Change In Optical Band Gap Research Articles

Simulation of Solar Cell Device Performance Based on Hydrogenated Microcrystal Silicon (µc-Si:H) With Finite Element Method (FEM)

The structure and thickness of the solar cell device layer have a big impact on how well the solar cell works. There for, the aim of this study was to examine how hydrogenated microcrystalline silicon solar cells’ thickness and device structure affected how well they work. Simulation or modeling of the structure in one dimension (1D) is used for the analysis. MATLAB programming was used to analyze the simulation result. The optical band gap changes due to the influence of the structure, therefore the thickness of the p-, I, and n layers are kept constant at 250 Å, 9000 Å, and 250 Å respectively. The results showed that the maximum performance is obtained at the optical band gap, Eci = 1,39 eV, and the resulting power is 0.063465 Watt. Whereas in the simulation of the effect of the thickness on the i-layer, the optical band gap is set to a constant value of Eci = 1,4 eV, while the thickness of the p-layer and n-layer is set to 250 Å. The results also indicate that the maximum performance is at the i-layer thickness of 9000 Å and the power generated is 0.063364 Watt.

MOF‐Derived Carbon Embedded NiO for an Alkaline Zn−NiO Electrochromic Battery

AbstractIn the era of intelligent automation, smart energy storage devices are highly sought after due to their capability to reveal their state of charge by a visual color change. In principle, this is typically obtained by integrating electrochromic materials which demonstrate a change in optical band gap during redox reactions as electrodes in batteries/supercapacitors. Among various electrochromic materials, transition metal oxides have received significant interests because of their natural abundance, good cycling stability and high electrochemical response. In this work, metal organic framework (MOF) derived carbon embedded NiO (NiO@C) demonstrates very fast switching speeds of ∼1.4 s for coloration and ∼3.5 s for bleaching with high coloration efficiency of ∼135.16 cm2/C. These aspects make MOF‐derived NiO@C a potential candidate to be integrated as a smart positive electrode in an alkaline zinc (Zn) battery to construct a rechargeable Zn−NiO electrochromic (EC) battery. The Zn−NiO EC battery delivers an average voltage of ∼1.84 V and demonstrates a specific capacity of ∼85.3 mAh/m2 at 0.1 mA/cm2 current density. It visually displays its energy storage level by changing its color from dark brown (charged state) to colorless (discharged state), making it a potential candidate in smart windows and energy storage displays.

Influence of the Iron as a Dopant on the Refractive Index of WO3.

Results on studies of pure tungsten oxide WO3 and 2, 3 and 4% Fe-doped WO3 grown on the sapphire substrates by reactive pulsed laser deposition technique are reported. From X-ray diffraction it results that the crystalline structures changed with the substrate temperature and the peaks diffraction having a small shift by the amount of Fe content in WO3 lattice was noticed. Scanning electron microscopy presented a random behavior of WO3 nanocrystallites size with substrate temperatures. In the presence of 2% Fe-doped WO3, the nanocrystallites size varied gradually from 60 nm to 190 nm as substrate temperature increased. The transmission spectra of the pure and 2, 3 and 4% Fe-doped WO3 films were obtained within the 300–1200 nm spectral range. The refractive index of WO3 and Fe-doped WO3 layers were calculated by the Swanepoel method. The refractive index of pure WO3 shows a variation from 2.35–1.90 and for 2% Fe-doped WO3 from 2.30–2.00, as the substrate temperature increased. The contents of 3 and 4% Fe-doped WO3 presented nearly identical values of the refractive index with pure and 2% Fe-doped WO3, in error limits, at 600 °C. The optical band gap changes with substrate temperature from 3.2 eV to 2.9 eV for pure WO3 and has a small variation with the Fe.

