Stoichiometry‐Driven Interdependencies in PECVD a‐SiN x :H Films: Linking Hydrogen Behavior, Optical Properties, and c‐Si Solar Cell Performance

Amorphous hydrogenated silicon nitride (a‐SiN x :H) is an industry‐standard dielectric for crystalline silicon solar cells. However, its stoichiometry‐driven behavior continues to limit solar cell performance and manufacturing reliability. In this study, the interplay among film composition, hydrogen dynamics, and interface quality is systematically investigated by varying the SiH 4 ‐to‐NH 3 gas flow ratio ( R *) during plasma‐enhanced chemical vapor deposition. A critical stoichiometric regime ( R * = 0.09) is identified that maximizes the fixed charge density and defect passivation while minimizing process‐induced shunting. Si‐rich films exhibit reduced density and accelerated hydrogen release, which lead to Ag‐induced emitter shunting, whereas N‐rich films exhibit insufficient hydrogen passivation. Optical modeling and external quantum efficiency analysis further demonstrate that refractive index and parasitic absorption are tightly coupled to film stoichiometry and contribute to short‐wavelength current losses. A process–structure–function framework that links nanoscale bonding configurations to macroscopic solar cell reliability is established, which offers design rules for robust dielectric interfaces. These findings directly apply to emerging high‐efficiency structures—including perovskite/silicon tandems and back‐contact solar cells—where dielectric reliability and hydrogen management are decisive for scalable deployment.