Light Scattering Enhancement by Double Scattering Technique for Multijunction Thin-Film Silicon Solar Cells

Abstract

Light trapping is an important technique to increase the efficiency of thin-film silicon solar cells. Textured surfaces are known to scatter sunlight while it passes through thin-film solar cells, thereby increasing the optical pathlength and, thus, the photon absorption in the devices. In this paper, microtextured glass superstrates were prepared by the aluminum-induced texturization (AIT) method. These superstrates achieve high transmission haze values of up to 60% while maintaining a high total optical transmission. We demonstrate that both the surface structure and the roughness of the textured glass surface can be controllably adjusted by changing the AIT process parameters. Approximately 900-nm-thick aluminum-doped zinc oxide (AZO) films are deposited onto the microtextured glass surfaces by magnetron sputtering and then further textured using wet-chemical etching in diluted HCl, creating an AZO surface that features both micrometer-scale and submicron-scale structures. Optical spectroscopy and goniophotometer measurements reveal that the light scattering capability of the substrates increases significantly due to the wet-chemical AZO texturization. The combination of microtextured AIT glass, together with the submicron-textured AZO, could be very attractive for high-efficiency double-junction micromorph thin-film Si solar cells, whereby the amorphous Si top cell benefits significantly from the AZO's submicron texture and the microcrystalline Si bottom cell benefits primarily from the microtextured glass surface.