Double-layer antireflection coating of MgF₂/SiN_x for crystalline silicon solar cells

Single layer antireflection coatings are not able to cover a broad range of the solar spectrum. This research investigated changes in the performance parameters of crystalline silicon solar cells caused by a thin film of magnesium fluoride (MgF₂) deposited on top of a silicon nitride (SiN _x) film already deposited on the emitter layer of a solar cell. The MgF₂ film depositions on crystalline cells of large area (125 mm × 125 mm) were carried out by using thermal evaporation under high vacuum (∼10^-6 Torr) with a special mask to protect the front metal contact on the busbars after cell fabrication. Significant improvements in the conversion efficiency (Eff) and the short-circuit current (I_SC) of the cells were obtained after deposition of the MgF₂ layer. Comparison of the unsealed quantum efficiencies (QE) before and after MgF ₂ deposition showed a significant improvement in spectral response, especially in the wavelength range above 700 nm. The theoretical reflectance of the surface with a double-layer antireflection (DLAR) coating, as obtained by simulation, was found to be in agreement with the experimentally measured surface reflectance pattern. Single and multicrystalline silicon solar cells with respective conversion efficiencies of 17 and 16 % were fabricated with a conventional solar cell fabrication line.