Characterization of electrical and optical absorption of organic based methyl orange for photovoltaic application

Thin films of methyl orange (MO) were successfully prepared using thermal evaporation technique from their powder. Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) were performed for studying the thermal stability of MO. The surface morphology of thin films was studied by using scanning electron microscopy (SEM). The crystalline structure of MO powder and films were studied by using X-ray diffraction (XRD) and their lattice parameters were found to be the same. The temperature dependence of dark electrical conductivity (σ) and Seebeckʹs coefficient (S) for MO thin films in the temperature range of 300–450 K have been investigated for different thicknesses in the range 300–700 nm. This dependence was found to be typical for p-type semiconductor which was correlated with the MO molecular structure. The optical properties of MO films were investigated by UV–vis spectrophotometry which was analyzed to obtain the electronic transition, optical band gap (Eg) and Urbach energy (E0). An allowed indirect optical transition was observed for MO and the band gap was found to be thickness independent and equal to 2.02 eV. A strong rectification characteristic of Au/MO/n-Si heterojunction was obtained from the current density–voltage measurements under dark condition. The photovoltaic characteristics of the device were studied under 100 mW/cm2 and the effect of film thickness was also considered.