Ion-implanted poly-crystalline silicon (poly-Si), in combination with a tunnel oxide layer, is investigated as a carrier-selective passivating contact in c-Si solar cells based on an interdigitated back contact (IBC) architecture. The optimized poly-Si passivating contacts enable low interface recombination, resulting in implied VOC (iVOC) of about 720 mV and 704 mV for n-type and p-type, respectively, before any hydrogenation step. It is found that high-quality passivation can be obtained when confining the dopants within the poly-Si layers and realizing a shallow diffusion of dopants into the c-Si bulk, meaning a sharp decrease in doping concentration in the c-Si at the poly-Si/c-Si interface. The doping profile at the poly-Si/c-Si interface can be influenced by poly-Si layer thickness, poly-Si ion-implantation parameters, and post-implantation annealing conditions. The detailed discussion on the passivation properties of the poly-Si passivating contacts and their preparation conditions are presented in this paper. In addition, IBC solar cells with/without front surface field (FSF) are fabricated, with the optimized poly-Si passivating contacts as back surface field, BSF (n-type poly-Si), and emitter (p-type poly-Si). The best cell shows an efficiency of 21.2% (VOC=692 mV, JSC=39.2 mA/cm2, FF=78.3%, and pFF=83.5%).
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