Structural, electrical transport and optical properties of doped La0.7Ca0.3MnO3 ceramics

In this study, we have investigated the structural, electrical transport and UV–Visible properties of polycrystalline La0.7Ca0.3−xKxMnO3 (x=0.0, 0.05, 0.10, 0.20) ceramic samples prepared by conventional solid-state reaction. The structure characterized by X-ray diffraction shows that the samples possess orthorhombic perovskite structure belonging to Pnma space group with some impurity for higher doping level (x=0.10, 0.20) and cell volume is enlarged with Ca2+ substitution by K1+. The surface morphology was investigated by field emission scanning electron microscope, which indicates that the samples with better crystallization having higher density. The electrical transport properties were measured by the standard four-probe method, which demonstrates that the resistivity decreases non-monotonically and the metal–insulator transition temperature (TP) shifts to higher temperature with increasing K1+ content, the electrical transport behavior for metal and insulator region was explained using Zener double exchange model and small polaron hopping model respectively. Furthermore, the progressive substitution of Ca2+ by K1+ broadens the metal–insulator transition and reduces the temperature coefficient of resistivity. Room temperature UV–Vis studies show that the optical band gap changes with the partial replacement of Ca2+ with K1+. The investigations clearly show the effect of impurity present on structural, electrical transport and UV–visible response of the prepared ceramic samples.

Effect of annealing temperature on the structure and optical properties of Mn doped ZnS thin films

ZnS:Mn thin films were prepared by pulsed laser deposition (PLD), and annealed at 300°C, 400°C and 500°C. The effects of annealing temperature on the structure, morphology and optical properties of ZnS:Mn thin films were studied in detail. With the increase of annealing temperature, the intensity of main diffraction peak β-ZnS (111) increases, and the grain size of ZnS:Mn films grows larger, along with the film surface becoming rough and uneven. When the annealing temperature rises from 300°C to 500°C, the luminescence peak intensity of ZnS:Mn films located around 600 nm in the PL spectra enhances, with a peak blueshift from 610 nm to 595 nm. The annealing temperature can also affect the transmittance of the films and therefore change its optical band gap. With the increase of annealing temperature, the average transmittance decreases first and then increases, and the optical band gap changes as well.

Europium (Eu3+) - doped ZnO nanostructures: Synthesis, characterization, and photocatalytic, chemical sensing and preliminary assessment of magnetic properties

We have successfully synthesized single-phase wurtzite hexagonal ZnO:Eu3+ (1, 5 and 10 mol %) nanoparticles via facile co-precipitation method. The samples have been characterized by powder X-ray diffraction (PXRD), field-emission scanning electron microscopy (FESEM), energy dispersive spectroscopy (EDS), fourier transform infrared (FTIR) and UV–visible spectroscopy. Change in optical band gap is explained by invoking the existence 4f electronic states of Eu3+ in the band gap of ZnO. Photocatalytic performance of these samples for degradation of methyl orange (MO), rhodamine B (Rh B) and picric acid (PA) under UV illumination is found to be 3–3.5 times higher than pure ZnO. However, 5 mol% doping exhibited the highest catalytic efficiency. This sample was also highly sensitive and selective for PA, and the limit of detection was: 1.790 μM, 1.140 μM and 1.751 μM for 1, 5 and 10 mol% Eu3+ doped ZnO samples respectively. Finally, all samples behave weak ferromagnetically at room temperature, but a systematic increase in the ferromagnetic-like response is noticed with Eu3+ concentration, despite finding no evidence of secondary magnetic phases; EuO and Eu2O3 from XRD measurements. Conceivably, the observed ferromagnetic order is attributed to defect induced f7– ferromagnetism. Indeed, low concentration of Eu3+ dopant is found to be more significant, as reported by different groups.

Effect of Ni Doping on the Structural and Optical Properties of ZrO2 Thin Films

Transparent thin films of pure and nickel-doped ZrO2 with doping levels of 0, 1, 3 and 5 molar percentage were deposited through sol–gel dip coating and subsequently annealed at 500°C. Surface morphology and film thickness were examined through field emission scanning electron microscopy, which revealed a smooth surface morphology of the synthesized film, while elemental dot-mapping confirmed uniform distribution of nickel in the film. X-ray diffraction analysis revealed tetragonal crystalline structure of the deposited films. The structure exhibited a change in crystallite size upon varying the doping concentration. UV–Visible spectroscopy was employed for determining the optical band gap and transmittance. All the specimens were found to exhibit transmittance above 80%. Surface defects and oxygen vacancies were analyzed through photoluminescence spectroscopy. The photoluminescence peak intensities were observed to decrease upon increasing the nickel doping beyond 1% molar ratio, which was found to be in accordance with the change in optical band gap determined through UV–Visible spectroscopy. Fourier transform infrared spectroscopy revealed a strong absorption peak corresponding to Zr–O vibrational mode, while another peak corresponding to Ni–O vibrational mode was observed for nickel-doped samples, thereby implying replacement of some Zr4+ ions by Ni2+ ions in the lattice.

