Growth and Characterization of the Evaporated Quaternary Absorber Cu2FeSnS4 for Solar Cell Applications
Cu2FeSnS4 (CFTS) was synthesized by direct fusion of high-purity elemental copper, iron, tin and sulfur. CFTS thin films were deposited on glass substrates heated by single source vacuum thermal evaporation, after which the obtained samples were annealed under a sulfur atmosphere in a sealed quartz tube at 400°C for 1 h in order to optimize the CFTS stannite phase. The substrate temperature was varied from room temperature to 200°C. The formation of a stannite structure with (112), (200) and (004) planes in the powder and thin films was confirmed using x-ray diffraction measurements and the crystallites were found to have a preferred orientation along the (112) direction. Optical measurements analysis showed that after the sulfurization process the layers have a relatively high absorption coefficient close to 105 cm−1 in the visible spectrum. The films show a direct optical band gap in the range 1.30–1.63 eV for substrate temperature varied from room temperature to 200°C. All samples revealed p-type conductivity as determined by the hot probe method.