Application of a boron source diffusion barrier for the fabrication of back contact silicon solar cells

Interdigitated back contact and emitter wrap-through solar cells were fabricated using a diffusion barrier to achieve selective phosphorus diffusion for the patterning of the base and the emitter regions on the cell rear. The addition of boron to the diffusion barrier for emitter formation in the underlying n-type base and for the formation of a back surface field in the case of a p-type base was further examined. Boron was successfully incorporated into the n-type Si for the creation of rear p⁺ emitters in an interdigitated back contact cell. An order of magnitude improvement in the surface recombination velocity to 10³ cm/s could be achieved with a p⁺ surface field applied to the base of p-type wafers. Incorporating this technology, best multi-crystalline emitter wrap-through cell performance could be gained with a 1k-2k Ω/□ surface field; however, the characteristics were rapidly dominated by increased saturation current as the surface field layer concentration was increased.