Papers by Keyword: Optoelectronic Properties

Abstract: This paper presents an in-depth spectroscopic analysis of Al₂O₃-40%TiO₂ coatings deposited via HVOF thermal spraying on a 10CrMo9.10 heat-resistant steel substrate. The study aims to correlate the optoelectronic and structural properties of the coatings with their composition and microstructure. Spectroscopic investigations revealed intense absorption in the visible (VIS) region due to electronic transitions from the valence band to the conduction band of the ceramic materials and high reflectivity in the ultraviolet (UV) region. These properties make the coatings particularly useful for protective systems in solar thermal power plants. The detailed characterization of the optical properties of the Al₂O₃-40%TiO₂ coatings obtained through HVOF technology was made possible by corroborating spectroscopic results. These insights are essential for understanding the mechanisms that govern the performance of these coatings in protective applications under high temperatures and aggressive environments.

Abstract: Tin disulfide (SnS₂) thin films have drawn worldwide attention because of their outstanding performance and earth-abundant constituents. However, problems such as coexistence of complex secondary phases (SnS, Sn₂S₃), the band tailing issue, and bulk defects need to be addressed for further efficiency improvement. In this regard, the present work is intended for the treatment of one of these problems. Herein, a single phase SnS₂ has been obtained using an ultrasonic spray pyrolysis method. which is confirmed by X-ray diffraction (XRD) and energy dispersive X-rays (EDXs) characterization techniques. The substrate temperatures (Ts) were increased from 250 °C to 450 °C, and this significantly improved the film's characteristics, which varied from an amorphous phase and a mixture of crystalline phases, SnS₂ and SnS (for the films obtained at Ts = 250 and 300 °C) to a SnS₂ pure phase with a hexagonal structure (for Ts ≥ 350 °C). The morphological, optical, and electrical properties of SnS₂ films are greatly improved by temperature increases too, especially for the film obtained at 450 °C. This suggests that there are opportunities for further efficiency by using the as-deposited SnS₂ thin film at 450 °C.

Abstract: Transparent conducting oxides (TCO) are semiconducting materials that are electrically conductive as well as optically transparent thus making them suitable for application in photovoltaics, transparent heat transfer windows, electrochromic windows, flexible display, and transparent electronics. One of the methods to enhance the conductivity of metal oxides is doping, however, it can adversely affect the optical transparency of metal oxide. Aluminum (Al) doped zinc (Zn) oxide (AZO) is an important TCO material whose optoelectronic properties heavily rely on the Al doping level. There are various methods to develop AZO thin films. However, since Al and Zn are high vapor pressure materials, and their precise content control isn’t that easy, that’s why we dedicated this study to devise a facile method of Al doping into the ZnO structure. We report a twostep synthesis route to develop AZO thin films over glass substrates. Sub stoichiometric zinc oxide (ZnOx) thin films were sputter deposited over glass employing RF magnetron sputtering at 70W and 9 x 10-3 Torr Ar pressure. To mitigate Zn losses during annealing at 450 °C, the films were first oxidized up to 200 °C in air so as to convert ZnOx into stoichiometric ZnO. To incorporate Al into the ZnO structure, Al was spin coated on top of ZnO from its stabilized sol of 0.07 molar aluminum nitrate nonahydrate in ethanol. The samples were subsequently annealed at 450 °C for 2h in air with a controlled heating ramp of 3 °C/min. The film morphology, microstructure, electronic, and optical characteristics were explored employing scanning electron microscopy, energy dispersive x-ray spectroscopy, Hall effect measurements, and UV-Vis-NIR spectrophotometry, respectively. We found that both the Al and oxygen (O) content affect the optoelectronic behavior of AZO. Even without Al doping, O deficient samples were found to be sufficiently conductive, however, the ZnOx is less transparent relative to O rich stoichiometric ZnO. Furthermore, if ZnOx is annealed at higher temperatures, it causes Zn losses, since Zn is a relatively high vapor pressure material. It degrades the film morphology as well. Once we have ZnO we can confidently treat it at 450 °C to allow Al diffusion into the interiors of the ZnO film. We found that AZO produced via this method is sufficiently conductive as well as transparent.

