Fraunhofer Institute for Mechanics of Materials IWM
Challenges in materials technology that we tackle with our in-depth understanding of mechanisms, multiscale simulation, and atomistic calculations:
- The combination of transparency and electrical conductivity in the development of transparent conductive oxides (TCOs), which are used in displays, solar cells, and LEDs, for example, requires a balance between sufficient free charge carriers (for conductivity) and as little absorption as possible in the visible range. Conductivity requires free charge carriers (electrons or gaps) that often absorb light, especially in the visible range. Transparency requires a large band gap (>3 eV), but this keeps the number of free charge carriers low.
- To improve the often intrinsically poor conductivity of oxides such as ZnO or SnO₂, additional charge carriers are introduced through targeted doping (e.g., with Al, In, Ga). However, the limited solubility of dopant elements in the host lattice, the formation of secondary phases, and lattice distortions must be taken into account.
- Conductivity depends heavily on the crystal structure (e.g., coordination environment of the ions, overlap of the orbitals). Oxides with s-orbital-based conduction bands (e.g., Sn⁴⁺, In³⁺) offer better conductivity—but not all oxides have this structure and must therefore be evaluated.
- When producing thin films using processes such as sputtering, CVD, ALD, or sol-gel, layer thickness, homogeneity, and defect density must be controlled and adjusted, as they influence crystallinity, defects, density, and thus the optical and electrical properties.