Silicon interface properties of AlOx and SiNx passivation nanolayers under electric field stress

Surface recombination is a primary cause of efficiency losses in silicon solar cells, which can be mitigated through chemical and field-effect passivation. While both mechanisms depend on the fabrication and temperature treatment processes of thin film dielectrics, recent reports show that an external electric field can drastically change the resulting passivation, primarily focusing on high-quality thermal SiO2. This work presents an industrially relevant passivation stack and analyzes the changes in passivation after annealing under an electric field. A low J0s of 45.3 fA/cm2 was demonstrated on a SiOx/AlOx/SiNx stack using a wet chemically grown SiOx and ∼2.5 nm thick AlOx by annealing under positive surface charge. The improved passivation has been attributed to reduced electron capture velocity at the valence band tail. Detailed interface analysis revealed significant modifications on the interface properties, depending on the polarity of the surface charge, the presence of annealing, and the stack structure. It is proposed that hydrogen migration and hot carrier injection near the interface jointly affect the chemical and field-effect passivation. We highlight this strategy to enhance negative charge density in ultra-thin AlOx through a simple extrinsic method, offering a novel solution to the trade-off between effective passivation and limited conductivity in current tunnel oxide passivated contact solar cell (TOPCon) devices.