Investigation on the interface of GZO/ITO double-layered transparent conducting oxide films for solar cells

Abstract

GZO/ITO double-layered films were deposited on non-alkali glass substrates by RF magnetron sputtering with various thicknesses at different deposition temperatures. The total thickness of the double layer was constant (~400 nm), and ITO thin films were prepared at various thicknesses (50, 150 and 250 nm) as function of the GZO film thickness (350, 250, 150 nm) at RT (or 200 ο C). The resistivity of the double layer was found to be dependent on the thickness ratio between the two layers. The resistivity of the double-layered films decreased with increasing ITO film thickness according to the rules of parallel DC circuits of the two single layers. X-ray diffraction showed that the enhancement of the GZO (002) preferred orientation increased with increasing ITO thickness. The crystallinity of the GZO films was strongly affected by the microstructure of the buffer layer, which improved the Hall mobility and decreased the electrical resistivity. On the other hand, the crystallinity of the double layer decreased when the GZO films were deposited on the unstable buffer layer which was under post-annealed circumstances. In the case of the GZO(as-deposited at 200 ο C)/ITO(RT) films, the diffusion of elements occurred between the upper and buffer layers, which caused microstructural changes in the films. This result was observed by scanning electron microscopy and energy dispersive X-ray spectroscopy. The transmittance of the double layer was > 85% in the visible region, which suggests that these films will be suitable for photovoltaic devices.