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Novel Poly-Si:Ga/SiOx Passivating Contacts through Non-Equilibrium Doping
K. Chen, E. Napolitani, M. De Tullio, C.-S. Jiang, S. Theingi, W. Nemeth, M. Page, P. Stradins, S. Agarwal, D.L. Young
c-Si, Contact Resistivity, Poly Si, Passivating Contact, Pulsed Laser Melting
Silicon Materials and Cells
Subtopic: High Temperature Route for Si Cells
Event: 38th European Photovoltaic Solar Energy Conference and Exhibition
Session: 2BO.11.4
144 - 146
ISBN: 3-936338-78-7
Paper DOI: 10.4229/EUPVSEC20212021-2BO.11.4
0,00 EUR
Document(s): paper


Poly-Si/SiOx passivating contacts are one of the key enablers for high-efficiency, low-cost c-Si solar cells. In recent years, record devices have reached efficiencies of 26% in the laboratory and 25% in the industry. The current cell structure utilizing a tunneling oxide passivating contact structure with a back phosphorus-doped poly- Si/SiOx passivating contact and a front boron diffused emitter suffers from large emitter recombination. Thus, replacing the front B diffused emitter with a p-type passivating contact is a route to overcome this deficiency. This gives rise to front/back poly-Si based passivating contacts. To address the low passivation performance of the B-doped poly-Si passivating contacts, we replace B with Ga as a novel p-type dopant to avoid dopant accumulation in the tunneling oxide, which is known to lead to large degradation loss in passivation quality. Here, we introduce a non-equilibrium method via pulsed laser melting to thermally melt and recrystallize the poly-Si and redistribute the dopants, achieving doping concentrations above the solid solubility limit (~4E19 cm-3). We demonstrate a good passivation quality with an iVoc of 721 mV with an active Ga doping concentration in poly-Si >1020 cm-3. Furthermore, we show a low contact resistivity of 33.2 ± 9.3 mΩ∙ cm2 using a diode model calculation. Finally, cross-section scanning spreading resistance microscopy was performed to determine the resistance profile across the non-homogeneously doped poly-Si layer.