Effect of substrate temperature on the structural and optical properties of radio frequency sputtered tin sulfide thin films for solar cell application

Tin monosulfide (SnS) thin films were deposited on both soda lime glass (SLG) and Mo-coated SLG substrates by radio-frequency (RF) sputtering at a substrate temperature (Ts) from room temperature (RT) to 420 °C. The structural and optical properties were investigated by performing the scanning electron microscopy, electron dispersive spectroscopy, atomic force microscopy, X-ray diffraction, micro-Raman, and ultraviolet-visible-near infrared spectroscopy measurements. For Ts greater than RT showed the well-defined grain features with increased grain sizes. At 350 °C, the films showed the [S/Sn] ratio close to the stoichiometric SnS. The X-ray diffraction studies unveiled the orthorhombic crystal structure of SnS with the (111) preferred orientation for all the Ts. The Raman analysis confirmed the single phase of SnS without any secondary phases. The optical properties revealed a direct energy bandgap of SnS was around 1.2–1.4 eV and the bandgap decreased with increasing Ts. We fabricated the SnS/CdS heterojunction solar cell with the SnS grown at 350 °C. The device with a structure of SLG/Mo/SnS/CdS/i-ZnO/ITO/Ni/Ag exhibited the power conversion efficiency of 0.35% with an open-circuit voltage of 0.143 V, short-circuit current density of 6.7 mA·cm−2, and fill factor of 40.3%.