Phosphorous diffusion gettering of n-type CZ silicon wafers for improving the performances of silicon heterojunction solar cells

Phosphorous diffusion gettering (PDG) for different kinds of commercial n-type CZ silicon wafers was investigated for the application in silicon heterojunction (SHJ) solar cells. It was found that surplus phosphorus diffusion was effective in improving the effective minority carrier lifetime (τeff). Highest τeff was obtained at the optimal diffusion temperature of 840 °C, which was almost independent on the diffusion duration at a wide region from 5 to 60 min, corresponding to a sheet resistance region from 85 to 21 Ω/sq. The segregation coefficient and gettering sites were considered responsible for the gettering mechanism. When the optimized PDG process was applied to SHJ solar cells with three different groups of commercial Si wafers, the average efficiencies were improved from 21.2% to 22.4%, 21.5% to 22.4%, and 22.1% to 22.5%, respectively, where the efficiency gains were mainly contributed by the improvements of open-circuit voltage and fill factor.