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In this paper, Ba-doped SnO2 (SnO2:Ba), Mg-doped SnO2 (SnO2:Mg) and Ce-doped SnO2 (SnO2:Ce) nanostructured thin films were prepared on the glass substrate via a simple and low-cost nebulizer spray pyrolysis method. The crystal structure and morphology of all the samples were investigated by X-ray diffraction (XRD) and field-emission-scanning electron microscopy (FE-SEM), respectively. XRD results suggest that all the samples are polycrystalline with the tetragonal rutile structure. FE-SEM analysis exhibits a uniform surface morphology with homogenous distribution of grains. The transmittance measurement suggests that SnO2:Ba sample exhibits high transparency above 90% in the visible region. We find that doping causes an increase in the band gap, this behavior is explained by the Burstein–Moss effect. Two emission bands in the ultraviolet and visible regions are observed in the photoluminescence spectra. Hall effect measurement reveals that all the samples are degenerate and exhibit n-type semiconducting nature with carrier concentration in the order of 1018 cm−3. Ba doping induces the lowest resistivity of 0.047 Ω·cm associated with an increase in carrier concentration of 8.38 × 1018 cm−3 and mobility of 15.87 cm2 V−1 s−1. In contrast, the incorporation of Mg and Ce in SnO2 reduces the mobility and conductivity, which may be associated with the grain boundary scattering.

The mixed halide CH3NH3PbI3−xClx crystalline thin film has been prepared by two-step solution-processed repeated dip coating method at an ambient atmosphere. X-ray diffraction study reveals the presence of tetragonal and cubic phases in deposited film. Raman study confirms the metal halide bond in the inorganic framework and organic CH3 stretching/bending of C–H bond in CH3NH3PbI3−xClx perovskite. Scanning electron microscopy shows that cuboid and polyhedral-like crystal grains of 100 nm to 2 μm may find applications in optoelectronics. The perovskite CH3NH3PbI3−xClx thin film shows high spectral absorption coefficient of the order of 106 m−1. In optical band gap study, we found the coexistence of cubic and tetragonal perovskite phases. The energy band gap is dominated by cubic phase having Eg = 2.50 eV over tetragonal phase with band gap Eg = 1.67 eV. The room-temperature photoluminescence study confirms band edge, shallow and deep-level emissions. The temperature-dependent cathodoluminescence study shows red, green and ultraviolet emissions. The dominating green luminescence evolved for cubic phase at 2.51 eV. The red and ultraviolet emissions are also found for mixed-phase CH3NH3PbI3−xClx thin film, suitable for preparation of light-emitting devices.

Nano-fiber structure of ZnO and Ni doped ZnO (Ni:ZnO) transparent thin films have been deposited on glass substrate at 350 °C at an ambient atmosphere via spray pyrolysis technique. The structural, surface morphological and opto-electrical properties of ZnO and Ni doped ZnO thin films have been investigated. The XRD patterns show that the films are of polycrystalline in nature having preferential orientation (0 0 2) plane for ZnO changes to (1 0 1) by Ni doping in ZnO matrix. Optical study exhibits red shifting in band gap energy with Ni doping due to sp-d hybridization and display high absorption coefficient of the order of 107 m−1. The photoluminescence (PL) spectra indicate blue emissions in all samples. Electrical measurement confirms the resistivity of the film decreases remarkably with Ni doping and electrical transport is mainly thermally activated. From Hall Effect study, it is confirmed that all the samples are n-type having carrier concentration of the order of 1018 cm−3. Both mobility and carrier concentrations of the films became higher than ZnO sample with the increase of Ni concentration., Materials science; Thin films; Semiconductor; Band gap; Activation energy

Transparent and conducting CdO and Cr doped CdO (CdO:Cr) crystalline films were prepared on glass substrate at 350 °C by cost effective spray pyrolysis technique. Structural analysis indicates CdO:Cr films are polycrystalline cubic structure comprises with spherical or semi-spherical nano-scale particles. The direct band gap energy of CdO was found to change with Cr doping. The photoluminescence (PL) spectra of CdO show extended band edge emissions accompanied by red emission originated from different impurity states. The optical dispersion parameters calculated using Wemple–DiDomenico single-oscillator model were found to vary with Cr concentration in CdO. The dispersion energy of oscillator found to decrease with increasing Cr concentration. Simultaneously, the variation of third-order nonlinear susceptibility with photon energy was found to decrease with increasing Cr concentrations. Hall study confirms that CdO and CdO:Cr films are n-type semiconductor having carrier concentration of the order of ∼1019 cm−3. The obtained physical properties of CdO film were improved by Cr doping which make them suitable for optoelectronic applications.

