Electronic conduction mechanism and optical spectroscopy of Indigo carmine as novel organic semiconductors

Indigo carmine (IC) is an organic material dye that can be used as an organic semiconductor. The IC powder pellet was characterized by X-ray diffraction (XRD), Fourier transforms infrared spectroscopy, AC\DC electric conductivity and optical diffused reflectance spectroscopy. The XRD measurements revealed that the IC powder is crystallized in triclinic system structure with the space group P₁ and both the optimized lattice and refinement cell parameters have calculated before and after refinement for the first time by using the program Crysfire and Checkcell software. The Kubelka–Munk model was used to determine the band gap energies of the IC powder pellet. Based on this model, the IC powder pellet presents two band gaps equal to 1.982 and 1.689 eV in the studied photon energy ranges. The first optical band gap (1.982 eV) is related to the basic HOMO–LUMO transition, and the other optical transition gap (1.689) is related to the trap inside the HOMO–LUMO gap i.e. onset/inset gap. The multi-band gap of IC powder can enhance the light absorption and can make this material suitable for organic solar cell devices. The dielectric parameters are analyzed and investigated. The DC electrical conductivity upon reciprocal (1000/T) of IC powder was determined by using the two-probe electrical conductivity measuring instrument. The AC electrical conductivity and dielectric properties can support the charge-hopping carriers of barriers of various heights. IC is a promising organic semiconductor material for various aspects in the field of organic technology.