Enhancement of light trapping by textured back electrodes in tandem micromorph n-i-p silicon thin film solar cells

Abstract

Highly textured Al-doped zinc oxide and silver double structured (ZnO:Al/Ag) layers were prepared by dc magnetron sputtering on flexible stainless steel substrates for the application to flexible silicon thin film solar cells as a back reflector. The surface texturing of ZnO:Al/Ag back reflectors was performed by the changing in the surface morphology and roughness of Ag films by increasing the deposition temperature from 25 °C to 500 °C. With increasing the deposition temperature of Ag films, the grain size of Ag films increased significantly and the size distribution became irregular, resulting in the increase of surface roughness. The enhanced haze (diffuse reflectance/total reflectance) ratio and the effective light scattering property in the long wavelength region were obtained on the textured back reflector surfaces prepared at high deposition temperature. The absorption characteristics of the single and tandem silicon solar cells were improved remarkably on the highly textured back reflectors compared with the smooth ones. The changes in the surface morphologies of Ag and ZnO:Al/Ag back reflectors depending on the deposition conditions of Ag films and their effects on the light trapping property in the single and tandem junction solar cells were investigated in detail.