Designing of Seebeck coefficient and electrical conductivity in CZTS thin films for giant power factor

Abstract

In this work, we develop a new technique to simultaneously increase the Seebeck coefficient and electrical conductivity in order to achieve a giant power factor. 16 samples of CZTS thin films (TFs) are synthesized using the chemical solution method by varying the Cu+2, Zn+2, Sn+2 and S+4 mol concentrations alternatively. This variation of molar concentration generates secondary phases in the grown TFs which cause an enhancement in the value of Seebeck coefficient and mobility of carriers. The calculated absolute values of electrical conductivity and Seebeck coefficient and power factor are found to be 884 μV/oC, 183 S/cm and 1.43 × 10−2 Wm−1K−2 respectively for sample having a molar concentration of Cu atoms 2.5 mM. We carefully optimized these values with the number of extra secondary (binary and ternary) phases and it is found that sample grown using the molar concentration of Cu 2.5 mM has the highest density of secondary phases. This behavior of thermoelectric properties with a number of secondary phases is also tested for all 16 samples and a similar trend is observed. To support the existence of secondary phases, we have performed a number of characterization techniques such as x-ray diffraction, Raman spectroscopy, scanning electron microscope (SEM) and UV/Vis spectroscopy. All data presented in this manuscript suggested that power factor can be enhanced significantly by controlling the number of secondary phases. © 2019 Elsevier Ltd and Techna Group S.r.l.

Keywords CZTS TFs, Power factor, Raman spectroscopy, Secondary phases, X-ray diffraction