Formation Energies of Point Defects in Copper Indium Diselenide Using ab initio Methods
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Formation energies of point defects in copper indium diselenide using ab initio methods C. Domain1, J.M. Raulot1,S. Laribi1, S. Taunier 2 and J.F. Guillemoles3 1 EDF-R&D, Département MMC, Les Renardières, 77250 Moret sur Loing, France 2 EDF-R&D, CISEL project, Quai Walter, 78401 Chatou Cedex, France 3 ENSCP, LECA, UMR 7575, 11 rue Pierre et Marie Curie, 75005 Paris, France
ABSTRACT The opto-electronic properties of CuInSe2 and related compounds depend on their defect chemistry in a way that is far from being understood and in which ab initio calculations could help by providing new insights as shown previously. Ab initio calculations of energy and electronic structure of various intrinsic (including defect pairs) and extrinsic (including potential dopants such as Zn) point defects have been performed in the chalcopyrite semiconductors CuInSe2, some of them being computed for the first time by advanced ab initio techniques. The method used is based on the density functional theory within the framework of pseudo-potentials and plane waves basis set. The results are discussed in view of the existing data, models and calculations. INTRODUCTION Cu(In,Ga)Se2 showed promises in the field of solar energy conversion since some 25 years. It is today the compound giving the highest efficiencies of all thin film technologies both for small cells [1] and for modules [2]. Yet undoubtedly, one of the factors that impeded a fast technological development is the complexity of the material and the risk associated with that complexity. In particular, several aspects related to electronic properties and defect chemistry are not fully understood: dopability and especially in relation with stability and nature of the dominant defects (bulk and surface), and their relationships with sample composition. These aspects could benefit from ab initio approaches [3, 4, 5]. CuInSe2 can be taken as a model material of the Chalcopyrite family of compounds and it is expected that the results of the present calculations also shed some light on the other members of that family. More specifically, we address here issues related to: - Electronic structure analysis based on the Crystal Orbital Hamilton Population (COHP), and its relation to the stability of the material, - Intrinsic and extrinsic (Zn) defects formation energies, - Association of point defects: structure and formation energies.
COMPUTATIONAL PROCEDURE Ab initio calculation based on the Density Functional Theory using pseudopotentials and plane waves have been performed with the supercell approach. The code used is VASP (Vienna Ab initio Software Package) [6]. The ultra soft Vanderbilt type pseudopotentials (USPP) from the VASP library were used. The electronic configurations of the different atomic species are Cu (3d10 4s1), In (4d10 2 5s 5p1) with the 4d electrons included as semi core electrons and Se (4s2 4p4). The plane wave basis set is truncated with an energy cutoff of 240 eV.
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