Industrial-Scale Preparation of Nanocrystalline n-Type Silicon Oxide Front Contacts Using N2O as an Oxygen Source for High-Efficiency Silicon Heterojunction Solar Cells

Abstract

The advantage of employing an n-type hydrogenated nanocrystalline silicon oxide (nc-SiO_x:H) layer as the front surface field (FSF) in silicon heterojunction (SHJ) solar cells is due to its low optical absorption coefficient and tunable refractive index. However, carbon dioxide (CO₂) gas, one of the major precursor gases in the nc-SiO_x:H layer, deteriorates the crystallinity, which is one of the key factors affecting cell performance. Here, we successfully deposited a nc-SiO_x:H FSF layer with high crystallinity for SHJ solar cells by using nitrous oxide (N₂O) as an alternative oxygen source instead of existing CO₂. Compared with the use of CO₂, the use of N₂O as an oxygen source can achieve a 10% ~ 15% increase in the deposition rate of the nc-SiO_x:H layer, which can shorten the total processing tact-time, thus having the potential to reduce production costs in large-scale industrial applications. The influence of N₂O as an oxygen source on the film properties was also investigated. By optimizing the proportion of N₂O in the precursor gases, we finally fabricated 274.5 cm²-area SHJ solar cells with an in-house average efficiency of 25.76%, which is approximately 0.1%_abs higher than that of their reference counterparts (using CO₂ as an oxygen source), and obtained a certified efficiency of 25.79% for the champion cell independently confirmed by the ISFH CalTeC in Germany.