Influence of the annealing temperature of (n) poly-Si/SiOx passivating contacts on their firing stability

Linke, Jonathan; Hoß, J.; Buchholz, Florian; Lossen, J.; Kopecek, Radovan

doi:10.1016/j.solmat.2023.112415

Solar Energy Materials and Solar Cells

2023

DOI: 10.1016/j.solmat.2023.112415

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Influence of the annealing temperature of (n) poly-Si/SiOx passivating contacts on their firing stability

Jonathan Linke

J. Hoß

Florian Buchholz

et al.

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2024

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Cited by 4 publications

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“…• Maskless and, consequently, low-cost patterning: Highly boron-doped p ++ -poly-Si layers provide the necessary etch stop in an alkaline solution such as potassium hydroxide (KOH) [15]. We currently use this feature for the production of advanced passivated contact cells with selective p ++ -poly-Si layers [16,17].…”

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confidence: 99%

Three-Step Process for Efficient Solar Cells with Boron-Doped Passivated Contacts

Sharbaf Kalaghichi,

Hoß,

Linke

et al. 2024

Energies

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Crystalline silicon (c-Si) solar cells with passivation stacks consisting of a polycrystalline silicon (poly-Si) layer and a thin interfacial silicon dioxide (SiO2) layer show high conversion efficiencies. Since the poly-Si layer in this structure acts as a carrier transport layer, high doping of the poly-Si layer is crucial for high conductivity and the efficient transport of charge carriers from the bulk to a metal contact. In this respect, conventional furnace-based high-temperature doping methods are limited by the solid solubility of the dopants in silicon. This limitation particularly affects p-type doping using boron. Previously, we showed that laser activation overcomes this limitation by melting the poly-Si layer, resulting in an active concentration beyond the solubility limit after crystallization. High electrically active boron concentrations ensure low contact resistivity at the (contact) metal/semiconductor interface and allow for the maskless patterning of the poly-Si layer by providing an etch-stop layer in an alkaline solution. However, the high doping concentration degrades during long high-temperature annealing steps. Here, we performed a test of the stability of such a high doping concentration under thermal stress. The active boron concentration shows only a minor reduction during SiNx:H deposition at a moderate temperature and a fast-firing step at a high temperature and with a short exposure time. However, for an annealing time tanneal = 30 min and an annealing temperature 600 °C ≤ Tanneal≤ 1000 °C, the high conductivity is significantly reduced, whereas a high passivation quality requires annealing in this range. We resolve this dilemma by introducing a second, healing laser reactivation step, which re-establishes the original high conductivity of the boron-doped poly-Si and does not degrade the passivation. After a thermal annealing temperature Tanneal = 985 °C, the reactivated layers show high sheet conductance (Gsh) with Gsh = 24 mS sq and high passivation quality, with the implied open-circuit voltage (iVOC) reaching iVOC = 715 mV. Therefore, our novel three-step process consisting of laser activation, thermal annealing, and laser reactivation/healing is suitable for fabricating highly efficient solar cells with p++-poly-Si/SiO2 contact passivation layers.

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mentioning

confidence: 99%

Three-Step Process for Efficient Solar Cells with Boron-Doped Passivated Contacts

Sharbaf Kalaghichi,

Hoß,

Linke

et al. 2024

Energies

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Ultrafast laser-annealing of hydrogenated amorphous silicon in tunnel oxide passivated contacts for high-efficiency n-type silicon solar cells

Zhou,

Su,

Zhang

et al. 2024

Materials Today Energy

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Current status and challenges for hole-selective poly-silicon based passivating contacts

Basnet,

Yan,

Kang

et al. 2024

Applied Physics Reviews

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Doped polysilicon (poly-Si) passivating contacts have emerged as a key technology for the next generation of silicon solar cells in mass production, owing to their excellent performance and high compatibility with the existing passivated emitter and rear cell technology. However, the current solar cell architecture based on a rear-side electron-selective (n+) poly-Si contact is also approaching its practical limit (∼26%) in mass production. The full potential of doped poly-Si passivating contacts can only be realized through incorporation of both electron-selective and hole-selective (p+) poly-Si contacts. While studies of both p+ and n+ poly-Si contacts commenced simultaneously, significant performance differences have arisen. Phosphorus-doped poly-Si contacts consistently outperform boron-doped counterparts, displaying typically lower recombination current density (J0) values (1–5fA/cm2 vs 7–15fA/cm2). This discrepancy can be attributed to inadequate optimization of p+ poly-Si contacts and fundamental limitations related to boron doping. The poorer passivation of p+ poly-Si contacts can be at least partly attributed to boron segregation into the interfacial oxide layers, compromising the interfacial oxide integrity and reducing the chemical passivation effectiveness. This review critically examines the progress of p+ poly-Si contacts characterized by cell efficiency and J0 values, delves into existing challenges, identifies potential solutions, and explores some potential solar cell architectures to enhance efficiency by incorporating p+ poly-Si contacts.

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Influence of the annealing temperature of (n) poly-Si/SiOx passivating contacts on their firing stability

Cited by 4 publications

References 12 publications

Three-Step Process for Efficient Solar Cells with Boron-Doped Passivated Contacts

Three-Step Process for Efficient Solar Cells with Boron-Doped Passivated Contacts

Ultrafast laser-annealing of hydrogenated amorphous silicon in tunnel oxide passivated contacts for high-efficiency n-type silicon solar cells

Current status and challenges for hole-selective poly-silicon based passivating contacts

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