Enhanced passivation and stability of negative charge injected SiNx with higher nitrogen content on the boron diffused surface of n-type Si solar cells

This paper explores the potential of the negatively charged SiNx using plasma charge injection technology to passivate the front textured boron-diffused emitter of n-type Si solar cells. The high-x value single SiNx layer with x ≥ 1.30 (x = N/Si) previously developed for the planarized rear-side passivation of p-type silicon solar cells, with an excellent passivation and charge stability, was found to be unacceptable for the passivation on the front textured boron emitter of n-type cells due to a severe bulk lifetime degradation issue. Therefore, in this study, we investigated a new concept of depositing a dual-x SiNx with a low-x SiNx layer (x∼1.01) on top of a high-x SiNx layer (x∼1.30) for passivation of the front textured rough surface of boron diffused emitter in n-type cells. The optimized dual-x SiNx stack reveals the promise of charge retention for more than 25 years in field operation as well as excellent passivation of boron-doped emitter without bulk lifetime degradation. N-type cells with the optimized dual-x SiNx after charge injection show comparable cell performance to Al2O3 passivated reference cells. The results of cell-level light stability tests using one-cell minimodules exhibit cell performance decay characteristics similar to the traditional Al2O3/SiNx passivated reference module. •The charge retention ability of plasma-induced negatively charged single-x SiNx, as well as dual-x SiNx films was investigated for the passivation of boron emitters in an attempt to replace the Al2O3 passivation.•Significant improvement in the passivation quality of the dual-x SiNx passivated p+ emitter without bulk lifetime degradation after negative charge injection, which makes it comparable to the cell performance of a traditional Al2O3 passivated boron emitter.•Mini-modules fabricated using n-type cells with B emitter passivated with negatively charged SiNx stack showed excellent charge retention ability under simulated sunlight, resulting in passivation quality and reliability comparable to Al2O3 passivated boron emitter reference cells.