Impact of cell textures on angular cell-to-module ratios

Abstract

Two emerging trends in multicrystalline silicon cell texturing are plasma texturing, and metal catalyzed chemical etching. Both processes roughen silicon surfaces in order to increase light absorption. These processes are attractive as they are applicable to diamond-wire sawn wafers. This work investigates the optical properties of these surfaces, and other conventionally textured surfaces like isotropic acidic and random pyramid textures, are investigated for cells in air and after encapsulation for a large range of angles of incidence. We find that the angular optical performance in air varies strongly with cell texture, but when embedded in a module structure these variations are significantly mitigated: the advantages of a high angular absorption of solar cells are not fully transferred to the module level. This is especially notable for plasma etched, black silicon cell structures which suffer comparatively from poorer index matching and light recycling inside a module structure. The losses caused explicitly by the module embedding (described in the cell to module ratio) are in the range of 1–5% for perpendicular incoming light, and increase to 6–15% at an angle of incidence of 70°. Based on these angular performances, we calculate the annual yield of the modules and find that it varies by less than 2% for the cell textures. Nevertheless, the annual optical yield for the black silicon cell structures are the highest, whereas the metal catalyzed chemical etching cell structures show the lowest performance. Further, we find that different annual distributions of the incoming light at the two investigated locations (Melbourne and Alice Springs) only impact the relative performance of the cell textures at high module tilt angles.