Microwave Annealing for Fast and Effective Hydrogen Activation in Polycrystalline Silicon Passivating Contacts

Hydrogenation is a crucial step in the fabrication of high-efficiency silicon solar cells. In this study, the effectiveness of hydrogen activation is demonstrated via microwave annealing of hydrogen-rich dielectrics coated on poly-Si passivating contacts. This method is compared with conventional hydrogenation techniques, such as annealing in N₂ in the presence of a hydrogen-rich source (such as hydrogenated aluminum oxide (AlO_x:H), hydrogenated silicon nitride (SiN_y:H), or a AlO_x:H/SiN_y:H stack). Key improvements observed include a reduction in J₀ from 30 to <5 fA cm⁻², an increase in iV_oc from 690 to >730 mV, and an enhancement in effective lifetime (τ_eff) from 0.6 to ≈3.5 milliseconds on phosphorus-doped poly-Si/SiO₂ passivating contact samples. With a very short annealing time of ≈1–2 min, the samples passivated by AlO_x:H, SiN_y:H, or the stack show similar performance to samples subjected to 30 min of nitrogen annealing. Photoluminescence (PL) spectra corroborate the findings regarding the hydrogenation of the poly-Si layer and the c-Si substrate, with an increase in PL intensity after microwave annealing. Ultimately, this work suggests that microwave annealing could be a promising addition, offering flexibility to traditional firing hydrogenation processes.