Optical properties of natural dyes: prospect of application in dye sensitized solar cells (DSSCs) and organic light emitting diodes (OLEDs)

Optical properties (absorbance, fluorescence, and transmittance) of the natural dyes extracted from flower, leaf, bark and rhizome of some plant species available in Nepal have been explored, with the prospect of application in dye-sensitized solar cells (DSSCs) and organic light emitting diode (OLED) employing UV-Vis., Fluorescence and FTIR Spectroscopy. The extraction process was carried out using solvents with a varying polarity index of ca. 0 to 10: cyclohexane (CH), dichloromethane (DCM), acetone, ethanol (EtOH), methanol (MeOH) and double distilled water (DDW). The absorbance was found to depend on the nature of solvent usedthe dye samples, A. vasica Nees (in DDW, acetone, DCM and CH), N. arbor-tristis L (in MeOH and CH), U. dioica L (in EtOH, acetone, DCM and cyclohexane), O. wightiana Wall (in acetone and CH), A. vulgaris L (in DCM and cyclohexane), C. coccinea Wall (in DCM), R. anthopogon D.Don (in DCM) and W. fruticosa L (in CH), showed good absorbance in the visible-region and blue shift in the absorbance maxima was noticed with increase of the polarity index of solvents. Some plant extracts showed intense fluorescence emission in the visible region, which hints at their prospect of application in the OLED devices