(a) The system under consideration. P is the grating period, FF is the grating fill factor, and d is the thickness of the Si layer. The horizontal diameter of the grating feature is P × FF. The front part is coated with an ITO layer of 50 nm thickness. (b) The proposed computational method which replaces the rough diffuser structure with a computational boundary and reduces the simulation domain to a single period of the grating.
Computational scheme assuming a lossless back diffuser or reflector. (a) One pass field profile calculations. (b) OPC iteration.
Reflectance versus wavelength for flat top structures in the case of 30°incidence angle for different back reflectors. The inset shows the structure.
(a) The spatial power density spectrum of the wavefront coming out of the diffuser. (b) The corresponding radiant intensity profiles. α is the angle relative to the normal of the diffuser surface. The “narrow diffuser” radiant intensity has a Lorentzian shape with a linewidth of π/6 rad.
Reflectance calculated with the OPC method of flat top (dotted curves) and grating top (solid curves) structure, for various types of diffusers.
Escape transmittance ( ) of relaunched plane waves for (a) flat top structure (d = 2.5 μm) and (b) grating top (P = 400 nm, d = 2.5 μm). In all cases, the ITO thickness is 50 nm.
Reflectance curves for the fully coherent and one pass coherent cases for top grating-flat bottom solar cell structures with different Si thicknesses. The top grating structure is the same as shown in Fig. 1(a) with P = 400 nm.
Plot of versus Si thickness d for the structure of Fig. 7 .
Comparing the fully coherent and OPC case for (a) P = 400 nm with d = 2.5 μm and d = 7.5 μm, and for (b)P = 1000 nm with d = 2.5 μm and d = 7.5 μm. For all structures, the bottom reflector is 100% specular, FF= 0.7 and grating depth of 300 nm. The dotted line plots are the reflectance for the fully coherent case. The solid line plots are the average reflectance of the fully coherent case, with wavelength averaging window 20 nm. The circle plots are the reflectance for the OPC case.
Total reflectance of combined diffuser-grating structure (P = 400 nm, d = 2.5 μm) assuming different specular components for the diffuser. For comparison, the reflectance of an all flat structure without any front grating and back diffuser under OPC condition is the black dashed line. The geometrical parameters of the top grating are P = 400 nm, FF = 0.7, grating depth of 300 nm, and ITO thickness of 50 nm.
Total reflectance of combined diffuser-grating structures and single element structures. The geometrical parameters of the top gratings are the same as in Fig. 10 .
(a) WIR versus Si thickness. (b) WIR versus % of specular reflection at different Si thicknesses for the combined structure.
Total and first-pass reflectance of combined structures with front gratings and Lambertian back diffuser for several different grating periods. The gratings have fill factor 0.7 and grating depth 300 nm. The Si thickness is d = 7.5 μm and the ITO thickness is 50 nm.
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