Passivation Enhancement of Poly-Si Carrier-Selective Contacts by Applying ALD Al_2O_3 Capping Layers

Guangtao Yang, Bas Van de Loo, Maciej Stodolny, Gianluca Limodio, Jimmy Melskens, Olindo Isabella, Arthur Weeber, Miro Zeman, W. M.M. Kessels, More Authors

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Abstract

Hydrogenation of polycrystalline silicon (poly-Si) passivating contacts is crucial for maximizing their passivation performance. This work presents the application of Al2O3 prepared by atomic layer deposition as a hydrogenating capping layer. Several important questions related to this application of Al2O3 are addressed by comparing results from Al2O3 single layers, SiNx single layers, and Al2O3/SiNx double layers to different poly-Si types. We investigate the effect of the Al2O3 thickness, the poly-Si thickness, the poly-Si doping type, and the postdeposition annealing treatment on the passivation quality of poly-Si passivating contacts. Especially, the Al2O3/SiNx stack greatly enhances the passivation quality of both n+ and p+ doped as well as intrinsic poly-Si layers. The Al2O3 layer thickness is crucial for the single-layer approach, whereas the Al2O3/SiNx stack is less sensitive to the thickness of the Al2O3 layer. A thicker Al2O3 layer is needed for effectively hydrogenating p+ compared to n+ poly-Si passivating contact. The capping layers can hydrogenate poly-Si layers with thicknesses up to at least 600 nm. The hydrogenation-enhanced passivation for n+ poly-Si is found to be more thermally stable in comparison to p+ poly-Si. These results provide guidelines on the use of Al2O3 capping layers for poly-Si contacts to significantly improve their passivation performance.

Original languageEnglish
Pages (from-to)259-266
Number of pages8
JournalIEEE Journal of Photovoltaics
Volume12
Issue number1
DOIs
Publication statusPublished - 2021

Keywords

  • Atomic layer deposition (ALD) Al2O3
  • hydrogenation
  • passivation quality
  • polycrystalline silicon (poly-Si) passivating contacts
  • thermal stability

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