High-Efficiency Multicrystalline Silicon Solar Cells: Potential of n-Type Doping

In this study, we demonstrate the potential of multicrystalline (mc) n-type silicon for the fabrication of highly efficient mc-Si solar cells. High-quality mc n-type silicon wafers are obtained from a research ingot crystallized in a high-purity crucible, using high-purity granular silicon as seed layer in the crucible bottom and high-purity polysilicon feedstock for the block. An mc p-type silicon block crystallized under identical conditions (same seed and feedstock, crucible system, and temperature profiles) serves as reference and enables measurements of the interstitial iron and chromium concentrations by metastable defect imaging. In combination with 2-D simulations for in-diffusion and precipitation of chromium, the limitation of n-type high-performance mc silicon by these metals is assessed after different solar cell processing steps. Material-related efficiency losses are assessed by an "efficiency limiting bulk recombination analysis,"which combines injection-dependent photoluminescence imaging of minority charge carrier diffusion length with PC1D cell simulations. Finally, based on this material, boron-diffused front-junction mc n-type silicon solar cells with a full-area passivated rear contact (TOPCon) are fabricated. The record cell features an efficiency of 19.6%, which is the highest efficiency reported for an mc n-type silicon solar cell.