Hole-Selective SiN <sub><i>x</i></sub> and AlO <sub><i>x</i></sub> Tunnel Nanolayers for Improved Polysilicon Passivating Contacts.

A highly efficient hole-selective passivating contact remains the crucial step required to increase the efficiency of polysilicon-based Si solar cells. The future development of solar modules depends on a device structure that can complement the electron-selective tunnel oxide passivating contact with an equivalent hole-selective contact. We investigate plasma enhanced chemical vapor deposited (PECVD) SiN _<i>x</i> and atomic layer deposited AlO _<i>x</i> as alternative nanolayers for the passivation layer in polysilicon tunnel contacts. We have fabricated p⁺ poly-Si contacts with resistivities below 100 mΩ·cm² using these alternative metal oxide and nitride nanolayers. Initial passivation tests yielded low levels of passivation; however, a detailed understanding of the nanolayers elucidated the strategies to improve passivation significantly, achieving an implied open-circuit voltage (<i>iV</i> _OC) of 698 mV and dark saturation current density (<i>J</i> ₀) of 34 fA/cm² for a p⁺ poly-Si contact using a PECVD SiN _<i>x</i> interlayer. These are among the best reported for nitride-based nanolayer tunneling contacts, with research into nitride-based tunneling contacts being still in its infancy.