Hydrogen Induced J0 Degradation and Recovery Dynamics in Poly-Si/SiOx Passivating Contacts: Moving Beyond Kinetic Models

Hydrogen is a double-edge sword in crystalline silicon (c-Si) solar cells providing both passivation of bulk and interface defects, improving performance, yet also degrading performance via defect formation in the bulk (LeTID) and at surfaces (SRD). Here we experimentally show that post-fired degradation and the subsequent anneal degradation/recovery cycle of the surface passivation quality, measured by J0 in n-TOPCon structures, corelates with the hydrogen concentration in the tunnel oxide region ([H]SiOx). Fully recovered samples have low J0 values coupled with equilibrium [H]SiOx values, whereas high J0 values corelate with excess [H]SiOx. A trapping-diffusion model captures the dynamics of [H]SiOx during firing, and annealing degradation/recovery cycle, reproducing the observed J0 dynamics. This work satisfactorily reveals the physical origin of the degradation/recovery cycle as simply diffusion of hydrogen between the layers of the Al2O3/n+ poly-Si/SiOx/c-Si passivated contact.