APCVD based stacked co-diffusion for multicrystalline silicon p-PERT solar cells

Abstract

We present a cost-effective approach for bifacial p-type mc-Si PERT (passivated emitter and rear totally diffused) solar cells. One of the key elements is a co-diffusion without the use of POCl3 and BBr3 / BCl3. Both, phosphorous and boron containing silicate glass is deposited on the wafer surfaces at atmospheric pressure by chemical vapor deposition (APCVD). This approach allows diffusions without the need of wafer-spacing. Therefore, the wafers can be in direct contact during the co-diffusion, highly increasing the throughput. This work demonstrates the feasibility of the described approach based on a comparison to a reference process in which the diffusion is carried out with conventional wafer-spacing. Sheet resistance and doping profiles do not depend on the position within a stack of 75 wafers and match with the wafers co-diffused with conventional spacing. Despite the direct contact of the wafers during the stacked codiffusion, no cross-doping was observed. Impurity gettering in stacked co-diffusion is very effective and comparable to the reference process. Finally, a comparison of conventional co-diffused and first stacked co-diffused bifacial p-type mc-Si PERT solar cells is provided.