Analysis of small area interdigtiated back contact silicon solar cells: The influence of boron diffusion process on cell performances

Twenty five small area (4 cm²) interdigitated back contact silicon solar cells have been fabricated and analyzed within one n-type Czochralski wafer. Although these cells made by an identical process, there is a large distribution of cell efficiencies. The absolute efficiency difference between the best cell and the worst cell is 4.38 %. We found that the distribution of the cell efficiencies is correlated with V_OC and pseudo fill factor (pFF). The photoluminescence lifetime map shows a particular pattern of the boron diffused monitor wafer. This PL lifetime map has strong link to the distribution of the conversion efficiencies of the cells within the wafer. The lifetime map shows that the lifetime is higher of the center wafer than that of the edge wafer. Consequently, compared with the edge cells the cells in the center of the wafer have higher efficiencies. Besides, the bulk lifetime degraded significantly after the high temperature boron diffusion that may cause the higher J₀₁ and lower V_OC. According to this investigation, an optimal process condition for boron diffusion to reach a uniform boron dopant within the wafer and to avoid the bulk lifetime degradation is the critical point for high efficiency full-area IBC cells.