Improvement in Effective Optical Absorbency for the Bottom Cells of Mechanical Stacked Multi-Junction Solar Cells

Reduction of optical reflection loss at intermediate region of mechanical stacked samples is discussed in the case of top GaP and bottom Si substrates bonded with epoxy adhesive. Transparent and conductive Indium gallium zinc oxide (IGZO) layers with thicknesses of 102 nm were formed on the bottom surface of GaP and the top surface of Si substrates. The insertion of IGZO layers reduced the optical reflectivity of the stacked sample. It successfully gave high effective optical absorbency for bottom substrates, Aeff of 0.93 for wavelength regions for light in which top GaP substrate was transparent and bottom Si substrate was opaque. High Aeff values were maintained by changing the light incident angle from 0 to 50.