Boron Selective Emitter Formation With Un-metallized J0e of 13fA/cm2 For Silicon Solar Cell Applications

This paper describes the development of a novel selective boron emitter formed a screen-printed negative resist to form vias for heavily doping regions. Ion-implantation and atmospheric pressure chemical vapor deposition (APCVD) are used to from the field (p+) and heavily doped regions (p++) of the emitters, respectively. This approach gives better control over the surface concentrations/junction depth for each region of the emitter resulting in very low full area emitter dark saturation current density (J0e) of 6fA/cm
²
for the lightly doped regions and ~93fA/cm
²
for the heavily doped regions. Very low un-metallized J0e of 13fA/cm
²
and 18fA/cm
²
were achieved for selective emitters with 30 Ω/\square p
⁺⁺
region in combination with 200 and 150 Ω/\square ion-implanted p+ regions respectively. A metallized J0e of 28fA/cm
²
was achieved with 3% screen-printed metal grid contact coverage to p
⁺⁺
regions of the selective emitter. This selective emitter gave 0.4% absolute increase in efficiency over standard NPERT with a 150 Ω/\square homogeneous emitter.