ANTI-REFLECTION LAYER AT THE TCO/Si INTERFACE FOR HIGH EFFICIENCY THIN-FILM SOLAR CELLS DEPOSITED ON ROUGH LP-CVD FRONT ZnO

ZnO layers with a wide range of surface roughness and morphologies can be deposited by low pressure chemical vapor deposition (LP-CVD). In this paper, we investigate the effect of a low-resistivity TiO2-ZnO bi-layer incorporated as an anti-reflection coating between the rough ZnO front transparent conductive oxide (TCO) and the silicon layer, for thin film p-i-n microcrystalline silicon solar cells. The TiO2 layers are deposited by reactive rfsputtering from a Ti target with a H2O/Ar gas mixture. We study the potential of this coating with respect to TCO surface roughness and morphology and we show that with a TiO2 layer of 55 nm, having a refractive index of ~2.5 at 550 nm we can decrease the reflectance of typical μc-Si:H solar cell at 550 nm down to 6 %, corresponding to reflectance at the glass interfaces only. Depending on the TCO properties, increases in short-circuit current density ranging from 1.7 to of 3.8 % are obtained, the latter value is obtained for a ZnO layer particularly suitable for the growth of microcrystalline silicon solar cells.