2D-modelling of Metal-Si Emitter Interface Assuming Schottky or Ohmic Contact

Abstract In this study we investigate, using a two dimensional simulation tool, the characteristics of the metal-Si emitter interface of screen printed and firing through contacts. In the model we assumed that the metal contact to n+ or p+ emitters is either Ohmic or Schottky and the dominant current conduction mechanism flow is directly through Ag-crystallite. The simulation results were then compared with the experimental data for the contact resistance (ρc) and fill factor (FF) of p-type cells with an n+ phosphorous diffused emitter and n-type cells with a p+ boron diffused emitter. The emitters of p-type and n-type cells were metalized using an Ag paste or, in case of p+ doped emitters, by an AgAl paste. From the modeling of Si-emitters contacted by a screen printed Ag paste, a Schottky contact, assuming literature value for Ag work function, agrees with the experimental IV data for n+ emitters, but does not agree for the p+ emitters. Assuming only a Schottky contact at metal-p+ emitter interface, the model fails to estimate simultaneously VOC and FF of the cells contacted by an Ag paste. Thus, the current transport mechanism at Ag- p+ emitter interface may not be dominated by direct metal-Si contact through Ag-crystallites imprints but, possibly, by tunneling through a thin interface glass layer that resulted (in this case) in high contact resistance as observed experimentally. Therefore modeling Ag-p+ emitter interface using an Ohmic contact with a high contact resistance agrees better with the experimental IV data.