Degradation of Mg-doped zinc oxide buffer layers in thin film CdTe solar cells
Degradation of Mg-doped zinc oxide buffer layers in thin film CdTe solar cells
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DOI：
10.1016/j.tsf.2019.137556
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发表时间：
2019-12-01
期刊：
影响因子：
2.1
通讯作者：
Sampath, Walajabad S.
中科院分区：
文献类型：
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作者：
Bittau, Francesco;Jagdale, Shridhar;Sampath, Walajabad S.
硫化镉是用于碲化镉薄膜太阳能电池的常规n型缓冲层。众所周知，在高温激活过程中，硫化镉会导致光损耗，硫会扩散到吸收体中。溅射沉积的Mg掺杂ZnO（MZO）由于其透明性和可调的带隙而被证明是碲化镉太阳能电池的有吸引力的缓冲层。它对高温处理也是稳定的，并且避免了在氯化镉活化处理期间元素扩散到碲化镉吸收体中。然而，在并入MZO缓冲层的太阳能电池中观察到退化。的MZO膜表面电位的分析已经揭示了显着的波动，一旦该层暴露于大气中的薄膜的功函数沉积后。这些波动是由于高反应性的水蒸气中所含的MgO的MZO薄膜。这已经使用X射线光电子能谱分析，以确定相应的表面化学变化。氧化锌组分相对稳定，但分析表明MgO在MZO表面上形成Mg（OH）（2）层，其在MZO/CdTe界面处和/或在MZO与氟掺杂的SnO 2之间的界面处形成次级势垒。这会影响填充因子，从而降低转换效率。
Cadmium Sulphide is the conventional n-type buffer layer used in thin film Cadmium Telluride solar cells. It is well known that Cadmium Sulphide causes optical losses and sulphur diffuses into the absorber during high temperature activation. Sputter-deposited Mg-doped ZnO (MZO) has been shown to be an attractive buffer layer for Cadmium Telluride solar cells due to its transparency and tuneable band gap. It is also stable to high temperature processing and avoids diffusion of elements into the cadmium telluride absorber during the cadmium chloride activation treatment. However, degradation is observed in solar cells incorporating MZO buffer layers. Analysis of the MZO film surface potential has revealed significant fluctuations in the thin film work function once the layer is exposed to the atmosphere following deposition. These fluctuations are attributed to the high reactivity to water vapour of the MgO contained in the MZO films. This has been analysed using X-ray Photoelectron Spectroscopy to determine corresponding changes in the surface chemistry. The Zinc Oxide component is relatively stable, but the analysis shows that MgO forms a Mg(OH)(2) layer on the MZO surface which forms a secondary barrier at the MZO/CdTe interface and/or at the interface between MZO and the Fluorine-doped SnO2. This affects the Fill Factor and as a consequence it degrades the conversion efficiency.