Reduction in optical reflection loss at intermediate adhesive layer for mechanical stacked multi-junction solar cells

We propose a method of reduction in optical reflection loss by transparent conductive Indium Gallium Zinc Oxide (IGZO) for the purpose of fabricating mechanical stacked solar cells. Si and Ge substrates coated with 200 nm thick 0.058 Ωcm IGZO layers were stacked with epoxy-type transparent adhesive dispersed with 20 μm sized Indium Thin Oxide (ITO) particles to form a structure of Si/IGZO/adhesive/IGZO/Ge. Marked low reflectively ranged from 0.33 to 0.38 in wavelength between 1150 and 1600 nm were achieved while conventional stacked sample with the structure of Si/adhesive/Ge had reflectivity ranged from 0.51 to 0.52. Numerical analysis revealed that reduction in optical reflectivity was realized by optical interference matching of IGZO layers and proposed the best thickness of IGZO of 185 nm.