Triiodide Organic Salts: Photoelectrochemistry at the Border between Insulators and Semiconductors

Abstract

AbstractThe intriguing properties of triiodide organic salts ([(C6H5)3AsO]2H+I3−, (C6H5CH2)3NH+I3− ⋅C6H5CH3, and [(C6H5CH2)3NO]2H+I3−) have been analyzed in detail using experimental and theoretical techniques. The analysis of crystal structures, density of states distribution and photocurrent generation of this purely ionic materials indicates insulating character of the ground state, whereas semiconducting character in higher excited states is observed. These peculiar properties of the studied compounds are the consequence of a specific electronic structure: very flat dispersion diagrams of the valence and conduction band and highly dispersive character on the higher conduction band. Weak triiodide‐triiodide interactions play the key role in the visible absorption range of these salts, while the charge transfer involving high energy carbon‐centered states is responsible for photocurrent generation. The complexity of the electrochemical reactions and the interactions of the I3− anion with light, solubility in organic solvents and the simplicity of preparation make these materials interesting candidates for application in unconventional optoelectronic devices.