Thermal Stability of Nitrogen-Doped Tunnel Oxide Passivating Contact Structures for Future Chalcogenide/Silicon Tandem Solar Cells

Abstract Chalcogenide/silicon monolithic tandem solar cells (SCs) are regarded as promising candidates for next-generation photovoltaic technology. Tunnel oxide passivating contact (TOPCon) technology, with its inherent resilience to high thermal budgets, is well-suited for the bottom cell in such tandems. To further mitigate parasitic light absorption and carrier nonradiative recombination losses in TOPCon when integrated into tandem devices, a wide-bandgap, nitrogen (N)-doped TOPCon structure is adopted in this work. We investigate its thermal stability after a high-temperature preparation process followed by post-annealing (300–600 °C, 10–30 min) on standalone TOPCon samples. The results indicate that Si–Hn bonds in the N-doped TOPCon structure are more prone to breakage during high-temperature processing than those in N-free counterparts, revealing fragile thermal stability. During post-annealing, substantial hydrogen released from the SiNx:H dielectric layer recombines with Si dangling bonds, significantly improving passivation performance. However, excess hydrogen accumulates at the localized Ag–Si contact interface, deactivating dopants and increasing contact resistivity on both sides after post-annealing of SCs, regardless of whether the TOPCon structure contains the N-dopant or not. A subsequent LECO (laser-enhanced contact optimization) treatment effectively reactivates the dopants and largely restores the electrical properties. These findings provide a foundation for optimizing N-doped TOPCon bottom SCs toward future integration into two-terminal monolithic chalcogenide/silicon tandem devices.