Engineered optical properties of silver-aluminum alloy nanoparticles embedded in SiON matrix for maximizing light confinement in plasmonic silicon solar cells.

Self-assembled silver-aluminum (Ag-Al) alloy nanoparticles (NPs) embedded in SiO, SiN and SiON dielectric thin film matrices explored as a hybrid plasmonic structure for silicon solar cells to maximize light confinement. The AgAl NPs prepared by ex-vacuo solid-state dewetting, and alloy formation confirmed by X-ray diffraction and photoelectron spectroscopy analysis. Nanoindentation by atomic force microscopy revealed better surface adhesion of alloy NPs on silicon surface than Ag NPs due to the Al presence. The SiON spacer layer/AgAl NPs reduced silicon average reflectance from 22.7% to 9.2% due to surface plasmonic and antireflection effects. The SiON capping layer on NPs reduced silicon reflectance from 9.2% to 3.6% in wavelength region 300-1150 nm with preferential forward light scattering due to uniform Coulombic restoring force on NPs' surface. Minimum reflectance and parasitic absorptance from 35 nm SiON/AgAl NPs/25 nm SiON structure reflected in plasmonic cell's photocurrent enhancement from 26.27 mA/cm (of bare cell) to 34.61 mA/cm due to the better photon management. Quantum efficiency analysis also showed photocurrent enhancement of cell in surface plasmon resonance and off-resonance regions of NPs. We also quantified dielectric thin film antireflection and alloy NPs plasmonic effects separately in cell photocurrent enhancement apart from hybrid plasmonic structure role.