Postdeposition treatments (PDTs) with sodium fluoride (NaF) and potassium fluoride (KF) were introduced as a way to improve the efficiency of Cu(In,Ga)Se₂ (CIGS) based solar cells. Here, we apply postdeposition treatments with rubidium fluoride (RbF) to low-temperature coevaporated CIGS absorbers after a first PDT with NaF and compare the effects of the addition of Rb and K on the solar cell performance and material properties of the CIGS films. KF and RbF PDTs lead to similar improvements in the open-circuit voltage (V_oc) and fill factor (FF), while allowing a reduction of the thickness of the cadmium sulfide (CdS) buffer layer without loss in electronic performance. KF and RbF PDTs lead to comparable modifications of the morphology and composition of the CIGS films. After the PDT, K and Rb accumulate in a nanopatterned copper-poor secondary phase at the CIGS surface, while also diffusing within the CIGS layer and strongly reducing the concentration of lighter alkali element sodium. These findings corroborate theoretical calculations published by another group, which predicted the segregation of potassium indium selenide (KInSe₂) and rubidium indium selenide (RbInSe₂) at CIGS surfaces under the used PDT conditions.

中文翻译：

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氟化Rub和氟化钾后处理对Cu（In，Ga）Se ₂薄膜和太阳能电池性能的影响

引入氟化钠（NaF）和氟化钾（KF）的后沉积处理（PDTs）作为提高基于Cu（In，Ga）Se ₂（CIGS）的太阳能电池效率的方法。在这里，我们在使用NaF的第一个PDT之后，将氟化rub（RbF）的沉积后处理应用于低温共蒸发CIGS吸收器，并比较了添加Rb和K对CIGS薄膜的太阳能电池性能和材料性能的影响。KF和RbF PDT导致开路电压（V _oc）和填充系数（FF），同时允许减小硫化镉（CdS）缓冲层的厚度而不会降低电子性能。KF和RbF PDT导致CIGS膜的形态和组成具有可比的修改。在PDT之后，K和Rb积累在CIGS表面的纳米级贫铜次级相中，同时也在CIGS层中扩散并大大降低了较轻碱金属钠的浓度。这些发现证实了另一组发表的理论计算，该理论预测了在使用的PDT条件下，硒化钾铟硒（KInSe ₂）和硒化rub铟硒（RbInSe ₂）在CIGS表面的偏析。