Absorption enhancement in hydrogenated amorphous silicon-based solar cells

Abstract

The enhancement of long wavelength (>600 nm) light absorption by light scattering can result in a significant increase in the short circuit current density of a-Si:H-based solar cells. A model of absorption enhancement is presented and used to predict both light absorption in the active i layer and the total reflectance of single-junction a-Si:H p-i-n solar cells. These results are compared with the corresponding measurements performed on actual solar cells. It is found that the texture imparted to the metallic interface may result in a significant decrease in the reflectance of the rear contact, and in certain of the rear contacts considered, the reflectance is also reduced by interface formation phenomena. These mechanisms reduce the reflectance of the aluminum rear contact to less than 50% in the solar cells studied. In these cells and others where large light absorption occurs in the rear contact, incomplete light randomization is not found to be an important enhancement limiting effect. A thin layer of indium-tin-oxide inserted between the a-Si:H n layer and the contact metal results in critical trapping of scattered light and so reduces light absorption in the rear contact.