Facile designing and assessment of photovoltaic performance of hydrothermally grown kesterite Cu₂ZnSnS₄ thin films: influence of deposition time

Herein, low cost precursor source Cu₂ZnSnS₄ (CZTS) nanocrystalline thin films at various reaction time were successfully synthesized via one step hydrothermal route. Hydrothermal route was employed to achieve control over the size and grain growth of CZTS films. As deposited CZTS films were analyzed for its optoelectronic, structural, morphological and electrochemical properties to investigate the effect of hydrothermal reaction time on growth and photovoltaic performance. The hydrothermal synthesis promoted to high absorption (10⁴ cm⁻¹) of the CZTS film with a decrease in optical band gap energy from 1.52 eV to 1.41 eV. Structural study revealed that, improved crystallinity with A₁ mode of vibration for pure phase kesterite CZTS structure. Morphological transition was observed from nanograins to well grown and compact nanospheres. Compositional analysis illustrates, stoichiometric CZTS film formation with the desired valence state of Cu⁺, Zn²⁺, Sn⁴⁺ and S²⁻ elements. Current density-voltage (J-V) measurement of FTO/CZTS/(0.3 M Eu³⁺/Eu²⁺)/Graphite cell configuration shows, highest photocurrent of 2.60 mA/cm² and open circuit voltage of 754 mV was observed for CZTS₄ sample with best photoconversion efficiency (η) 3.21% under illumination of 30 mW/cm² light intensity. Electron impedance spectroscopy (EIS) showed that, generation of lower charge transfer resistance (Rct) with increase in reaction time.