Role of soaking time on the phase evolution of Cu2ZnSnS4 polycrystals synthesized using melting route for photovoltaic applications.

Cu 2 ZnSnS 4 (CZTS) is an emerging quaternary semiconductor material to use as absorber layer for solar cells due its suitable band gap, high absorption coefficient, earth abundancy and less toxic nature. This work provides a comprehensive insight into the phase evolution of CZTS synthesized at a relatively lower process time. In this study, CZTS bulk polycrystals were synthesized using elemental pre cursors via melting route. The influence of soaking time on the structural, compositional and optical properties were investigated using XRD, EDS, Raman, DRS, PL and XPS measurements. XRD pattern revealed a highly crystalline tetragonal structure corresponding to kesterite phase. EDS mapping were performed over a large area of the sample revealed homogeneous distribution and near stoichiometric composition for the sample soaked for 14 h (S14). Raman spectra confirmed the existence of single phase CZTS without any secondary and ternary phases for S14. Diffuse reflectance spectroscopy gave a band gap value in the range 1.34–1.39 eV. PL analysis revealed that asymmetric band shape and higher energy shift is the characteristics of radiative transitions which are influenced by fluctuating potentials. XPS studies confirmed the oxidation states as Cu(I), Zn(II), Sn(IV) and S(II). Image 1 • Melting route is used to synthesize CZTS polycrystals. • Effect of soaking time on phase purity of CZTS is discussed in detail. • Crystallite size increased from 41.40 to 50.56 nm, which increased proportionally with increase in soak time. • Composition of 14 h soaked CZTS sample approached near to stoichiometry. • Temperature rate profile of 1 °C / minute and soaking of 14 h resulted in obtaining phase pure CZTS. [ABSTRACT FROM AUTHOR]