Solar cell degradation can occur through many pathways and at the different stages of the fabrication process, notably because of the water condensation. In the case of Cu(In,Ga)Se2 (CIGS) solar cells, the impact of water ingress on Mo back contact can be substantial for not only the film itself but also the device performance and reliability. Microstructural modification, change in film morphology, loss in reflectance, and increased resistivity because of the moisture ingress were observed via X-ray diffraction, transmission electron microscopy, spectroscopic ellipsometry, and four-point probe measurements, respectively. Secondary ion mass spectrometry measurements revealed drastic changes in the alkali (Na, K) profiles in both the CIGS and Mo layers, likely because of the modification of their diffusion coefficient through Mo. This, in turn, negatively impacts the solar cell efficiency by decreasing both fill factor and open-circuit voltage. Additional experiments, modifying the substrate and utilizing a NaF postdeposition treatment, highlight the mechanisms of degradation as being due to both a modification of the Mo/CIGS interface and the lack of alkali diffusion after water ingress.

中文翻译：

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进水对钼薄膜的影响及其对Cu(In,Ga)Se$_{2}$太阳能电池的影响

太阳能电池退化可以通过许多途径和在制造过程的不同阶段发生，特别是由于水冷凝。在 Cu(In,Ga)Se2 (CIGS) 太阳能电池的情况下，进水对 Mo 背接触的影响不仅对薄膜本身而且对器件的性能和可靠性都有很大的影响。通过 X 射线衍射、透射电子显微镜、光谱椭偏仪和四点探针测量分别观察到微结构改性、薄膜形态变化、反射率损失和由于水分进入而导致的电阻率增加。二次离子质谱测量揭示了 CIGS 和 Mo 层中碱 (Na, K) 分布的剧烈变化，这可能是因为它们通过 Mo 的扩散系数发生了变化。反过来，这 通过降低填充因子和开路电压对太阳能电池效率产生负面影响。额外的实验，修改基板并利用 NaF 后沉积处理，强调了由于 Mo/CIGS 界面的修改和进水后缺乏碱扩散造成的降解机制。