Internal chemical potential in mixed covalent-ionic photosensitive systems

The internal chemical potential Γ of mixed covalent-ionic systems represents the potential differences between the covalent and the ionic intrinsic defect states located within the ionic gap. It is the key parameter to control the carrier densities, the stability regimes, and the photosensitive properties of materials. In this work, we describe first the quantitative analysis of the carrier densities in dependence on the internal potential Nπ(Γ) based on the common features of the electronic structure of mixed covalent-ionic materials. Subsequently, this method is applied on two mixed covalent-ionic materials, i.e., formamidinium lead triiodide and gallium oxide, as representatives of the respective families of perovskites (halides) and transparent conducting oxide thin films. Based on this analysis, the carrier densities as well as the photosensitivity mechanisms and the related specific properties of these materials in dependence on their internal chemical potential are discussed.