Three-Step Process for Efficient Solar Cells with Boron-Doped Passivated Contacts
Crystalline silicon (c-Si) solar cells with passivation stacks consisting of a polycrystalline silicon (poly-Si) layer and a thin interfacial silicon dioxide (SiO<sub>2</sub>) layer show high conversion efficiencies. Since the poly-Si layer in this structure acts as a carrier transport l...
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MDPI AG
2024-03-01
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| Online Access: | https://www.mdpi.com/1996-1073/17/6/1319 |
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| author | Saman Sharbaf Kalaghichi Jan Hoß Jonathan Linke Stefan Lange Jürgen H. Werner |
| author_facet | Saman Sharbaf Kalaghichi Jan Hoß Jonathan Linke Stefan Lange Jürgen H. Werner |
| author_sort | Saman Sharbaf Kalaghichi |
| collection | DOAJ |
| description | Crystalline silicon (c-Si) solar cells with passivation stacks consisting of a polycrystalline silicon (poly-Si) layer and a thin interfacial silicon dioxide (SiO<sub>2</sub>) 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<sub>x</sub>: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 <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><msub><mi>t</mi><mrow><mi>anneal</mi></mrow></msub></semantics></math></inline-formula> = 30 min and an annealing temperature 600 °C ≤ <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><msub><mi>T</mi><mrow><mi>anneal</mi></mrow></msub></semantics></math></inline-formula>≤ 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 <i>re</i>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 <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><msub><mi>T</mi><mrow><mi>anneal</mi></mrow></msub></semantics></math></inline-formula> = 985 °C, the reactivated layers show high sheet conductance (<i>G<sub>sh</sub></i>) with <i>G<sub>sh</sub></i> = 24 mS sq and high passivation quality, with the implied open-circuit voltage (<i>iV<sub>OC</sub></i>) reaching <i>iV<sub>OC</sub></i> = 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<sup>++</sup>-poly-Si/SiO<sub>2</sub> contact passivation layers. |
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| series | Energies |
| spelling | doaj.art-4bec127314564c85a1952d06f6efff942024-03-27T13:35:26ZengMDPI AGEnergies1996-10732024-03-01176131910.3390/en17061319Three-Step Process for Efficient Solar Cells with Boron-Doped Passivated ContactsSaman Sharbaf Kalaghichi0Jan Hoß1Jonathan Linke2Stefan Lange3Jürgen H. Werner4International Solar Energy Research Center Konstanz, Rudolf-Diesel-Straße 15, 78467 Konstanz, GermanyInternational Solar Energy Research Center Konstanz, Rudolf-Diesel-Straße 15, 78467 Konstanz, GermanyInternational Solar Energy Research Center Konstanz, Rudolf-Diesel-Straße 15, 78467 Konstanz, GermanyFraunhofer Center for Silicon Photovoltaics, Otto-Eißfeldt-Straße 12, 06120 Halle, GermanyInstitute for Photovoltaics, University of Stuttgart, Pfaffenwaldring 47, 70569 Stuttgart, GermanyCrystalline silicon (c-Si) solar cells with passivation stacks consisting of a polycrystalline silicon (poly-Si) layer and a thin interfacial silicon dioxide (SiO<sub>2</sub>) 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<sub>x</sub>: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 <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><msub><mi>t</mi><mrow><mi>anneal</mi></mrow></msub></semantics></math></inline-formula> = 30 min and an annealing temperature 600 °C ≤ <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><msub><mi>T</mi><mrow><mi>anneal</mi></mrow></msub></semantics></math></inline-formula>≤ 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 <i>re</i>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 <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><msub><mi>T</mi><mrow><mi>anneal</mi></mrow></msub></semantics></math></inline-formula> = 985 °C, the reactivated layers show high sheet conductance (<i>G<sub>sh</sub></i>) with <i>G<sub>sh</sub></i> = 24 mS sq and high passivation quality, with the implied open-circuit voltage (<i>iV<sub>OC</sub></i>) reaching <i>iV<sub>OC</sub></i> = 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<sup>++</sup>-poly-Si/SiO<sub>2</sub> contact passivation layers.https://www.mdpi.com/1996-1073/17/6/1319passivating contactspoly-Si layerslaser activationthermal stabilityelectrical deactivationreactivation |
| spellingShingle | Saman Sharbaf Kalaghichi Jan Hoß Jonathan Linke Stefan Lange Jürgen H. Werner Three-Step Process for Efficient Solar Cells with Boron-Doped Passivated Contacts Energies passivating contacts poly-Si layers laser activation thermal stability electrical deactivation reactivation |
| title | Three-Step Process for Efficient Solar Cells with Boron-Doped Passivated Contacts |
| title_full | Three-Step Process for Efficient Solar Cells with Boron-Doped Passivated Contacts |
| title_fullStr | Three-Step Process for Efficient Solar Cells with Boron-Doped Passivated Contacts |
| title_full_unstemmed | Three-Step Process for Efficient Solar Cells with Boron-Doped Passivated Contacts |
| title_short | Three-Step Process for Efficient Solar Cells with Boron-Doped Passivated Contacts |
| title_sort | three step process for efficient solar cells with boron doped passivated contacts |
| topic | passivating contacts poly-Si layers laser activation thermal stability electrical deactivation reactivation |
| url | https://www.mdpi.com/1996-1073/17/6/1319 |
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