Silicon thin-film solar cells with rectangular-shaped grating couplers

As an alternative to randomly textured transparent conductive oxides as front contact for thin-film silicon solar cells the application of transparent grating couplers was studied. The grating couplers were prepared by sputtering of aluminium-doped zinc oxide (ZnO) on glass substrate, a photolithography and a lift-off process and were used as periodically textured substrates. The period size and groove depth of these transparent gratings were tuned independently from each other and varied between 1 and 4 μm and 100–600 nm. The optical properties of rectangular-shaped gratings and the opto-electronic behaviour of amorphous and microcrystalline silicon solar cells with integrated grating couplers as a function of the grating parameters (period size P and groove depth hg) are presented. The optical properties of the gratings are discussed with respect to randomly textured substrates and the achieved solar cell results are compared with the opto-electronic properties of solar cells deposited on untextured (flat) and randomly textured substrates.