Hybrid-Functional Calculations on the Incorporation of Na and K Impurities into the CuInSe2 and CuIn5Se8 Solar-Cell Materials

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• 作者：Elaheh Ghorbani ; Janos Kiss ; Hossein Mirhosseini ; Guido Roma ; Markus Schmidt ; Johannes Windeln ; Thomas D. K眉hne ; Claudia Felser
• 刊名：Journal of Physical Chemistry C
• 出版年：2015
• 出版时间：November 12, 2015
• 年：2015
• 卷：119
• 期：45
• 页码：25197-25203
• 全文大小：467K
• ISSN：1932-7455

文摘

We have studied the energetics, atomic, and electronic structure of Na and K point defects, as well as the (Na鈥揘a), (K鈥揔), and (Na鈥揔) dumbbells in CuInSe₂ and CuIn₅Se₈ solar cell materials by hybrid functional calculations. We found that although Na and K behaves somewhat similar; there is a qualitative difference between the inclusion of Na and K impurities. Namely, Na will be mostly incorporated into CuInSe₂ and CuIn₅Se₈ either as an interstitial defect coordinated by cations, or two Na impurities will form (Na鈥揘a) dumbbells in the Cu sublattice. In contrast to Na, K impurities are less likely to form interstitial defects. Instead, it is more preferable to accommodate K either as K_Cu substitutional defect, or to form (K鈥揔) dumbbells on Cu substitution positions. Our data show that all (Na鈥揘a), (Na鈥揔), and (K鈥揔) dumbbells can form in both CuInSe₂ and CuIn₅Se₈. In the Cu-poor CuIn₅Se₈ material the pristine Cu vacancies act as the most stable sites where Na and K can be inserted. The formation energy of Na-related defects is generally lower than the corresponding K-related defects, which would mean that if a defect site is already occupied by Na, then it is less likely that K is able to substitute Na during the postdeposition treatment. Regarding the electronic structure of the materials, Na and K point defects located in the Cu sublattice do not create deep defect levels in the gap, so they are not detrimental for the solar cell. In contrast, Se-related substitutional defects introduce defect levels in the gap, which act as charge traps, leading to severe degradation of the device efficiency. However, the formation energy of these Se-related defects are high so that they should have a low concentration in the material.