Narrow Results

In₂S₃ thin films with different S/In molar ratios (from 1.5 to 3.5) were deposited via a spray pyrolysis technique on glass substrates at 340^∘C. Then, the obtained films were annealed at the same temperature 400^∘C for 2h. X-ray diffraction study reveals the formation of cubic $\beta$-In₂S₃ phase with (400) as preferred orientation. The crystallite size varies in the range 64–97nm. Optical analysis exhibits that transmittance in visible and near infrared regions is higher than 65% for all films. The optical band gap varied from 2.58eV to 2.67eV. The optical parameters (refractive index, extinction coefficient, dielectric constants) were calculated through the transmittance ($T$) and reflectance ($R$). Dispersion parameters ($E_0$, $E_d$), high frequency dielectric constant (${\epsilon }_{\infty }$), refractive index ($n_{\infty }$), oscillator length strength ($S_0$), average oscillator wavelength (${\lambda }_0$) and optical moments ($M_{-1},M_{-3}$) were determined by Wemple–DiDomenico model. The surface and volume energy losses with photon energy were also calculated. The optical and electrical conductivities were estimated. These properties of In₂S₃ films are important for photovoltaic applications.

$\beta$-In₂S₃ thin films ($\mathrm{\text{S/In}}=1$, 2 and 4) were prepared using the pneumatic spray pyrolysis (PSP) route to analyze the effect of the S/In ratio on the physical properties. These properties were conducted using the photothermal deflection spectroscopy (PDS) method. The PDS signal amplitudes as a function of wavelength show multiple reflections which appear for all prepared In₂S₃ films. Such multiple reflections indicate homogeneity and high crystalline quality of the films. The deduced values of the optical band gap vary in the range 2.55–2.65eV. The highest thermal diffusivity is obtained for $\mathrm{\text{S/In}}=2$. The product ($\mu \cdot \tau$) is found in order of 10${}^{-8}$cm${}^{-1}$/V. The estimated carrier diffusion lengths are 0.06, 0.11 and 0.09$\mu$m for films corresponding to $\mathrm{\text{S/In}}=1$, 2 and 4, respectively. Defect absorption in $\beta$-In₂S₃ films is also investigated by PDS. Five absorption peaks are observed. These absorption peaks contain defect information in the band gap. Hence, this work evidences that $\beta$-In₂S₃ is a multi-functional material that can be used in optoelectronic, photovoltaic and visible-irradiation photocatalyst applications.