Choline chloride-based ternary deep band gap systems.

The structural features derived by the UV-VIS spectroscopical analysis of five ternary eutectic systems containing choline chloride as Hydrogen Bond Acceptor (HBA), and ethylene glycol and a second Hydrogen Bond Donor (HBD, water, glycerol, methanol, ethanol, and 2-propanol), have been determined and described in terms of band gap and Urbach energies (BGE and UE). In particular, the relationship between the molar composition of the ternary eutectic systems and the BG and U energies was assessed through the Tauc plot methodology, which revealed a peculiar behaviour of the system containing 2-propanol. Thus, a Design of Experiments (DoE) approach, specifically a two-levels full factorial screening experiment, followed by a Surface Responding Analysis (SRA), allowed to determine the influence of the composition and other operational parameters (temperature and resting time) on the structural disorder of the final ternary eutectic system. An unprecedented effect of the DES-aging was observed on the UE, indicating that the structure of these systems evolves during time by increasing its order. [Display omitted] • The band gap energy can be reduced by adding a second HBD to binary eutectics. • Structural disorder in ternary eutectics decrease with aging. • Urbach energy in ternary eutectics can be determined by UV-VIS Tauc method. [ABSTRACT FROM AUTHOR]