Formation of high performance nanostructured ZnO thin films as a function of annealing temperature: structural and optical properties

Zn thin films are deposited on quartz substrate by DC magnetron sputtering method under the same condition. Then, ZnO nanoparticles are produced by heating Zn thin films in the open air at temperatures of 300, 500, 700, 900, and 1100°C for 2 hours. XRD analysis of these films shows that except for the 1100-ZnO sample, which has a cubic structure, the rest of the films confirm the hexagonal crystal structure of the Wurtzite. An examination of the ultraviolet spectrum and the calculation of optical parameters also indicate that annealing temperature is an influential factor on optical properties of high-quality ZnO thin films. Also, changes in optical energy bandgap of the samples correspond to the Burstein-Moss theory. Examination of the spectrum of photosynthesis through severe exciton emission demonstrates a minor defect in ZnO nanoparticles prepared this way. In general, findings indicate that physical properties of ZnO thin films are affected by annealing temperature, and among the samples, 700-ZnO sample displays the optimum optical and structural properties.

Effect of vacuum thermal annealing on optical properties of amorphous (Se80Te20)94Ag6 chalcogenide thin films prepared by thermal evaporation technique

Amorphous (Se80Te20)94Ag6 thin films are prepared at room temperature by using thermal evaporation technique. The as-prepared thin films are annealed both at higher and lower temperatures than glass transition temperature Tg. X-ray diffraction of annealed film above Tg confirms the presence of different phases. The glass transition temperature of as-prepared glass is evaluated with the help of DSC measurement. Transmittance measurements are used to find the value of optical parameters and optical band gap Eg. Refractive index and extinction coefficient increases with increase in annealing temperature. The band gap show an increase for the annealing temperature less than Tg and decrease for the temperature greater than Tg. Mott and Davis Model forms the basis for the explanation of change in optical band gap.

Crystal growth, finite element analysis and oxygen annealing of ZnO bulk crystal grown by low-temperature-gradient chemical vapor transport

The growth of high-quality ZnO bulk crystals is an outstanding challenge, and the nature of grown-in defects in crystals is far from well understood. In this work, a specially designed low-temperature-gradient CVT growth system was developed based on finite element analysis. High-quality ZnO single crystals were successfully grown. The supersaturation front in the growth system was controlled, and internal stress in the crystal was reduced by introducing a radiation baffle and a special seed pedestal. The structural, electrical, and optical properties of ZnO crystals were studied before and after oxygen annealing. The scanning electron microscope (SEM) and optical microscope (OM) results indicate the stable growth is achieved under the Zn-rich growth condition. The X-ray rocking curve measurements reveal the high crystalline quality of the grown crystal with the full-width at half-maximum (FWHM) value of 17 arcsec for the (004) reflection. The time-of-flight secondary ion mass spectroscopy (ToF-SIMS) results prove the high purity of grown crystals and reveal the variations of trace impurity concentrations in crystals. When annealed in oxygen at 1000 °C, the optical band gap (Eg) changes from 2.50 eV to 3.15 eV. The Raman analysis indicates that oxygen vacancies (Vo) in the as-grown crystal disappear after annealing. The Hall measurements show that the room temperature (RT) mobilities before and after annealing are 197 cm2V−1c−1 and 207 cm2V−1c−1, respectively. The RT carrier concentration decreases by about two orders of magnitude to 5.45 × 1015 cm−3, while the RT resistivity increases by about one order of magnitude to 5.57 Ω cm after annealing. The positron annihilation lifetimes (PALS) results prove the presence of Zn vacancies (Vzn) after annealing. The origins of as-grown ZnO green luminescence (GL) and the temperature-dependent blue shifts of the GL peak positions are explained based on Zni and Vo defects. The fine structures of annealed ZnO GL are found to be related to Vzn native defects rather than Cu impurity.

