Influence of Fe-B pairs on minority carrier lifetime, trapping density and internal quantum efficiency in mono-crystal Si solar cells

Solar-grade p-type Czochralski silicon wafers are doped with phosphorus by single-face and double-face diffusions, and the influence of Fe-B pairs on the minority carrier lifetime, the trapping centers density and the internal quantum efficiency IQE of cells fabricated from the wafers is analyzed by measuring microwave-detected photo-conductance decay minority carrier lifetime. In the doped wafers with single-face diffusion, the minority carrier lifetime is determined mainly by the density distribution of Fe-B pairs. However, in the doped wafers with double-face diffusion, the minority carrier lifetime is less influenced by the concentration distribution of Fe-B pairs than by other impurities and defects. Numerical calculation based on the combination of the transient voltage signal and the trapping model indicates that the density of trapping centers is reduced by either of diffusion process. On the other hand, detailed analysis of selected specific spots in one wafer with single-face diffusion shows that Fe-B pairs are not the major factor influencing the density of trapping centers. The wafers with different diffusion processes are fabricated into c-Si solar cells and the IQE is measured by using a light beam induced current. The results show that the IQEs of cells with double-face diffusion are higher than those with single-face diffusion, which demonstrates the negative effect of Fe-B pairs on the IQE of solar cells.