Effective Surface Recombination of p⁺ Layers Doped Using Ion Implantation or Surface Deposited B Sources

Two key factors need to be fulfilled in order to enable high efficiency bifacial p-type PERT cell. High bulk lifetime values retention during production processes, and minimized effective surface recombination, S_eff in the p⁺ layer. The influence of boron doped layer parameters on the effective surface recombination in the p⁺ layer of an n⁺-p-p⁺ bifacial PERT solar cell is evaluated. Back IQE data of n⁺-p-p⁺ cells with over-doped p⁺ layer were used for evaluation of S_eff values in the p⁺ layer. Simulation was made for several doping profiles with the surface doping concentration, B_s, in the range 10¹⁸ - 10²⁰ cm^-3. According to simulation, the dominating parameter controlling the effect of the built-in charge in the passivation layer on the effective surface recombination is the B_s level. For B_s values above ∼10¹⁹ cm^-3 this charge has no significant influence. p⁺ layer doping was made by B ion implantation as well as by thermal diffusion from deposited B source. Measurements were performed on symmetrically B doped n-Si wafers with different passivation. Good agreement between simulation and measurements was found.