Chemical stability of CuInS 2 in oxygen at 298 K
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Chemical stability of CuInS2 in oxygen at 298 K J. Grzanna and H. Migge Hahn-Meitner-Institut Berlin GmbH, Glienicker Straße 100, D-14109 Berlin, Germany (Received 12 June 1995; accepted 28 October 1996)
A thermochemical analysis is performed in the quaternary system Cu–In–S–O at 298 K, including the respective four ternaries. The Cu–In phase diagram is updated with respect to the new experimental as well as to the new thermochemical results in the literature. Free energies of In6 S7 , In2.8 S4 , CuIn2 , and Cu2 In2 O5 have been estimated. Consistent sets of data are used for the calculations of the ternary systems with the program THERMO, and the results are used to calculate the quaternary tetrahedron Cu–In –S–O with the program THERMOQ; the algorithm is given. Twelve quaternary two-phase equilibria have been found. They are used to calculate predominance area diagrams of the quaternary system with the program STADIAQ for different oxygen partial pressures. The algorithm of this program is given. From these diagrams it becomes obvious that CuInS2 is unstable in air and even in UHV systems and should react to form In2 (SO4 )3 and Cu2 S at oxygen pressures larger than log ps pascald 251.5. The results are useful for research in fields such as oxidation and crystal growth of CuInS2 and for development of processes for producing this compound.
I. INTRODUCTION
CuInS2 is of interest as a possible photovoltaic base material, and has been produced by such methods as CVT,1 evaporation,2,3 and solution growth from indium and copper-indium solutions.4–6 Recently a CuInS2 based solar cell with 10.2% efficiency has been developed by thermal coevaporation.7 For a better understanding of these methods, the overall phase relations were investigated in the whole system Cu–In–S at room temperature,8 and for the cuts In–CuInS2 ,9 Cu–CuInS2 ,10 and Cu2 S–In2 S3 .11 Furthermore, thermochemical analysis of the system at 298 K12 and 723 K13 have been performed. Independent from the method of preparation, the samples of CuInS2 are often investigated in air at room temperature. The question is whether the surface of CuInS2 will be chemically attacked by oxygen and what the products of reaction will be. No reliable measurements or calculations are known in the quaternary system Cu–In–S –O. Therefore, a consistent set of free energies of the compounds of the system including some estimations is generated. The ternary equilibria in the Gibbs triangles and the quaternary equilibria in the tetrahedron are calculated by using the programs THERMO13 and THERMOQ. Predominance area diagrams of the ternary and quaternary systems are constructed using the program STADIAQ. The results for different oxygen pressures are shown, and the stability of CuInS2 in air at 298 K is discussed. The algorithm of the programs is given. J. Mater. Res., Vol. 12, No. 2, Feb 1997
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II. STABLE PHASES AT 298 K AND THEIR FREE ENERGIES A. Cu –In–S system A thermochemic
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