Jensen I J T, Gorantla S, Løvvik O M, Gan J, Nguyen P D, Monakhov E, Svensson B G, Gunnæs A E, Diplas S
SINTEF Materials and Chemistry, P/O box 124 Blindern, 0314 Oslo, Norway.
J Phys Condens Matter. 2017 Nov 1;29(43):435002. doi: 10.1088/1361-648X/aa8799.
The interface between ZnO and CuO has been predicted to be a good candidate for use in thin film solar cells. However, the high predicted conversion efficiency has yet to be fully realized experimentally. To explore the underlying causes of this we investigate the interface between ZnO and CuO in magnetron sputtered samples. Two different sample geometries were made: In the first set thin layers of ZnO were deposited on CuO (type A), while in the second set the order was reversed (type B). Using x-ray photoelectron spectroscopy (XPS), an intermediate CuO layer was identified regardless of the order in which the CuO and ZnO layers were deposited. The presence of a CuO layer was supported by transmission electron microscopy (TEM) results. Changes in the electron hole screening conditions were observed in CuO near the interface with ZnO, manifested as changes in the relative peak-to-satellite ratio and the degree of asymmetric broadness in the Cu 2p peak. The suppression of the Cu 2p satellite characteristic of CuO may cause the CuO presence to be overlooked and cause errors in determinations of valence band offsets (VBOs). For the type A samples, we compare four different approaches to XPS-based determination of VBO and find that the most reliable results are obtained when the thin CuO layer and the altered screening conditions at the interface were taken into account. The VBOs were found to range between 2.5 eV and 2.8 eV. For the B type samples a reduction of the Cu 2p-LMM Auger parameter was found as compared to bulk CuO, indicative of quantum confinement in the CuO overlayer.
氧化锌（ZnO）与氧化铜（CuO）之间的界面被认为是薄膜太阳能电池的理想候选材料。然而，其预测的高转换效率尚未在实验中完全实现。为了探究其潜在原因，我们研究了磁控溅射样品中ZnO与CuO之间的界面。制备了两种不同的样品几何结构：第一组是在CuO上沉积ZnO薄层（A型），而第二组顺序相反（B型）。使用X射线光电子能谱（XPS），无论CuO和ZnO层的沉积顺序如何，都识别出了一个中间CuO层。透射电子显微镜（TEM）结果也证实了CuO层的存在。在与ZnO界面附近的CuO中观察到电子空穴屏蔽条件的变化，表现为相对峰-卫星比和Cu 2p峰不对称展宽程度的变化。CuO特有的Cu 2p卫星峰的抑制可能导致CuO的存在被忽视，并在价带偏移（VBO）的测定中产生误差。对于A型样品，我们比较了基于XPS测定VBO的四种不同方法，发现当考虑到薄CuO层和界面处改变的屏蔽条件时，可获得最可靠的结果。发现VBO在2.5 eV至2.8 eV之间。对于B型样品，与块状CuO相比，发现Cu 2p-LMM俄歇参数降低，这表明CuO覆盖层中存在量子限制。
