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 development future of solar modules depends on a device structure that can complement the electron-selective tunnel oxide passivating contact with an equivalent hole-selective contact.  

The authors* of 'Hole-selective SiN_x and AlO_x tunnel nanolayers for improved polysilicon passivating contacts', published in ACS Applied Energy Materials, investigated plasma enhanced chemical vapour deposited (PECVS) SiN_x and atomic layer deposited AlO_x as alternative nanolayers for the passivation layer in polysilicon tunnel contacts.  They fabricated p⁺ ply-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 (iV_oc) of 698 mV and dark saturation current density (J₀) of 34 fA/cm² for a p⁺ poly-Si contact using a PECVD SiN_x 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.

*Led by this department and collaborating with the School of Engineering at the Ecole Polytechnique Federale de Lausanne (Switzerland).