). Work at the Molecular Foundry was supported by the Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231. Work at EPFL was supported by the Office Fedéral de l'Energie (OFEN) and the Interdisciplinary Centre for Electron Microscopy (CIME) of EPFL is acknowledged for access to their electron microscopes. C.M.S.-F. acknowledges financial support from the Swiss National Science Foundation (P2EZP2_155586).

Publisher Copyright:
© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim


  • contacts
  • fermi levels
  • lithium fluoride
  • photovoltaics
  • silicon solar cells

ASJC Scopus subject areas

  • Renewable Energy, Sustainability and the Environment
  • Materials Science(all)


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