Effect of chromium doping on the band gap tuning of titanium dioxide thin films for solar cell applications

A simple and inexpensive spray pyrolysis deposition (SPD) approach was used to produce TiO2 and Cr (2-8) at.%-doped TiO2 thin films. To explore the morphological features of the films, FE-SEM micrographs were used and found that 6 and 8 at.% TiO2:Cr films had fibrous patterns with diameters of 0.45 and 0.78 μm, respectively, while the remainder of the films were agglomerated particles. From X-ray diffraction investigation, it was found that the TiO2 thin films had an anatase crystal phase (tetragonal) up to 6 at.% Cr doping, while an anatase-rutile mixed crystalline phase was identified for 8 at.% Cr doping. The crystallite size of the pristine TiO2 film was 35 nm, while for TiO2:Cr films, it ranges from 35 to 46 nm. The Fizeau fringes technique was employed to measure the thickness of the TiO2 film and 165 nm was found for pristine TiO2 and 164-180 nm for TiO2:Cr films. UV-visible spectroscopy was used to study optical properties such as absorbance, refractive index, optical band gap, dielectric constant, and optical conductivity. As the Cr concentration increases, the optical band gap decreases from 3.40 eV to 2.70 eV. Using the four-point probe method, it was found that the resistivity changes with temperature and is also affected by the Cr content.

Growth, structural, thermal, and optical characteristics of L-asparagine monohydrate doped magnesium sulphate heptahydrate semiorganic crystals

A novel semi-organic crystal has been grown using slow evaporation technique by doping organic compound L-asparagine monohydrate (C4H8N2O3·H2O) with inorganic material Magnesium sulphate heptahydrate (MgSO4·7H2O). The crystallographic parameters like strain, dislocation density and crystallite size were calculated by powder X-ray diffraction method. Functional groups were identified and bond length, force constants were calculated from FT-IR spectroscopy. Energy dispersive X-ray (EDX) analysis was used to identify the constituent elements of the crystal. Kinetic and thermodynamic parameters, such as, activation energy Ea, change in Gibb's free energy (ΔG) and change in enthalpy (ΔH) have been determined by thermogravimetric analysis (TGA) analysis. Ea, ΔH and ΔG show positive values and change in entropy (ΔS) shows negative ones. The thermal degradation behavior of the crystals has been analyzed by differential scanning calorimetry (DSC) analysis. Various optical constants such as optical band gap, lattice dielectric constant, absorbance, extinction coefficient, the ratio of free charge carrier concentration to the effective mass, Urbach energy, optical and electrical conductivities were estimated from UV-vis transmittance data. High optical conductivity (1010 s-1) justifies the good photo response nature of the semi-organic crystal.

Indirect to direct band gap transition through order to disorder transformation of Cs2AgBiBr6 via creating antisite defects for optoelectronic and photovoltaic applications

Non-toxic lead free inorganic metal halide cubic double perovskites have drawn a lot of attention for their commercial use in optoelectronic and photovoltaic devices. Here we have explored the structural, electronic, optical and mechanical properties of lead-free non-toxic inorganic metallic halide cubic double perovskite Cs₂AgBiBr₆ in its ordered and disordered forms using first-principles density functional theory (DFT) to verify the suitability of its photovoltaic and optoelectronic applications. The indirect bandgap of Cs₂AgBiBr₆ is tuned to a direct bandgap by changing it from an ordered to disordered system following the disordering of Ag⁺/Bi³⁺ cations by creating antisite defects in its sublattice. In the disordered Cs₂AgBiBr₆, the Bi 6p orbital modifies the conduction band significantly and leads to a shift the conduction band minimum (CBM) from L to Γ-point. Consequently, the system changes from indirect to direct band gap material. At the same time the band gap reduces significantly. The band gap of Cs₂AgBiBr₆ decreases from 2.04 eV to 1.59 eV. The absorption edge towards the lower energy region and strong optical absorption in the visible to the UV region indicate that the disordered direct band gap material Cs₂AgBiBr₆ is appropriate for use in solar cells and optoelectronic and energy harvesting devices. Dielectric function, reflectivity and refractive index of disordered direct band gap material Cs₂AgBiBr₆ is favorable for its optoelectronic and photovoltaic applications. However, its stability and ductility favor its thin film fabrication. The creation of antisite defects in the sublattice of double perovskites opens a new avenue for the design of photovoltaic and optoelectronic materials.

The bandgap of Cs₂AgBiBr₆ is tuned to a direct bandgap by the disordering of Ag⁺/Bi³⁺ cations, creating antisite defects. The creation of antisite defects in the sublattice of double perovskites opens a new avenue for the design of photovoltaic and optoelectronic materials.

Thermodynamic and dynamic stability in a new potential Cs2AgAsCl6 perovskite: insight from DFT study

A schematic diagram of the possible energy band level for photocatalytic activity: (a) favorable energy band level, (b) unfavorable VBM, and (c) unfavorable CBM position.

