Comparison of N and P Type Ribbon Grown Multi-Crystalline Silicon Wafers using Photoluminescence Imaging

Photoluminescence imaging is used to compare similarly grown n-type and p-type string ribbon mc-Si wafers at two stages of solar cell processing. Key advantages of the PL imaging technique are that it is fast, contact-less, requires no sample preparation and is negligibly influenced by trapping artifacts, which can dominate lifetime measurements made by other methods on multicrystalline materials at low and moderate injection levels. We observe that after the light phosphorous diffusion step, the average minority carrier lifetime in the p-type samples is significantly lower than in the n-type samples, with considerable continuity of good and bad grains along the growth direction in both n-type and p-type samples. Striking differences are also found in the effect of SiN passivation on n-type and p-type wafers