Development of Cost-Effective Codiffusion Process for TOPCon-IBC (TBC) Solar Cell Precursor Fabrication

This work presents a novel codiffusion process to simplify the fabrication of tunnel oxide passivated contact (TOPCon) based interdigitated back contact (IBC) solar cell precursor. This process enables the formation of three regions, emitter (p-TOPCon), BSF (n-TOPCon), and n⁺ FSF (lightly phosphorus-doped) in a single high-temperature step, which significantly reduces the thermal budget and process complexity compared to traditional IBC solar cell fabrication, enhancing its industrial viability. The iVoc of 721 mV was achieved with TOPCon-IBC solar cell precursor fabricated in this work using the codiffusion process. Excellent surface recombination current density (J0s) as low as 4.3 fA/cm² for the p-TOPCon layer and 1.1 fA/cm² for n-TOPCon layer were achieved, along with low contact resistivities (ρc) of 3.5 and 0.8 mΩ-cm², respectively. These parameters were incorporated into 3-D device simulations, which identified the optimal combinations of emitter and BSF region widths for maximizing cell efficiency. The simulation projected that successful integration of all investigated technologies in this study could enable TBC solar cells to reach an efficiency of 25.4%.