The effect of metal substitution in CsSnI3 perovskites with enhanced optoelectronic and photovoltaic properties

Non-toxic lead-free halide metal perovskites have gained significant interest in photovoltaic and optoelectronic device applications. In this manuscript, we have studied the structural, electronic, mechanical, and optical properties of eco-friendly cubic CsSn_1-x Cu _x I₃, (x = 0, 0.125, 0.25, 0.5, 1) perovskites applying first-principles pseudopotential-based density functional theory (DFT). Cu-doped CsSnI₃ has a large impact on the band gap energy viz. the transition of direct band gap towards the indirect band gap. The mechanical properties demonstrate that the pristine and Cu-doped CsSnI₃ samples are mechanically stable and their ductility is enhanced by Cu doping. The mechanical stability and ductility favors the suitability of pure and Cu-doped samples in the thin film industry. The absorption edge of Cu-doped CsSnI₃ moves towards the lower energy region in comparison with their pure form. In addition, the high dielectric constant, high optical absorption, and high optical conductivity of Cu-doped CsSnI₃ materials suggests that the studied materials have a broad range of applications in optoelectronic devices, especially solar cells. A combined analysis of the structural, electronic, mechanical and optical properties suggests that CsSn_1-x Cu _x I₃, (x = 0, 0.125, 0.25, 0.5, 1) samples are a suitable candidate for photovoltaic as well as optoelectronic device applications.

Semiconductor to metallic transition under induced pressure in Cs2AgBiBr6 double halide perovskite: a theoretical DFT study for photovoltaic and optoelectronic applications

Inorganic double halide perovskites have a wide range of applications in low-cost photovoltaic and optoelectronic devices. In this manuscript, we have studied their structural, electronic, mechanical and optical properties using density functional theory (DFT) simulations. In this work, hydrostatic pressure is induced from 0 to 50 GPa. Disordered Ag and Bi atoms have a large impact on band gap energy; in this case, the indirect band gap is transferred towards a direct band gap. We have seen that pressure-driven samples have transformed a band energy semiconductor into a metallic one. Under the induced hydrostatic pressure, the covalent bond is transformed into a metallic bond and the bond lengths are reduced. Meanwhile, pressure-induced samples enhance symmetry breaking in [AgBr₆]⁵⁻ and [BiBr₆]³⁻ octahedra, which reduces the density of states of the Fermi surface and lowers the total energy. The mechanical behaviors demonstrated that the studied materials are mechanically stable as well as ductile and their ductile nature is enhanced by the driving pressure. The absorption peak is shifted towards the low energy region with increased hydrostatic pressure. The absorptivity and dielectric constant values are also increased with driving pressure. Phase transformed double halide perovskites triggered by outside stimuli produce several outstanding materials properties, giving great scope for a broad range of applications. This type of pristine and disordered double halide perovskite with pressure-driven semiconductor-to-metal phase transition samples may have potential applications in optoelectronic and photovoltaic devices.

Inorganic double halide perovskites have a wide range of applications in low-cost photovoltaic and optoelectronic devices.

Cu-Doped SnO₂ Nanoparticles: Synthesis and Properties

In this work, a simple, co-precipitation technique was used to prepare un-doped, pure tin oxide (SnO₂). As synthesized SnO₂ nanoparticles were doped with Cu₂₊ ions. Detailed characterization was carried out to observe the crystalline phase, morphological features and chemical constituents with opto-electrical and magnetic properties of the synthesized nanoparticles (NPs). X-ray diffraction analysis showed the existence of crystalline, tetragonal structure of SnO₂. Both the sample synthesized here showed different crystalline morphology. The band gap energy (E_g) of the synthesized sample was estimated and it was found to decrease from 3.60 to 3.26 eV. The band gap energy reduced due to increase in Cu₂₊ dopant amount inside the SnO₂ lattice. Optical properties were analyzed using absorption spectra and Photoluminescence (PL) spectra. It was observed that Cu₂₊ ions incorporated SnO₂ NPs exhibited more degradation efficiencies for Rhodamine B (RhB) dye compared to un-doped sample under UV-Visible irradiation. The dielectric characteristics of un-doped, pure and Cu₂₊ incorporated SnO₂ nanoparticles were studied at different frequency region under different temperatures. The ac conductivity and impedance analysis of pure and Cu₂₊ incorporated SnO₂ nanoparticles was also studied. The magnetic properties of the synthesized samples were analysed. Both the sample showed ferromagnetic properties. The research indicated that the Cu₂₊ ions doping can make the sample a promising candidate for using in the field of optoelectronics, magneto electronics, and microwave devices.

2-[(E)-2-(4-Methoxyphenyl)ethenyl]-1-methylpyridinium iodide

In the title mol­ecular salt, C₁₆H₁₀NO⁺·I⁻, the dihedral angle between the pyridinium and benzene rings is 6.61 (8)°. In the crystal, the cation is linked to the anion by a C—H⋯I inter­action arising from the activated aromatic C atom adjacent to the N⁺ cation.

