Laser-fired contact silicon solar cells on p- and n-substrates

A fabrication process is described that is simple, uses conventional equipment and yet is capable of producing highefficiency crystalline silicon solar cells. It is based on a deep phosphorus diffusion to form the front emitter region and a deep aluminum diffusion to form a back BSF region. The total charge of phosphorus atoms is controlled to the desired level in a conventional open-tube POCl, furnace by adjusting the mix of gases that flow into it, the time and the temperature. A thin SiO, layer is grown in the same diffusion tube to passivate the surface. After aluminum deposition on the back side, the wafers go directly to a second furnace where both dopants are drove in for a relatively long time and at a high temperature. One of the nicest things of this process is that it minimizes wet etching and cleaning steps. The resulting devices have a relatively thick, moderately-doped and surface-passivated emitter well suited for low cost metallization techniques.