Preparation of Cu3N/MoS2 Heterojunction through Magnetron Sputtering and Investigation of Its Structure and Optical Performance.

Cu3N/MoS2 heterojunction was prepared through magnetron sputtering, and its optical band gap was investigated. Results showed that the prepared Cu3N/MoS2 heterojunction had a clear surface heterojunction structure, uniform surface grains, and no evident cracks. The optical band gap (1.98 eV) of Cu3N/MoS2 heterojunction was obtained by analyzing the ultraviolet-visible transmission spectrum. The valence and conduction band offsets of Cu3N/MoS2 heterojunction were 1.42 and 0.82 eV, respectively. The Cu3N film and multilayer MoS2 formed a type-II heterojunction. After the two materials adhered to form the heterojunction, the interface electrons flowed from MoS2 to Cu3N because the latter had higher Fermi level than the former. This behavior caused the formation of additional electrons in the Cu3N and MoS2 layers and the change in optical band gap, which was conducive to the charge separation of electrons in MoS2 or MoS2 holes. The prepared Cu3N/MoS2 heterojunction has potential application in various high-performance photoelectric devices, such as photocatalysts and photodetectors.

Facile synthesis, structure analysis and optical performance of manganese oxide-doped PVA nanocomposite for optoelectronic and optical cut-off laser devices

In the present work, successful manganese oxide (Mn2O3) nanoparticles (NPs) were synthesized by a combustion technique, while the casting process was employed for the manufacturing of polymer nanocomposites with various weights of Mn2O3 based on Poly(Vinyl Alcohol), PVA. Multiple methods such as X-ray diffraction (XRD), HR-TEM, EDAX, EDS, SEM, FT-IR, DTA analysis, optical spectroscopy from UV to IR regions, and optical reduction (CUT-OFF) setup were used to characterize the structural, elemental chemical analysis, morphological, optical properties, and cut-off laser characteristic of nanocomposite samples. Mn2O3 nanoparticles have a crystallite size of 22.08 nm as calculated using the Debye–Scherer formula from XRD, while the HR-TEM shows a spherical particle of size 30–38 nm range. EDAX spectra and EDS mapping were used to detect the elemental particles of the nanocomposite. The external morphology of the films by SEM images shows an increase in the agglomeration size of the cluster with the percentage of Mn2O3 nanoparticles in PVA. FT-IR spectra show excellent incorporation between the matrix of polymer and the Mn2O3 via the hydroxyl group. Moreover, with increasing the doping rate of nanoparticles, the thermal stability of PVA increased. A significant change of optical transmittance, absorption edge, Urbach energy, and transition bandgap have been observed due to the influence of Mn2O3. The comparison between the bandgap values that have been estimated from Tauc’s relation and thus resulting from optical dielectric loss indicates a direct allowed transition of electrons in the nanocomposites. The light is entirely UV–Vis absorbed by PVA with a high percentage of Mn2O3 nanoparticles. Moreover, the efficiency of the films to decrease the power of two laser beams (635 nm and 533 nm) has been observed. The flexible films of PVA with an elevated rate of Mn2O3 are considered a successful option for low-cost technologies of optical limiting.

Growth and characterization of Ag-Cu2O thin films: DC magnetron sputtering method

Silver (Ag) doped copper oxide (Cu2O) thin film layers on glass slides were coated using a reactive magnetic technique under the variation of substrate temperature. Microstructure of the deposited layers was analyzed using X-ray diffractometry, SEM and FTIR studies. From the characterization of as deposited Ag-Cu2O thin films, it was revealed that the thin layers coated at deposition temperature, 100 °C shows a characteristic diffraction peak at 2θ = 36.4° which was also followed by SEM and EDAX studies. FTIR spectrum analysis describes that the decreases of C-H stretching modes with increasing the temperature and estimated the relation between sp3 and sp2 hybridization. The change in optical band gap between undoped and doped Ag-Cu2O film was also observed. The present paper explains the structural properties of as deposited films to understand the influence of the photovoltaic behaviour.