4-Fluoro-N-[(E)-3,4,5-trimethoxybenzylidene]aniline

The title compound, C₁₆H₁₆FNO₃, exists in a trans configuration with respect to the C=N bond [1.258 (2) Å]. The central meth­oxy O atom deviates from the plane of the attached benzene ring by 0.0911 (14) Å. The dihedral angle between the aromatic rings is 47.58 (11)°. The crystal structure features C—H⋯N and C—H⋯O inter­actions.

Optical and electrical characteristics of pure CdS thin Films for different thickness

Conventional spray pyrolysis technique was employed for the preparation of cadmium sulphide (CdS) thin films that deposited onto glass substrates at 573 K from cadmium acetate and thiourea precursor solution for different deposition time. The surface morphology, compositional study and optical properties of the films have been characterized by Scanning Electron Microscopy (SEM) attached with an EDX and UV spectroscopy, respectively. The SEM micrographs of deposited film showed uniform deposition over the substrate. The EDX spectra of CdS thin films revealed that films are stoichiometric. All the films demonstrated more than 70% transmittance at wavelengths longer than 600 nm. The optical absorption coefficient (?) of the CdS films was determined from transmittance spectra. For different thickness (110 - 250nm) of the films, the direct band gap was found in the range of 2.15~2.48 eV. Resistivity (?) of CdS thin films was measured in the temperature range of 300 to 550 K. Activation energy (?E) was found in the range from 0.047 to 0.078 eV. DOI: http://dx.doi.org/10.3329/jbas.v37i1.15678 Journal of Bangladesh Academy of Sciences, Vol. 37, No. 1, 33-41, 2013

N-[4-(Di-methyl-amino)-benzyl-idene]-4-methyl-aniline

The mol­ecules of the title compound, C₁₆H₁₈N₂, exists in a trans conformation with respect to the C=N bond [1.270 (3) Å]. The least-squares plane of the di­methyl­amino group makes a dihedral angle of 1.3 (2)° with the ring to which it is attached. The dihedral angle between the two aromatic rings is 11.70 (2)°. The crystal structure features weak C—H⋯π inter­actions.

(E)-4-[2-(4-Ethoxyphenyl)ethenyl]-1-methylpyridinium naphthalene-2-sulfonate

In the title salt, C₁₆H₁₈NO⁺·C₁₀H₇O₃S⁻, the substituents attached to the central C=C bond adopt a trans conformation and the benzene and pyridinium rings are nearly coplanar, making a dihedral angle of 6.01 (9)°. The crystal structure features weak C—H⋯O hydrogen bonds and C—H⋯π inter­actions .

Crystallization Of Zinc Sulphate Single Crystals And Its Structural, Thermal And Optical Characterization

Zinc sulphate (ZnSO4.7H2O), an inorganic material has been crystallized by an isothermal evaporation method. ZnSO4.7H2O is highly soluble in water and the solubility is found to be increased almost linearly with the increase of temperature. At room temperature around 34°C, the solubility was found to be 92.41 gm/50 ml. The FT-IR spectroscopy was performed on pure zinc sulphate crystals to identify the presence of functional groups. The grown crystals have been subjected to powder X-ray diffraction to determine the unit cell dimensions and the crystal structure. The lattice parameters are found to be, a = 9.9810 Å, b = 7.2500 Å and c = 24.2800 Å, respectively. The values were in good agreement with those of the reported values. The TGA and DTA study revealed that the grown crystals have good thermal stability. The UV-vis spectrum showed that the material has wide optical transparency in the Ultra-violet region. Key words: Isothermal evaporation; Crystatization; Zinc sulphate; Structural characterization DOI: http://dx.doi.org/10.3329/jbas.v35i2.9426 JBAS 2011; 35(2): 203-210

An Investigation on the Growth and Characterization of Thiourea Single Crystal Grown from Aqueous Solutions

Thiourea single crystals have been grown from aqueous solution by slow cooling technique. The stability of the saturated solutions of different pH values has been assessed by measuring the metastable zone width (MSZW) by a nucleation method. MSZW has been enhanced by the influence of pH of thiourea solution. The growth rate of the thiourea crystal along the c-direction [001] was found faster for the higher pH value of the solution. The structural, optical and mechanical properties of the grown crystals were characterized by FT-IR spectroscopy, UV-Vis spectroscopy and powder X-ray diffraction. FT-IR and UV-Vis spectra provide information about the presence of functional groups. The Vicker's micro-hardness study has been performed on the grown crystals and the results reveal the softening nature according to Onistch concept. The growth features of the thiourea crystals were observed by etching study. A hexagonal spiral growth was observed on the [001] faces of thiourea crystals.  DOI: 10.3329/jbas.v33i1.2951 Journal of Bangladesh Academy of Sciences, Vol. 33, No. 1, 63-70, 2009