ABSTRACT
The microwave-based plasma treatment facility at the Central University of Punjab Bathinda (CUPB) based on 2.45 GHz has been used to investigate the impact on the electrochemical performance of TiO2. This was accomplished by treating a number of pellets of TiO2 sample material with microwave plasma at an input power of 80 W. The palette is subjected to microwave plasma treatment at 30-, 60-, 80-, and 100-s intervals. Many such characterization methods, including UV-visible spectroscopy, FTIR, XRD, and FESEM, have been applied to the study of the impact of plasma treatment on other physical and chemical properties in the context of untreated pellets. In the 80-s plasma treatment, the FTIR study showed that the (O-Ti-O) vibration band at 500-900 cm-1 was wider than other bands. The UV results showed that an 80-s plasma treatment decreased the sample's band gap by 37% and increased the amount of disordered, amorphous material in the sample that had not been treated. XRD studies show that a sample that was treated with plasma for 80 s has low crystallinity and a high disorder (amorphous) factor. The Nyquist plot showed that the electrochemical charge transfer resistance drops from 7 (not treated) to 4 after 80 s of plasma treatment. In a study of electrochemical performance, a sample that was treated with plasma for 80 s has a capacitance that is 35% higher than a sample that was not treated.
ABSTRACT
The semiconductor Cu2ZnSnSe4 (CZTSe) is a promising candidate for both thermoelectric and photovoltaic energy harvesting applications due to a combination of features such as direct band gap, high absorption coefficient, and low thermal conductivity. We report the solid-state synthesis and characterization of Mn-doped Cu2Zn1-xMnxSnSe4 (x = 0, 0.05, 0.10, and 0.15) in an attempt to explore the effect of isovalent substitution at the Zn site. X-ray diffraction and Raman spectroscopy of all specimens confirmed the formation of a single-phase tetragonal kesterite structure (space group I4Ì ). The band gap obtained by UV-visible diffuse reflectance measurements was 1.42 eV for all compositions. Thermoelectric properties were measured in the range 300-785 K. Electrical resistivity was metallic and reduced on Mn doping, while the Seebeck coefficient exhibited a p-type semiconducting behavior that enhanced on Mn doping, with associated enhancement of the power factor. Lattice thermal conductivity showed a 1/T behavior, falling from about 1.9-2.7 W m-1 K-1 at 300 K to 0.51-0.9 W m-1 K-1 above 750 K. The combined effect of enhanced power factor and reduced lattice thermal conductivity resulted in a figure of merit ZT in the range of 0.19-0.42 above 750 K. Thin-film photovoltaic devices with a CZTSe absorber and an SnSe electron transport layer gave 3.2% efficiency.
