The electronic properties study of betanin and their derivatives compound: An explanation to betanin limitation in DSSC application

Computational study on electronic properties of betanin and their derivatives has been explored using time-dependent density functional theory (TD-DFT) methods. The TD-DFT calculation result shows red shift on the absorbance spectrum on the protonated form of betanin, which is beneficial for Dye-Sensitized Solar Cells application due to the lower energy. Structurally, betanin has three carboxyl functional groups. Two of them attached to the pyridine skeleton another one attached to the pyrroline skeleton. The lowest unoccupied molecular orbital (LUMO) of betanin is located near the two carboxylic acid attached to the pyridine skeleton. Through this study we show that the carboxyl functional attached to pyrroline skeleton limits betanin performance in Dye Sensitized Solar Cells. Replacing carboxylic acid at this position with electron donor functional group shows electronic properties improvement. The -OC₆H₅ functional group that is endowed with alkyl chain has a high charge transfer (Q_CT). Moreover the alkyl chain can be beneficial to retain the charge recombination at the TiO₂ surface then finally increase the device performance. This result can be a guide to improve the betanin performance as sensitizer in DSSC application.