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Evolution of the surface passivation mechanism during the fabrication of ex-situ doped poly-Si(B)/SiOx passivating contacts for high-efficiency c-Si solar cells

Abstract : Passivating the contacts of crystalline silicon (c-Si) solar cells (SC) with a poly-crystalline silicon (poly-Si) layer on top of a thin silicon oxide (SiOx) is currently sparking interest for reducing carrier recombination at the interface between the metal electrode and the c-Si substrate. However, due to the interrelation between different mechanisms at play, a comprehensive understanding of the surface passivation provided by the poly-Si/SiOx contact in the final SC has not been achieved yet. In the present work, we report on an original ex-situ doping process of the poly-Si layer through the deposition of a B-rich dielectric layer followed by an annealing step to diffuse B dopants in the layer. We propose an in-depth investigation of the passivation scheme of the resulting B-doped poly-Si/SiOx contact by first comparing the surface passivation provided by ex-situ doped and intrinsic poly-Si/SiOx contacts at different steps of the fabrication process. The excellent surface passivation properties obtained with the ex-situ doped poly-Si(B) contact (iVoc = 733 mV and J0 = 6.1 fA cm−2) attests to the good quality of this contact. We then propose further STEM, ECV and ToF-SIMS characterizations to assess: i) the evolution of the microstructure and B-doping profile through ex-situ doping and ii) the diffusion profile of hydrogen in the poly-Si contact. Our results show a gradual filling of the poly-Si layer with active B dopants with increasing annealing temperature (Ta), which strengthens the field-effect passivation and enables an iVoc increase after annealing up to 800 °C. We also observe a diffusion of O from the SiON:B doping layer to the interfacial SiOx layer during annealing, that likely enhances the passivation stability of our ex-situ doped poly-Si contact with increasing Ta. Finally, we conclude that the mechanism dominating the surface passivation changes during the fabrication process of the poly-Si/SiOx contact from field-effect passivation after annealing (performed for B-diffusion in the contact) to chemical passivation after following hydrogenation of the samples (performed by depositing a H-rich silicon nitride layer)
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https://hal.archives-ouvertes.fr/hal-03288976
Contributor : Jean-Paul Kleider <>
Submitted on : Thursday, August 5, 2021 - 5:57:21 PM
Last modification on : Tuesday, August 24, 2021 - 2:02:44 PM

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Audrey Morisset, Raphaël Cabal, Valentin Giglia, Adrien Boulineau, Eric de Vito, et al.. Evolution of the surface passivation mechanism during the fabrication of ex-situ doped poly-Si(B)/SiOx passivating contacts for high-efficiency c-Si solar cells. Solar Energy Materials and Solar Cells, Elsevier, 2021, 221, pp.110899. ⟨10.1016/j.solmat.2020.110899⟩. ⟨hal-03288976⟩

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