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.