Optical-response assessment of p-type degenerate CuI-based ternaries

Quantify the optical response of p-type degenerate CuI-based ternary compounds to determine whether free-carrier (Drude-like) absorption and optical transitions involving partially empty valence bands extend into the visible range, thereby assessing their actual transparency.

Background

The study identifies 20 CuI-based ternary compounds as p-type degenerate semiconductors with intrinsic holes and finite band gaps. Although their calculated band gaps suggest potential transparency, the presence of partially empty valence bands and substantial formal hole concentrations may introduce additional absorption mechanisms beyond the fundamental band-edge transition.

The authors specifically compare these effects with the second-gap transitions known in n-type transparent conducting oxides. They do not calculate the relevant optical response, leaving unresolved whether Drude-like free-carrier absorption or transitions involving the partially empty valence bands compromise visible-range transparency in the proposed compounds.

References

For the compounds identified here, whose formal hole concentration can reach one hole per formula unit (see Sec.~\ref{sec:rule6}), a quantitative assessment of these contributions requires explicit calculations of the optical response and remains an open question.

— High-throughput computational discovery of CuI-based ternary $p$-type transparent conductors  (2609.31277 - Seifert et al., 25 Sep 2026) in Section “Rule 5: Wide-gap second cation and transparency” (Sec. 4.5)