Utilization of Tabula Rasa to Stabilize Bulk Lifetimes in n-Cz Silicon for High-Performance Solar Cell Processing

Vincenzo LaSalvia, Pauls Stradins, William Nemeth, Matthew Page, Tonio Buonassisi, Amanda Youssef, Mallory Jensen

Research output: Contribution to conferencePaperpeer-review

4 Scopus Citations


We investigate a high temperature, high cooling-rate anneal Tabula Rasa (TR) and report its implications on n-type Czochralski-grown silicon (n-Cz Si) for photovoltaic fabrication. Tabula Rasa aims at dissolving and homogenizing oxygen precipitate nuclei that can grow during the cell process steps and degrade the cell performance due to their high internal gettering and recombination activity. The Tabula Rasa thermal treatment is performed in a clean tube furnace with cooling rates >100°C/s. We characterize the bulk lifetime by Sinton lifetime and photoluminescence mapping just after Tabula Rasa, and after the subsequent cell processing. After TR, the bulk lifetime surprisingly degrades to < 0.1ms, only to recover to values equal or higher than the initial non-treated wafer (several ms), after typical high temperature cell process steps. Those include boron diffusion and oxidation; phosphorus diffusion/oxidation; ambient annealing at 850°C; and crystallization annealing of tunneling-passivating contacts (doped polycrystalline silicon on 1.5 nm thermal oxide). The drastic lifetime improvement during high temperature cell processing is attributed to improved external gettering of metal impurities and annealing of intrinsic point defects. Time and injection dependent lifetime spectroscopy further reveals the mechanisms of lifetime improvement after Tabula Rasa treatment. Additionally, we report the efficacy of Tabula Rasa on n-type Cz-Si wafers and its dependence on oxygen concentration, correlated to position within the ingot.

Original languageAmerican English
Number of pages4
StatePublished - 18 Nov 2016
Event43rd IEEE Photovoltaic Specialists Conference, PVSC 2016 - Portland, United States
Duration: 5 Jun 201610 Jun 2016


Conference43rd IEEE Photovoltaic Specialists Conference, PVSC 2016
Country/TerritoryUnited States

Bibliographical note

Publisher Copyright:
© 2016 IEEE.

NREL Publication Number

  • NREL/CP-5J00-65794


  • Cz silicon
  • oxygen precipitation
  • photovoltaics
  • silicon
  • solar cells


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