Passivating Polysilicon Recombination Junctions for Crystalline Silicon Solar Cells

Polysilicon recombination junctions whose n-type bottom layers double as a passivating contact to the silicon surface are investigated. Such recombination junctions are a key element in the interconnection of tandem devices with a silicon bottom cell, and they could be used to simplify the processing sequence of single-junction cells with interdigitated back contacts (IBCs). Polysilicon tunneling junctions require high processing temperatures to crystallize the layers; however, this also facilitates interdiffusion of dopants, whereas tunnelling relies on degenerate doping concentrations in the constituent layers and sharp interfaces between them. Using secondary-ion mass spectrometry (SIMS) in dynamic mode, it is found that dopants diffuse readily across the interface, thus compromising the junction. The undesired diffusion is suppressed by modifying the interface with C, O, or a combination of these. Moreover, it is found that the modification does not interfere with diffusion of H, an essential element to passivate defects at the surface of the silicon wafer. Thus, implied open-circuit voltages (iV(oc)) of up to 740 mV are demonstrated for contact resistivities less than 40 m omega cm(2).

Automated summary

The study investigates polysilicon recombination junctions in which the n-type bottom layer also functions as a passivating contact to the silicon surface. It is found that modifying the interface with C, O, or a combination of these can suppress undesired dopant diffusion without interfering with the diffusion of H, an essential element for passivating defects on the silicon wafer's surface. This modification allows for implied open-circuit voltages (iV(oc)) of up to 740 mV with contact resistivities less than 40 m omega cm(2).