Figure 4. Optical experiments of the ultra-thin wafers.

(a) Measured reflectance of the 50 μm Si wafers with the standard light trapping structures (75 nm SiN_x ARC and Al back reflector) and the rear Ag NP light trapping, with the inset image showing the self-assembly Ag NPs (scale bar: 1 μm) (b) Absorption enhancement spectrum of the ultra-thin wafers from 50 μm to 2 μm, with the inset image showing the electrical profile at 800 nm for the 2 μm Si wafer with optimized square array of rear located Ag NPs (c) Reflectance of the two reflectors: standard reflector and the plasmonic reflector, with glass slide as superstrate for measurement (d) Experimental integrated absorption of the rear plasmonic solar cells and the standard cells, excluding the particle induced losses, in comparison with the FDTD modelling.