Indium chalcogenides

The indium chalcogenides include all compounds of indium with the chalcogen elements, oxygen, sulfur, selenium and tellurium. (Polonium is excluded as little is known about its compounds with indium). The best characterised compounds are the In(III) and In(II) chalcogenides e.g. the sulfides In₂S₃ and InS.
This group of compounds has attracted a lot of research attention because they include semiconductors, photovoltaics and phase-change materials. In many applications indium chalcogenides are used as the basis of ternary and quaternary compounds such as indium tin oxide, ITO and copper indium gallium selenide, CIGS.

Some compounds that were reported and have found their way into text books have not been substantiated by later researchers. The list of compounds below shows compounds that have been reported, and those compounds that have not had their structure determined, or whose existence has not been confirmed by the latest structural investigations, are in italics.

There are a lot of compounds, the reason for this being that indium can be present as

The compound In₂Te₅ is a polytelluride containing the Te₃²⁻ unit.
None of the indium chalcogenides can be described simply as ionic in nature, they all involve a degree of covalent bonding. However, in spite of this it is useful to formulate the compounds in ionic terms to get an insight into how the structures are built up. Compounds almost invariably have multiple polymorphs, that is they can crystallise in slightly different forms depending on either the method of production, or the substrate upon which they are deposited. Many of the compounds are made up of layers, and it is the different ways that the layers are stacked that is a cause of polymorphism.

In₆S₇ is an n-type semiconductor.

...
Wikipedia