Abstract: Transparent conducting oxides (TCOs) are wide band gap semiconductors having found their use in optoelectronics, flexible electronics, flat panel displays, electrochromic windows, transparent heater windows, and many more. Aluminum (Al) doped zinc oxide (AZO) is an important TCO material which is being widely investigated for such applications. Its optoelectronic properties can be tuned by adjusting the Al content. In this work we study the variation patterns of the electrical conductivity and the optical transparency of AZO thin films with altering the Al content between 0 and 8 at%. The AZO thin films were prepared by wet chemical synthesis from its stabilized sol of zinc acetate dihydrate and aluminum nitrate nonahydrate dissolved in an ethanol and methanol mix. The morphological, electrical, and optical characteristics of these films were explored employing optical microscopy, Hall effect measurements, and UV-Vis-NIR spectrophotometry, respectively. We found out that annealing induces cracks into the AZO thin films and can severely degrade its electrical conductivity. Therefore, it’s imperative to control the Al content as well as the film morphology and structure. Before studying the effects of the Al content, the cracks were mitigated by optimizing the deposition and annealing conditions. The films were spin coated from its sol at 3000 RPM for 30 seconds. The films were dried at 100 °C and were subsequently annealed at 450°C. Since annealing induced cracks, therefore three coats were applied and annealed each time to mitigate the number of transverse cracks across the thickness of the film. The crack minimization was also confirmed by the enhancement in electrical conductivity. For the uniform crack-free AZO films, the Al doping was found to significantly modify the electronic behavior of the films. We expect an initial increase in the conductivity up to around 2 at% Al doping beyond which a decrease in conductivity is expected due to Al₂O₃ formation.

Abstract: Zinc Oxide (ZnO) thin films were deposited on glass substrate by radio frequency (RF)reactive magnetron sputtering technique at variable Oxygen flow rates while Argon flow rates waskept constant. The effect of oxygen flow rate on structural, electrical, optical properties of nanostructured ZnO thin films were investigated by X-ray diffractometer, scanning eletron microscopy(SEM), Hall effect measurements and UV-Visible spectrophotometer. X-ray diffraction (XRD) datareveals films are polycrystalline hexagonal structure with (002) peak as a preferred orientation andcrystallite size was found to be in range12 nm-16 nm.The electrical resistivity of films decreasesfrom 10^-1 Ω-cm to 10^-2 Ω-cm. All deposited ZnO thin films shows high transmittance above 95% inthe visible range 360 nm-800 nm. The optical band gap and refractive indices have been calculatedusing UV-Vis transmission spectra. Oxygen gas flow rates found to have large impact onoptoelectronic properties of ZnO films.

Abstract: The aim of this work is the production and the characterisation of (SnO₂: (Mn, F)) thin films with appropriate optoelectronic properties required for application as ohmic contacts in photovoltaic application devices. Transparent conducting Manganese-fluorine co-doped tin oxide (SnO₂: (Mn, F)) thin films have been deposited onto preheated glass substrates using the chemical spray pyrolysis (CSP) method. The ([Mn²⁺]/[Sn⁴⁺]) atomic concentration ratio (y) in the spray solution is varied between 0 and 8 at. %. The structural, the opto-electrical and the photoluminescence properties of these thin films have been studied. It is found that the deposited thin films are polycrystalline with a tetragonal crystal structure corresponding to SnO₂ phase having a preferred orientation along the (200) plane. Transmission and reflection spectra reveal the presence of interference fringes indicating the thickness uniformity and the surface homogeneity of the deposited samples. Photoluminescence behaviour of Mn-F co-doped SnO₂ thin films was also studied. Photoluminescence spectra reveal the presence of the defects like oxygen vacancies in the materials. In addition, The electrical resistivity, volume carrier concentration, surface carrier concentration and electrical mobility were determined from Hall Effect measurements and the following results were obtained: n-type conductivity in all the deposited thin films, a low resistivity of 1.50×10^-4 Ω cm, and a high electrical mobility of 45.40 cm² V^-1 s^-1 with Mn co-doping concentration equals to 7 at. %. These experimental results show that the electrical properties of these thin films where greatly improved making them suitable as ohmic contacts in photovoltaic applications devices.

