Properties of nanostructured pure β-In₂S₃ thin films prepared by sulfurization-assisted electrodeposition

The development of pure-phase semi-conducting buffering materials as the substitution of conventional cadmium sulfide (CdS) is extremely important for the large-scale application of solar cells. Herein, we demonstrated a facile approach to deposit pure-phase indium sulfide (In₂S₃) thin films on the indium tin oxide (ITO) substrates by sulfurizing the co-electrodeposited In₂S₃ films. The effect of sulfurization temperatures (200–550 °C) on the surface morphologies, crystal structures, optical and electrical properties of In₂S₃ films was investigated. The results showed that the highly-oriented pure β-In₂S₃ thin films were obtained as the sulfurization temperature exceeded 250 °C. The obtained β-In₂S₃ films possessed a relatively ideal S/In atomic ratio and a continuous and densely packed surface feature. The optical band gaps of the β-In₂S₃ films have been determined in the range of 1.93 ± 0.01–2.06 ± 0.01 eV, which can be controlled by adjusting the sulfurization temperature. The electrical properties tests demonstrated that the pure β-In₂S₃ films obtained by sulfurizing at 550 °C exhibited the characteristic n-type semiconductors with a low electrical resistivity of 38.8 Ω cm, a carrier concentration of 3.8 × 10¹⁵ cm⁻³ and a carrier mobility of 42.3 cm² V⁻¹ s⁻¹. This facile synthetic route is promising for the preparation of pure-phase In₂S₃ films, and then gives the guidance for future design and synthesis of other metal sulfide films for high-performance solar cells.