Tailoring light-matter interaction in WS2 –gold nanoparticles hybrid systems

Recently, considerable attention has been paid to tune the emission using hybrid systems composed of layered transition-metal dichalcogenides and metal nanoparticles (NPs) since metal NPs have the ability to enhance and localize the incident electromagnetic field. Furthermore, these hybrid systems show great interest from the standpoint of fundamental science as it constitutes an atomic scale prototype of charge-transfer complexes. Here, we realized ${\mathrm{WS}}_{2}$--gold (Au) NPs hybrids by chemically growing Au NPs at the edges of the mechanically exfoliated bilayer ${\mathrm{WS}}_{2}$. The Au NPs significantly increase the light-matter interaction which has been studied through Raman and photoluminescence (PL) spectroscopy. A substantial enhancement of the PL intensity in the ${\mathrm{WS}}_{2}$--Au composite concerning the pristine ${\mathrm{WS}}_{2}$ has been observed, and it increases as the number and size of the Au NPs on ${\mathrm{WS}}_{2}$ is increased. Geometry-dependent modification of plasmon resonance energy of Au NP alters the coupling strength between the emission pathways of ${\mathrm{WS}}_{2}$ and the plasmon which is manifested by a change in relative intensity between trion $({X}^{\ensuremath{-}})$ and exciton $(X)$ emissions. We probe the mechanism of the PL intensity modulation through polarization-dependent measurements and simulation. We have demonstrated that, in ${\mathrm{WS}}_{2}$, the internal quantum efficiency increases and activation energy decreases due to coupling with Au NPs. Compared to pristine ${\mathrm{WS}}_{2}$, a faster change in optical band gap with temperature in ${\mathrm{WS}}_{2}$--Au may be due to enhancing electron-phonon interaction and lattice expansion in the latter. Our paper indicates the possibility to develop high performance transition-metal dichalcogenide-based photonic devices.

Characterization Studies of Reduced Graphene Oxide/Zinc Oxide Nanocomposites Synthesized by Hydrothermal Method

Reduced graphene oxide/zinc oxide (RGO/ZnO) nanocomposites were synthesized by facile hydrothermal method; this method consists of exfoliation of graphite with modified Hummer's method and synthesis of (RGO/ZnO) nanocomposites using hydrothermal method. X-ray diffraction, TEM and FT-IR spectroscopy were used for structure morphological characterization. Optical properties of the samples were studied by measuring their optical absorbance. It can be concluded from XRD analysis that there are improvements of crystallinity associated with the increase of the crystallite size, as well as the increase in both of the (Zn-O) bond length and unit cell volume with the increase of ZnO ratio in RGO/ZnO nanocomposites. The morphological studies confirmed that the scale of ZnO particles is large and the size distribution is not uniform in samples of RGO/ZnO and that most particles have average size of about 9 nm while some particles even have larger size. The optical absorption spectra show that the excitonic peak of the as-prepared samples is red shifted from 268 nm to 376 nm for reduced grapheme oxide (RGO) with the increase of ZnO ratio, and the optical band gap changes from 2.39 for pure RGO to 3.34 eV for pure ZnO. The effect of UV irradiation on the optical absorption nanocomposites at different UV doses was carried out using UV lamp.

Composition dependent structural phase transition and optical band gap tuning in InSe thin films

Bulk alloys of InxSe100-x (x = 5, 10, 20, 30, 40 and 50) are prepared using melt quenching technique. Thin films having thickness ~750 nm of these prepared bulk alloys are fabricated using thermal evaporation technique on glass substrate. The as-deposited InxSe100-x thin films with x ≤ 40 are amorphous and In50Se50 thin film is crystalline in nature verified from X-ray diffraction (XRD). The change in morphology of deposited thin films with indium content also verifies structural phase transition and found that the phase transition started with x = 40 which is not detected in XRD pattern. The drastic change in transmission is found with 50% indium content. In50Se50 thin film has less than 30% transmission whereas other films are highly transparent. Optical band gap is calculated using Tauc's plot and decrease in optical band gap is observed with indium content. The variation of optical band gap from 1.88 eV to 1.12 eV is achieved with indium content of 5%–50%. The structural transition and change in optical band gap depict that InSe thin films are potential candidates in various technological applications.

