Poly-SiOx Passivating Contacts with Plasma-Assisted N2O Oxidation of Silicon (PANO-SiOx)

Abstract

Passivating contacts are crucial for realizing high-performance crystalline silicon solar cells. Herein, contact formation by plasma-enhanced chemical vapor deposition (PECVD) followed by an annealing step is focused on. Poly-SiOx passivating contacts by combining plasma-assisted N2O-based oxidation of silicon (PANO-SiOx) with a thin film of phosphorus (n+) or boron (p+)-doped hydrogenated amorphous silicon oxide (a-SiOx:H) are manufactured. Postannealing is conducted for transitioning a-SiOx:H into poly-SiOx. The aim is to achieve a contact with low absorption and high-quality passivation. It is demonstrated that by tuning the plasma oxidation process time and power, the PANO-SiOx thickness and its passivation quality can be controlled. A higher SiO2 content is observed in PANO-SiOx than in the nitric acid oxidation of silicon (NAOS-SiOx) counterpart. PANO-SiOx acts as a stronger diffusion barrier for both boron and phosphorus atoms compared to NAOS-SiOx, affecting the dopant distribution during annealing. Implied open-circuit voltages up to 751 and 710 mV for n+ and p+ flat symmetric samples, respectively, are demonstrated. With respect to standard thermally grown SiO2 tunneling oxide combined with (in/ex)situ-doped low-pressure chemical vapor deposition poly-Si, this study presents a simple alternative for manufacturing passivating contact fully based on PECVD processes.