This work illustrates thickness dependent physical properties of copper indium diselenide CuInSe 2 (CIS) thin films fabricated by a novel two stage electron-beam evaporation technique. Structural analysis exhibits CuInSe 2 phase chalcopyrite structure having preferred orientation in the (112) plane. Absorption coefficient of CIS films have been found very high and associated with band-to-band transition. The optical band gap displays a slight variation from 1.80 eV to 1.90 eV depending on film thickness. Photoluminescence (PL) study reveals the presence of acceptor-type defects in the films. Some other important optical constants, such as refractive index, real and imaginary parts of dielectric constant, optical conductivity and energy loss function are also calculated and found dependent on film thickness. Electrical conductivity measurement confirms CIS films are semiconducting in nature and the activation energy values indicate electrical transport is mainly thermally activated. Hall Effect study confirms CIS films are p-type having carrier concentration of the order of ∼10 26 m -3 .

Nanorod like crystalline CH3NH3PbI3-xClx thin film was prepared by spray pyrolysis at an ambient atmosphere. X-ray diffraction (XRD) and Raman studies reveal the tetragonal perovskite phase of spray deposited film. The optical band gap of CH3NH3PbI3-xClx is estimated to ~1.64 eV which is consistent with vacuum based deposited perovskites. The CH3NH3PbI3-xClx film exhibits a high absorption coefficient of the order of 106 m−1. Photoluminescence (PL) study suggests that band-to-band radiative recombination occurs in CH3NH3PbI3-xClx film. Cathodoluminescence study confirms the emission of 1.67 eV at 80 K and 1.80 eV at 300 K. In this study, the second harmonic generation at photon energy 3.6 eV is reported for the first time at room temperature (RT). It is noted that the band edge peak position at 1.67 eV is being diffused and shifted to 1.80 eV at RT while the second harmonic peak position at 3.6 eV remains unchanged.

Optical and photo-electrical properties of ZnO–CdO films with the ratio of Zn/Cd=1:0, 3:1, 1:1, 1:3 and 0:1 has been studied. XRD study confirms the combination of hexagonal ZnO and cubic CdO phase present in the polycrystalline sample. Atomic force microscopy results indicate that the crystal grains are agglomerated and surface roughness enhanced due to higher Cd concentration in ZnO. From optical studies, it is found that the transmittance and the band gap decreased as Cd content increased. Photoluminescence studies on ZnO–CdO films showed intense near-band edge emissions at room temperature and is attributed to recombination of excitons localized within band tail states likely caused by non-uniform Cd distribution in ZnO–CdO matrix. The dispersion of refractive index was analyzed by the Wemple–DiDomenico single-oscillator model. The third-order nonlinear polarizability is found high with higher concentration of cadmium at higher photon energies. Some other optical parameters such as dissipation factor, optical conductivity, interband transition strength, surface and volume energy loss have been calculated depending on dielectric constant evaluated from optical data. Finally, photoconductive gain and carrier lifetime have been calculated and found dependent on Zn/Cd ratio.

Transparent and highly photoconductive nano-composite ZnO–CdO films were fabricated on glass substrate at 360 °C substrate temperature. X-ray diffraction (XRD) studies indicate that the films are nano-crystalline and contain a combination of hexagonal ZnO and cubic CdO structures. According to scanning electron microscopy (SEM) studies, the surface of the films is found to be rough over large areas favoring photo absorption. From the optical and electrical measurements, it is found that ZnO–CdO composite combines the properties of optical transparency in the visible region with a high electrical conductivity. Based on the characteristics of photoluminescence (PL) and photoconductivity, it seems that Zn/Cd = 3:1 nano-crystalline film is preferable for application as buffer layers in solar cells.