Enhanced passivation and contact properties of boron emitters through PECVD-deposited double boron silicate glass layers for high-efficiency tunnel oxide passivating contact solar cells

The mainstream industrial-grade boron emitters for n-type tunnel oxide passivating contact (TOPCon) solar cells (SCs) are typically fabricated using low-pressure (LP) boron diffusion technology. Although this approach has achieved great success in the photovoltaic (PV) industry, LP-based boron emitters still face significant challenges in meeting the current demands for high-efficiency c-Si SCs while ensuring safe production. Plasma-enhanced chemical vapor deposition (PECVD)-based boron diffusion technology holds the potential to address these issues, which, however, usually suffers from poor passivation quality, limiting its broader application in the PV industry. In this work, we propose a flexible and controllable method using PECVD to deposit a double-layer boron silicate glass (BSG), combined with high-temperature annealing, for the fabrication of boron emitters. Our results indicate that the PECVD-based boron emitters exhibit a higher surface boron concentration and a shallower boron diffusion depth, which enhance hole transport compared to LP-based boron emitters. Consequently, the PECVD-based boron emitters achieve superior passivation and contact properties, with a high implied open-circuit voltage of 715 mV, a low single-sided saturation current density of 8.8 fA/cm², and a low contact resistivity of less than 0.5 mΩ·cm². Additionally, proof-of-concept TOPCon SCs incorporating such PECVD-based boron emitters are fabricated, achieving a remarkable efficiency of 24.30 %, surpassing that of LP-based TOPCon SCs (23.51 %). This study introduces a flexible PECVD-based boron diffusion technology for TOPCon SCs, demonstrating significantly improved passivation and contact properties and highlighting its potential applications in the PV industry.