Leveraging Silicon Epitaxy to Fabricate Excellent Front Surface Regions for Thin Interdigitated Back Contact Solar Cells

Epitaxy can be used to fabricate doped front surface regions that enable high interdigitated back contact (IBC) silicon solar cell efficiency. One- and two-dimensional simulations show that an epitaxial layer with a constant phosphorus dopant concentration on the order of 10¹⁷ -10¹⁸ cm^-3 can possess the properties of an excellent front surface region for an n-type IBC cell. With appropriate control of dopant concentration and thickness, the epitaxially grown region passivates a textured surface, and provides the lateral conductivity necessary to enable high fill factor. The combination of these two factors drives a simulated efficiency improvement above 0.3% absolute over an n-type IBC cell with a typical 200-Ω/sq phosphorus diffusion (e.g., from POCl₃). Importantly, the epitaxial front surface region can occupy the entire volume of the pyramidal texture. We, therefore, propose an exemplary process sequence for device fabrication that places texture etching after epitaxial growth.