Effect of Al Electrodes on Surface Passivation of TiO_x Selective Heterocontacts for Si Solar Cells

This article presents a comprehensive study regarding the impact of the Al electrode on the surface passivation of three TiO_x-based passivating selective contacts: TiO_x:Al/LiF_x/Al,TiO_x/LiF_x/Al, and a-Si/TiO_x:Al/LiF_x/Al. A deterioration in passivation is recorded after the deposition of the Al electrode at close to room temperature, where the deterioration correlated to the Al thickness. A thin Al (10 nm) electrode resulted in the most severe passivation decline, while samples with a 100 nm Al electrode showed much less passivation deterioration. Furthermore, it is found that a low-temperature annealing step led to a partial recovery of the passivation, particularly in the case of TiO_x:Al/LiF_x/Al and a-Si/TiO_x:Al/LiF_x/Al contacts. The presented discovery in this article provides crucial insight into the importance of characterization and evaluation of passivating contacts, which is demonstrated here to be highly sensitive to the deposited metal thickness and the interfacial layers, as well as to the post-deposition annealing.