Optical properties of pure and doped PVA:PEO based solid polymer blend electrolytes: two methods for band gap study

In this work an innovative experimental method has been proposed to estimate the optical bandgap and determine the types of electronic transitions. Solid polymer blend electrolyte films based on PVA:PEO have been prepared by the well known solution cast technique. It was observed that the absorption increased with increasing aluminum salt concentration and shifted to higher wavelengths. Shifting of absorption edge to lower photon energy indicates a good reactivity between the polymer blends and the aluminum salt which in turn the energy band gap decrement is expected. An increase in refractive index for the doped samples has been observed. The miscibility between the aluminum salt and the polymer blends can be well understood from the linear relationship between the refractive index and the volume fraction of the added salt. The increase of extinction coefficient at high wavelengths was observed. The optical band gap measured from the plots of (αhυ)^x versus photon energy (hυ) was compared to that determined from the optical dielectric loss. From the results of the present work it is understood that in order to avoid the plotting of many figures based on Tauc model, optical dielectric loss must be studied. Further research works are required to satisfy that the optical dielectric loss can be used to estimate the band gap and identify the types of electronic transition. The Urbach energy was found to increase with increasing aluminum salt concentration.