Effects of pH on the optical, structural and supercapacitive properties of BiTe thin films produced via CBD

In this study, BiTe thin films are grown on glass substrates by chemical bath deposition method, at different pH levels. Crystallographic structures, crystal dimensions, dislocation densities and crystallization numbers of thin films are characterized by X-ray diffraction, whereas surface morphologies, roughness and film thicknesses are characterized by scanning electronic microscopy and atomic force microscopy. Surface tensions are calculated by Zisman method using different liquids. Capacitance, energy and power densities are calculated for each pH level by using time-dependent current–voltage measurements. Monocrystalline thin films of Bi2Te3 are observed at pH 3 and Bi4Te5 at pH 11, whereas polycrystalline Bi2Te3 and Bi4Te5 structures are formed at pH 7 and 9, respectively. Surface roughness and film thicknesses of polycrystalline thin films are found to be significantly higher than monocrystalline thin films. Capacitance, energy and power density of BiTe thin films produced at pH 3, 7, 9 and 11 are calculated as 503, 562, 569 and 512 F g−1; 55.19, 61.66, 62.43 and 56.17 Wh kg−1; and 3311.4, 3699.6, 3745.8 and 3370.2 W kg−1, respectively. These results show that capacitance, energy and power density of polycrystalline thin films produced at pH 7 and 9, which have high surface load activity, are higher. Electrical resistivity of Bi2Te3 and Bi4Te5 monocrystalline films are lower than those of the polycrystalline BiTe films.