Large-area n-type TOPCon Cells with Screen-printed Contact on Selective Boron Emitter Formed by Wet Chemical Etch-back

This paper presents large-area TOPCon (tunnel oxide passivated contact) cells with a selective boron emitter formed by a screen-printed resist masking and wet-chemical etchback process. The wet chemical solution with NaNO
₂
catalyst is developed to uniformly etch-back an APCVD deposited and thermally diffused boron emitter from ~47 to ~95 Ω/□ by growing a ~250 nm porous Si layer within 3 min and subsequently removing it. After etch-back followed by a thermal oxidation, J
_θe
was reduced from 85 to 21 fA/cm
²
and sheet resistance increased to 65 and 120 Ω/□ in the p++ and p+ regions, respectively. A solar cell with screen-printed Al/Ag contact on the etched-back selective emitter (65/120 Ω/□) on the front and TOPCon on the back achieved a Voc of 681.9 mV and efficiency of 21.13% on large-area n-type Cz Si wafer, demonstrating the potential of this technology for high-efficiency industrial solar cells.