Influence of carbon incorporation on PECVD-deposited n+ polycrystalline silicon passivating contacts for high-efficiency solar cells

Understanding and controlling dopant activation and parasitic absorption in polycrystalline silicon (poly-Si) passivating contacts is critical for enhancing the efficiency of tunnel oxide passivating contact (TOPCon) solar cells. In this work, we systematically investigate the effects of carbon incorporation into plasma-enhanced chemical vapour deposited (PECVD) n + poly-Si films, and establish a comprehensive correlation between nanoscale morphology, dopant activation, optical properties, and passivation performance. By tuning methane gas flow during deposition, we demonstrate that carbon incorporation suppresses film crystallization, modulates dopant activation, and alters free carrier absorption via changes in effective mass and local microstructure. Advanced characterization techniques, including spectroscopic ellipsometry, Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), conductive-AFM, and Kelvin probe force microscopy (KPFM), reveal that Si–C bonding and reduced grain size lead to lower work function, and enhanced chemical passivation. Optical simulations confirm a reduction in parasitic absorption by ∼0.1 mA/cm 2 per 100 nm at the rear surface, while lifetime measurements exhibit an implied open-circuit voltage of 747.6 mV and a carrier lifetime of 6.7 ms, among the highest reported values for poly-Si passivating contacts. These findings provide new mechanistic insights into carbon-engineered poly-Si layers and highlight their potential for integration into high-efficiency TOPCon and back-contact silicon solar cells.