Hydrogenation characteristics of p-type poly-Si passivating contacts on textured surface for double-sided TOPCon devices

An effective hydrogenation process for polycrystalline silicon based passivating contacts (TOPCon) is crucial to achieve a very high level of surface passivation. This work examines the hydrogenation characteristics of p-type TOPCon on textured surface morphology by applying dielectric layers such as AlO_x, SiN_x and stacks thereof followed by an activation in a furnace anneal or by fast-firing. In a direct comparison with n-type TOPCon, p-type TOPCon requires higher activation temperatures and a higher activation energy. For a successful integration of n-type and p-type TOPCon into bottom cell precursors with 726 mV implied V_oc for tandem devices, stacks featuring AlO_x are beneficial to increase the thermal stability especially for n-type TOPCon. With regards to fast-firing processes, the influence of an additional pre- or post-annealing step is investigated. The peak firing temperature can significantly be reduced when applying an annealing step beforehand and a post-firing anneal improves surface passivation to recombination current densities J_0s as low as 7.9 fA/cm² for p-type TOPCon on textured surface which is one of the lowest reported in literature.