By using the solid-state reaction approach, composite polycrystalline samples of (Bi0.98In0.02)2Te2.7Se0.3/x%Bi2Se3 were created with varying amounts of Bi2Se3, (x = 5%, 10%, 15%, and 20%). The hexagonal crystal structure of the composite was revealed by x-ray diffraction (XRD) with a space group of R$$\overline{3 }$$ 3 ¯ m. The surface of the samples was seen to have secondary particles using a field emission scanning electronic microscope. Every sample displayed the typical semi-conducting behaviour across the entire temperature range. In the complex (Bi0.98In0.02)2Te2.7Se0.3, it was found that bismuth was coordinated with six selenium atoms and there were significant selenium vacancies. With an increase in bismuth selenide concentration, the dissolution pattern shifted to a substitutional pattern. A two fold decrease in electrical resistivity for (Bi0.98In0.02)2Te2.7Se0.3/20%Bi2Se3 composition was seen compared to (Bi0.98In0.02)2Te2.7Se0.3/5%Bi2Se3. The granular material was produced by sintering and scattering of potential barrier, a thermal process that increases the Seebeck coefficient. A 200% increase was observed in thermopower for (Bi0.98In0.02)2Te2.7Se0.3/20%Bi2Se3 compared to (Bi0.98In0.02)2Te2.7Se0.3/5%Bi2Se3 compound. Graphical Abstract