Impact of bulk impurity contamination on the performance of high-efficiency n-type silicon solar cells

The experimental variation of wafer thickness and resistivity at device level combined with a comprehensive device simulation study allows the identification of dominating recombination-induced power loss mechanisms in high-efficiency n-type silicon solar cells (A. Richter et al, Sol. Energy Mater. Sol. Cells 173, p. 96, 2017). Under the assumption of specific Shockley-Read-Hall (SRH) recombination parameters, impurity recombination within the silicon bulk was identified as one main source for efficiency losses particularly for solar cells made of high-resistivity silicon. In this work, we extend that analysis approach focusing on the SRH recombination parameters in order to investigate whether certain properties of these recombination-active impurities can be identified using this kind of simulation-based analysis. Reported SRH recombination parameters of various common impurities (eg, Fe, Cr, or Ni) were considered. It was found that a dominating role of certain impurities as Cu, Au, Co, or Zn can be excluded. A general simulation study as a function of the fundamental SRH recombination parameters allowed us to reduce the possible SRH parameters significantly in particular of the capture cross-section ratio of electrons and holes. These results demonstrate that our analysis approach, which combines an experimental variation of wafer thickness and resistivity with a comprehensive device simulation, can provide deep insights into the solar cells loss mechanisms. In particular, the conclusions regarding SRH recombination are of importance for solar cells made of n-type silicon as there are no meta-stable impurity states formed that would allow a direct identification of impurity recombination-related power loss as reported for p-type Si.