Annealing and Firing Stability of in situ Boron-doped poly-Si Passivating Contacts

This paper focusses onto the first successful realization of an industry-relevant in situ B-doped direct-plasma PECVD process for p-type TOPCon as well as the fundamental understanding of the junction’s working principle. A key element in this approach is controlling the diffusion of B across the poly-Si/SiOx/c-Si junction upon high-temperature annealing. More precisely, the influence of different thermally grown interfacial oxides, an intrinsic a-Si(i) layer below the highly doped a-Si(p) film as well as an additional native SiOx interlayer in between those a-Si layers are investigated. Both high passivation qualities (J0s<7 fA/cm2) and low contact resistivities (ρc<5 mΩcm²) are obtained on planar surface. When implementing those layers at the rear of both-sides contacted p-type front emitter TOPCon solar cells, a very high Voc of 719.5 mV and η up to 22.8% were achieved. Furthermore, it is found that p-type TOPCon reveals an enhanced thermal stability upon firing up to 850°C with a single SiNx layer compared to n-type TOPCon and does not require an additional AlOx layer.