Design Of Trilayer Silicon Nitride Thin Films Coating On Physical Metallurgy Polysilicon Solar Cells

In this work, we studied and designed the trilayer silicon nitride thin films coating on physical metallurgy polysilicon solar cells. Initial deposition condition of plasma-enhanced chemical vapor deposition was obtained by PC1D simulation. Optimized condition was then obtained experimentally. Results shown that adding silicon nitride thin films could greatly reduce the surface reflection. Spectroscopic ellipsometer, UV-VL spectrophotometer and life time monitor were utilized to characterize thickness, refractive index and minority carrier lifetime, respectively. The thickness and refractive index of1st,2nd and3rd silicon nitride layer were (27nm,2.682),(13nm,2.457) and (43nm,1.910), with total thickness and effective refractive index of83nm and2.10-2.15, respectively. The reflectivity results shown that the average reflectivity in visible light region was5%, with a0.8%decrease at650nm and greatly improving the incident light adsorption. Electron dispersive spectroscopy (EDS) indicated silicon-rich, with Si:N=2.68:1. In designing, the first layer of silicon nitride served as a good surface passivation layer due to hydrogen enrichment during PECVD process, resulting in an enhancement of minority carrier lifetime from5.93 μs to6.43μs. The short circuit current of fabricated solar cell (156*156cm2) reached8.65A, increased by0.27A comparing with those with bilayer silicon nitride thin film coating. Average photoelectric conversion efficiency was also increased by0.38%and the maximum efficiency reached18.08%. Quantum efficiency (QE) of trilayer silicon nitride thin film coating solar cells was obviously higher than those with bilayer coating. In short-wavelength region, QE increased dramatically, with a peak value of98%; in long-wavelength region, QE decreased slightly.