Temperature Driven Phase Transition of Organic-Inorganic Halide Perovskite Single Crystals

Organic-inorganic halide perovskite single crystals undergo phase transition of being cubic, tetragonal, or orthorhombic depending on the temperature. We investigated the CH3NH3PbBr3−xIx single crystals grown by the inverse temperature crystallization method with temperature-dependent UV-Vis absorption and photoluminescence. From the temperature-dependent absorption measurement, the optical band gap is extracted by derivation of absorption spectrum fitting and Tauc plot. In our results, CH3NH3PbBr3−xIx single crystals show that an abrupt change in optical band gap, PL peak position and intensity appears around 120 K - 170 K regions, indicating the phase transition temperature.

Photo and thermally induced properties change in Bi/Ag/Se trilayer thin film

ABSTRACTIn this article, we have demonstrated the optical and structural properties change in Bi/Ag/Se trilayer thin films by the influence of thermal and photon energy. The trilayer films prepared by thermal evaporation technique were annealed and laser irradiated at room temperature. The X-ray diffraction study revealed the Ag2Se phase formation and the surface morphology change is being studied by Field emission scanning electron microscopy. The optical properties of the studied films were characterized by using FTIR spectrophotometer in the wavelength range 400–1200 nm. The reduction of optical band gap by both thermal and laser irradiation is being discussed on the basis of chemical disorderness, defect states and density of localized states in the mobility gap. The Raman shift due to annealing and irradiation supports the changes in the film. The large change in optical band gap in thermal annealing is useful for memory device and waveguide fabrication.

Low temperature synthesis of graphitic carbon nitride nanorods for heavy metal ions sensing

In the present work synthesis of different morphologies of graphitic carbon nitride (GCN) including both one dimensional rod-like as well as two dimensional sheet-like structures through simple chemical route have been reported. The as-prepared samples are used to detect the presence of different transition/heavy metals like copper, iron, nickel, lead etc. that have acute negative impact on human health causing diseases like cancer, Alzheimer's diseases, Parkinson's disease, gastrointestinal irritations etc. The rod and sheet like morphology of the samples was confirmed from FESEM and TEM analysis. The samples were characterized by XRD and FTIR to provide a detail insight into the phase formation and the different bonds present in the samples. Change in optical band gap of the samples was calculated from diffuse reflectance spectroscopy. Photoluminescence Spectroscopy was performed to study the change in the emission spectrum with the change in the morphology of GCN. Detection of different heavy/transition metals was done by the means of fluorescence spectroscopy. It has been shown that the as prepared samples are most effective in detection of Cu2+ ions over others and thus the corresponding sensing mechanism has been studied in much detail.

Aggregation induced enhanced emission of diphenylamine and pyridine based conjugated organic materials

Aggregation induced emission enhancement (AIEE) was studied for diphenylamine and pyridine based donor–acceptor conjugated moieties (DPA-PA-1-3). These moieties were synthesized from Knoevenagel condensation and great solubility in organic solvents such as toluene, tetrahydrofuran, ethyl acetate, dichloromethane, chloroform etc due to various alkyl chains. AIEE process was investigated from absorption/fluorescence spectroscopy and scanning electron microscopy. The absorption maximum of DPA-PA-1-3 appeared at 437, 433, 444 nm in THF solution. The optical band gaps are 2.33, 2.29, and 2.25 eV calculated from thin film absorption edges. After aggregation using different water fractions, the absorption of conjugated moiety was red shifted to 12 nm (j-aggregation) and there was no change in optical band gap. The photoluminescence spectra of three molecules were exhibited a maximum peak at 511, 515, 529 nm with greenish fluorescence in chloroform solution and 553, 541, 554 nm as in thin film state. DPA-PA-1-3 showed a delay fluorescence decay time (τ1) of 35, 16 and 14 µs respectively. Aggregation-induced emission (AIE) phenomenon of DPA-PA-1-2 was also observed and fluorescence intensity was enhanced with different water fractions. The lower electrochemical band gaps 1.90 and 1.80 eV was observed by cyclic voltammetry. The morphological images were indicated that spherically shaped particles were observed with lower surface roughness. These types of low bandgap materials have much attention for their various potential applications in optoelectronic devices.