Abstract: In present search, we report theoretical analysis by using DFT (TD-DFT)-B3LYP with 6-31G (d, p) level on the geometries, optoelectronic and absorption characteristics of novel a series of the donor-π-acceptor dyes. Their π-conjugated bridge is based on the thiophene, benzene, pyridine, and pyrazine, the thieno [2,3-b] indole was used as an electron donor (D) and the acid 2-cyanoacrylic was used as an electron acceptor (A) group. The theoretical information of the electronic structures such as energy levels (HOMO and LUMO) and energy gap of the molecules is based on study the dyes in organic solar cells. Consequently the energy levels, energy gap, photovoltaic properties, quantum chemical and absorption parameters of all the dyes have been computed and reported. The calculations show that the dyes under study can theoretically be good photosensitizers in DSSCs. Also, the results show that the LUMO levels of all dyes design lie over the conduction band (Ecb) of the semiconductors TiO₂ (or PC70BM) likewise the HOMO levels lie under the decrease potential vitality of the (electrolytes) comparing to ability of electron transfer from the molecular dye excited state to TiO₂ (or PC70BM) and chargeerenewal after photo-oxidation process, separately.

Abstract: Transparent conducting Cobalt-fluorine co-doped tin oxide (SnO₂: (Co, F)) thin filmswere deposited onto preheated glass substrates using the chemical spray pyrolysis method. The ([Co²⁺]/[Sn⁴⁺]) atomic concentration ratio (y)in the spray solution was varied between 0 and 5 at. %. The structural, electrical, optical and photoluminescence properties of these films were studied. It is found that the thin films are polycrystalline with a tetragonal crystal structure corresponding to SnO₂ phase having a preferred orientation along the (200) plane. Transmission and reflection spectra reveal the presence of interference fringes indicating thickness uniformity and surface homogeneity of the deposited thin films. The electrical resistivity (ρ), volume carrier concentration density (N_v), surface carrier concentration density (N_s) and Hall mobility (μ) of the synthesized thin films were determined from the Hall Effect measurements in the Van der Paw-configuration and the following results were obtained: n-type conductivity in all deposited films, a low resistivity of 1.16×10^-2 Ω.cm, and a high Hall mobility of 15.13×10² cm².V^-1.s^-1with Co concentration equals to 3 at. %. These results show that the electrical properties of these thin films where greatly improved making them suitable as ohmic contact in photovoltaic application devices.

Abstract: In the present work, we report an ab initio investigation of the structural, electronic and linear optical properties of (Na_0.5Bi_0.5)TiO₃ (NBT) in its rhombohedral phase, using a Full Potential Augmented Plane Waves (FP-LAPW) method in the frame work of Density Functional Theory (DFT) with the TB-mBJ potential for a better description of the electronic properties. Firstly a Full structure optimization was performed with a relaxation of atomics positions to minimize the Hellmann-Feynman forces exerted over the atoms. The calculated lattice parameters of the rhombohedral phase of NBT are in very good agreement with experimental values with a deviation of 0.9%. The electronic density of states are presented and commented. The calculated band structure shows that our compound has an indirect band gap of 3.30eV. Furthermore, the optical properties were presented, compared with experimental ones present in the literature and commented.

Abstract: A one-step wet-etching method was developed to prepare the transparent conducting double-layered ZnO:Al films with textured surface for improving the light trapping ability.In this work, we investigated the effects of different deposition and re-deposition conditions including Ar flow rate, working pressure and substrate temperature on the light trapping properties of double-layered ZnO:Al films. Obvious changes for surface morphology of double-layerd films were observed, which displayed the significant influence of the re-deposition process. The double-layered ZnO:Al films presented low resistivity, high optical transmittance and haze value in the visible region, which can meet the requirements of front electrodes.