Tuning the Optoelectronic Properties of ZnO:Al by Addition of Silica for Light Trapping in High-Efficiency Crystalline Si Solar Cells

Highly transparent electrodes with a well-tuned refractive index are essential for a wide range of optoelectronic devices, such as light emitting diodes and solar cells. Here, it is shown that the transparency of ZnO:Al can be improved and its refractive index can be reduced simultaneously by the addition of SiO₂ into the layer. It is found that for low SiO₂ concentrations, Si quenches oxygen vacancies and improves the layer transparency. At higher SiO₂ concentrations a highly transparent amorphous compound of Zn_xSi_yO:Al forms, with a refractive index that scales down with the relative Si/Zn ratio. These layers are tested in Si heterojunction solar cells by inserting them between Si and the metallic rear contact of such devices. A consistent improvement is found in the cell short-circuit current density and external quantum efficiency with increasing Si incorporation. Our findings establish a general strategy to tune the optical properties of transparent conductive oxides for improved light management in solar cells.