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

Saman Sharbaf Kalaghichi (), Jan Hoß, Jonathan Linke, Stefan Lange and Jürgen H. Werner
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Saman Sharbaf Kalaghichi: International Solar Energy Research Center Konstanz, Rudolf-Diesel-Straße 15, 78467 Konstanz, Germany
Jan Hoß: International Solar Energy Research Center Konstanz, Rudolf-Diesel-Straße 15, 78467 Konstanz, Germany
Jonathan Linke: International Solar Energy Research Center Konstanz, Rudolf-Diesel-Straße 15, 78467 Konstanz, Germany
Stefan Lange: Fraunhofer Center for Silicon Photovoltaics, Otto-Eißfeldt-Straße 12, 06120 Halle, Germany
Jürgen H. Werner: Institute for Photovoltaics, University of Stuttgart, Pfaffenwaldring 47, 70569 Stuttgart, Germany

Energies, 2024, vol. 17, issue 6, 1-14

Abstract: Crystalline silicon (c-Si) solar cells with passivation stacks consisting of a polycrystalline silicon (poly-Si) layer and a thin interfacial silicon dioxide (SiO 2 ) 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 SiN x :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 t anneal = 30 min and an annealing temperature 600 °C ≤ T anneal ≤ 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 re activation 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 T anneal = 985 °C, the reactivated layers show high sheet conductance ( G sh ) with G sh = 24 mS sq and high passivation quality, with the implied open-circuit voltage ( iV OC ) reaching iV OC = 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/SiO 2 contact passivation layers.

Keywords: passivating contacts; poly-Si layers; laser activation; thermal stability; electrical deactivation; reactivation (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2024
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