Atomic-scale Structure of Complex Semiconductors for Thin Film Solar Cells (Prof. Claudia Schnohr)

Atomic-scale Structure of Complex Semiconductors for Thin Film Solar Cells
Prof. Claudia Schnohr (Leipzig University)
Thursday March 30, 2023
Photovoltaics, particularly thin film solar cells, are anticipated to significantly contribute to the sustainable energy supply of the future. In this regard, complex semiconductors such as Cu(In,Ga)Se2 or Cu2Zn(Sn,Ge)Se4 are being increasingly utilized and investigated as absorber materials in thin film solar cells due to their capacity for specific tailoring of material properties by adjusting alloy composition. Nonetheless, this complexity also results in intrinsic structural inhomogeneity at the subnanometer scale, as two different types of atoms are situated on a specific site of the crystal structure. Consequently, the local atomic arrangements in these semiconductor alloys often differ from the average crystal structure, and this deviation significantly affects critical material properties, including the band gap energy.
To address this issue, we employed Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy to identify element-specific bond lengths of complex semiconductors such as Cu(In,Ga)Se2 or Cu2Zn(Sn,Ge)Se4. Based on these outcomes, we modelled the atomic displacements of the various local configurations and assessed their impact on the band gap energy using ab initio theoretical calculations. Our findings contribute to a comprehensive understanding of the intricate relationship between composition, structure, and properties of semiconductor alloys and enable the realization of their complete technological potential.