Boron Spin-On Doping for Poly-Si/SiO_x Passivating Contacts

Abstract

Herein, we fabricate and characterize p-type passivating contacts based on industrial intrinsic polycrystalline silicon (poly-Si)/thermal-SiO x /n-type crystalline Si (c-Si) substrates using a spin-on doping technique. The impacts of drive-in temperature, drive-in dwell time, and intrinsic poly-Si thickness on the boron-doped poly-Si passivating contacts are investigated. First, the contact passivation quality improves with an increasing thermal budget (<950 °C) but then decreases again for excessive thermal annealing (>950 °C). Second, the thickness of the intrinsic poly-Si film shows only a little impact on the performance. After a hydrogenation treatment by depositing an AlO x /SiN x stack and subsequent annealing in forming gas, the optimized poly-Si passivating contacts show an implied open-circuit voltage (iV oc ) > 720 mV, together with a contact resistivity (ρ c ) below 5 mΩ cm 2 . These results demonstrate that boron spin-on doping is a promising alternative to the conventional BBr 3 thermal diffusion for the fabrication of p-type poly-Si passivating contacts.

Development of Phosphorus-Doped Nanoscale Poly-Si Passivating Contacts via Inkjet Printing for Application in Silicon Solar Cells

“…From doping profiles reported in the literature ,, and on our SOG-control sample, we aim for a doping concentration within the poly-Si in the range of 1–5 × 10 20 cm –3 , with a rapid drop-off within the c-Si wafer. The high concentration within the poly-Si layer enables the desired band-bending, while a strong in-diffusion into the c-Si wafer may damage the SiO x interlayer and can lead to enhanced Auger recombination. ,, The printed and SOG-control samples studied in the printing process development follow the fabrication steps described in Section 2 and all were annealed at 950 °C.…”

“…Recently, Yang et al have reached a power conversion efficiency of 18.5% by spin-coating the poly-Si layer with commercial P and B-doped solutions on each side of the substrate . Ding et al have also proven the effectiveness of spin-on doping on industrially fabricated samples by reaching i V oc values of 730 and 720 mV for P-doped and B-doped poly-Si passivating contacts, respectively. , …”

“…28 Ding et al have also proven the effectiveness of spin-on doping on industrially fabricated samples by reaching iV oc values of 730 and 720 mV for P-doped and B-doped poly-Si passivating contacts, respectively. 25,29 An alternative way to implement liquid doping is to print the liquid dopant via an inkjet printer. In 2021, Kiaee et al successfully fabricated n-type poly-Si passivating contacts using a PiXDRO LP50 inkjet printer with phosphorus ink, reporting an impressive iV oc of 733 mV.…”

Recent advancements in poly-Si/SiOxpassivating contacts for high-efficiency silicon solar cells: technology review and perspectives

“…The TOPCon cell structure has already shown excellent efficiencies of 24% or higher, and some announcements even claim efficiencies of more than 25% (JinkoSolar has set a new world record with a maximum solar conversion efficiency of 25.7% using its largesize monocrystalline Si TOPCon solar cell), demonstrating that the TOPCon structure will play a crucial role in industrial production. [52][53][54][55][56] The interfacial oxide is an important component because it can efficiently passivate dangling bonds on the c-Si surface, lowering the interface trapped charge density (D it ). The recombination of minority charge carriers at the metal contact is prevented via the presence of a thin interfacial oxide on the poly-Si contact, which acts as a tunneling barrier.…”

“…The TOPCon cell structure has already shown excellent efficiencies of 24% or higher, and some announcements even claim efficiencies of more than 25% (JinkoSolar has set a new world record with a maximum solar conversion efficiency of 25.7% using its large-size monocrystalline Si TOPCon solar cell), demonstrating that the TOPCon structure will play a crucial role in industrial production. 52–56…”