Comparative study of Cu2XSnS4 (X = Ni, Co, Mn or Fe) films synthesized by spray pyrolysis under air atmosphere, as suitable absorber layers for photovoltaic applications

Abstract

The present work deals with the synthesis of an absorber Cu2XSnS4 sulfide (X = Ni, Fe, Co or Mn) thin films by a spray pyrolysis method on hot substrate and under air atmosphere for low cost solar cell. Chemical composition analyzes by energy-dispersive X-ray spectroscopy (EDS) revealed the presence of all the chemical elements (Cu, Sn, S and Co, Ni, Mn or Fe) with a composition close to the stoichiometry of the layers of Cu2NiSnS4 (CNTS), Cu2CoSnS4 (CCTS) and far from the stoichiometry for the layers of Cu2MnSnS4 (CMTS) and Cu2FeSnS4 (CFTS). The X-ray diffraction (XRD) analyzes showed the crystallization of the desired phase such as the cubic phase of CNTS with a preferential orientation (111) and the stannite phase of CCTS and CMTS with a preferential orientation (112), except for the CFTS film which is poorly crystallized. SEM analyzes show that CNTS, CCTS and CMTS layers exhibit a rather homogeneous and compact surface with nodule distribution. The CFTS layer surface shows excrescences separated by voids leading to a porous and diffusing surface. The optical analyzes indicated a high absorption coefficient of the order of 104 cm−1 in the visible range for all the layers and an optical band gap of 1.62, 1.58 and 1.64 eV for the layers CNTS, CCTS and CMTS respectively, whereas the direct band gap of CFTS film is higher (∼ 2.23 eV). The comparison of CXTS films synthesized in the same conditions demonstrates that the CNTS and CCTS films have the most suitable features (optical, electrical, mechanical and oxidation resistance) to be used as absorbing layer in low cost solar cell.