Hole-Selective SiN<inf>x</inf> and AlO<inf>x</inf> 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) SiNx and atomic layer deposited AlOx 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 (iVOC) of 698 mV and dark saturation current density (J0) of 34 fA/cm2 for a p+ poly-Si contact using a PECVD SiNx 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.