Department Structure and Dynamics of Energy Materials

Point defect analysis of Cu(In,Ga)X₂ chalcopyrite materials

Formation of the vacancy phase CuIn₃Se₅ by the
clustering of defects in Cu-poor CuInSe₂ (B=In, Ga).
Presented at the E-MRS Spring Meeting 2012 and
awarded with the Best-Poster-Prize.

A pre-requisite for a semiconductor with practical application as TFSC absorber material is a tetrahedral coordination, i. e. the cations are tetrahedral coordinated by the anions and vice versa.

This is the case for Cu(In,Ga)X₂ compounds which crystallize in the tetragonal chalcopyrite type crystal structure. Due to the complex production process, the commercial produced Cu(In,Ga)X₂ TFSC exhibit an overall off stoichiometric composition, whereby the crystal structure of Cu(In,Ga)X₂  shows a remarkable tolerance by the presence of high concentrations of native point defects. The type and concentration of point defects shows a remarkable difference for CuInSe₂ and CuGaSe₂. A clustering of point defects to neutral defect complexes of type (2V_Cu + In_Cu) was proved in CuInSe₂ and is assumed to be one reason why CuInSe₂ solar cells achieve considerable efficiencies even when exhibiting large amounts of native point defects ^[1]. When in Cu(In_yGa_1-y)Se₂ the Ga content is increased beyond 0.3, the cell efficiency of these devices decreases. So far the poor performance of Cu(In_yGa_1-y)Se₂ solar cells with 0.3[2].

^{C. Stephan, S. Schorr, H.-W. Schock, M. Tovar: Comprehensive insights into point defect and cluster formation in CuInSe2, Applied Physics Letters 98 (2011) 091906
C. Stephan, T. Scherb, C, Kaufmann, S. Schorr, H.-W. Schock: Cationic point defects in CuGaSe2 from a structural perspective, Applied Physics Letters 101 (2012) 101907}