Boron-emitter development for TOPCon c-Si solar cells based on plasma-deposited boron diffusion source and poly-Si(n) passivating contact

The n-type TOPCon technology is currently the leading approach in the industry. Generally, it involves two high-temperature steps that can result in long cycle times and expensive processes. In this context, we propose a lean manufacturing process based on the successive PECVD-deposition of the front and rear doped layers, followed by a co-annealing step in which front emitter formation and rear passivating contact activation are performed simultaneously. We first investigated the influence of the PECVD process parameters and the thermal budget of the co-annealing step on the active boron concentration profile, the passivation quality, and contact resistivity. Then, we investigated the effect of a drive-in step under O2 environment to reduce the surface concentration and increase the depth of the emitter. Finally, we investigated the compatibility of the rear passivating contact with the drive-in step. The introduction of the drive-in step made it possible to obtain active boron concentration profiles with the desired surface concentration and depth. However, even though we obtained promising results regarding the compatibility of the rear passivating contact with the drive-in step, we observed that further optimization is necessary to avoid blistering of the n-type poly-Si layer and improve the uniformity of the rear passivation.