Near-optimal composition of CZTS thin film via exploration of copper and thiourea molar concentration in spray pyrolysis technique

Attaining the optimal composition of Cu2ZnSnS4 (CZTS) thin film is a pre-requisite for photovoltaic application. Herein, the near-optimal composition of spray pyrolyzed CZTS thin film has been obtained by varying copper and thiourea molar concentrations in the precursor solution. Different characterization techniques such as x-ray diffraction (XRD), UV-vis spectroscopy, Scanning electron microscopy (SEM) and Energy-dispersive x-ray spectroscopy (EDS) have been employed to determine the changes in absorber layer properties. The CZTS thin films synthesized using Cu-0.016 M exhibits higher crystallinity with the direct band gap of 1.52 eV. Apart from that, the reduction of copper molar concentration in precursor solution minimizes the segregation of surface secondary phase. The variation of thiourea molar concentration facilities the growth of CZTS and reduces the formation of secondary phases. Besides that, the optical studies revealed that the increment in thiourea molar concentration leads to a broadening of band gap from 1.52 eV to 1.61 eV. The CZTS thin films synthesized using copper and thiourea molar concentrations of 0.016 M and 0.12 M showed appropriate absorber layer properties with near-optimal Cu-poor and Zn-rich ratio i.e., Cu/(Zn+Sn) = 0.81 and Zn/Sn = 1.26.