Despite remarkable advances of perovskite materials, the stability issue hurdles in the path of commercial deployment of perovskite solar cell and optoelectronics devices. To overcome these, ...CH3(NH)2PbI3−xClx thin film is deposited by chemical spray pyrolysis (CSP) technique at a temperature of 125 °C under atmospheric conditions and then CH3(NH)2 free Cs based in the form of CsPbI3−xClx is synthesized. The precursor solution shows turbid in nature which became transparent slowly, and after 60 min stirring it became highly transparent that insights crystallization formation for the thin film growth. SEM images exhibit the thin films are pinholes free with grains size (Ave. ∼2 µm) of FAPbI3−xClx are larger enough than that of CsPbI3−xClx. The high crystalline property with pinhole-free surfaces are prerequisite for high performance optoelectronic devices applications. Coexistence mixed phases are observed in XRD patterns could be due to decomposition and/or incomplete reaction of the phases. The thin films exhibit cubic and orthorhombic crystal structures. Grains size and lattice parameters calculations are demonstrated that the films are micro-nanostructures, and their size strongly depends on the films constituents. Band gap can be tuned in between 1.70. eV and 1.62 eV. The solar cell performance was investigated using SCAPS-1D software and the obtained efficiency is to be η = 12.29% of FAPbI3−xClx is coherent with reported results, whereas of CsPbI3−xClx is to be η = 11.15%. From the theoretical photocatalytic calculation, it can be concluded that FAPbI3−xClx may be suitable for O2 production, but CsPbI3−xClx is an efficient candidate for photocatalytic process in the visible region due to nearly equal effectiveness both of the oxidation and reduction processes. Thus, CsPbI3−xClx as a new candidate perovskite for solar cell and photocatalytic applications, requires further attention.
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•Experimentally deposited CH3(NH)2PbI3−xClx thin films at atmospheric conditions CsPbI3−xClx.•Band gap can be engineered in between 1.70.70 eV and 1.62 eV.•Cs atom can hinder the grain size growth of CH3(NH)2PbI3−xClx.•SCAPS-1D software exhibited the efficiency to be η = 12.29% and 10.84% for FAPbI3−xClx and CsPbI3−xClx.•CsPbI3−xClx is an efficient candidate of photocatalytic process for oxidation and reduction processes.
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
Hydrostatic pressure dependent structural, electronic, elastic and optical properties of Heusler compounds Cr2YAl (Y=Mn, Co) are investigated by the first-principles calculations. Present study shows ...good agreement between the calculated and experimental values of lattice parameters of these compounds. The gradual decrease of lattice parameter and unit cell volume with the increase of pressure eliminates the possibility of phase transition up to the considered pressure range 0–30 GPa. The absence of negative frequency in the phonon dispersion curves at various external pressures up to 30 GPa confirm the dynamical stability of these compounds. The values of Pugh's ratio, Poisson's ratio and Cauchy pressure indicate the ductility of Cr2CoAl while those criteria confirm the brittleness of Cr2MnAl. Pressure dependent behaviour of the elastic constants of these compounds shows the mechanical stability over the studied pressure range (0–30 GPa). Crystal stiffening of both the compounds is indicated by the increase of Debye temperature with increasing hydrostatic pressure. The pressure dependent band structure and density of states (DOS) calculations reveal the half- and the near half-metallic behaviour of Cr2MnAl and Cr2CoAl, respectively up to 20 GPa while those disappears at pressure around 30 GPa. The variations of optical constants with pressure is consistent with the results of the electronic structure calculations. High reflectivity (>45%) of both the compounds makes them attractive for optoelectronic device applications.
Heusler compound, First-principles calculations, Elastic constants, Electronic properties, Half-metal.
Abstract
In this paper we explain the temperature dependence of excitonic effective mass and charge carrier conduction mechanism occurs in CH
3
NH
3
PbI
3−x
Cl
x
thin films prepared by chemical dip ...coating (CDC), spray pyrolysis (Spray) and repeated dipping-withdrawing (Dipping). Hall Effect study confirmed that prepared CH
3
NH
3
PbI
3−x
Cl
x
samples are p-type semiconductor having carrier concentration of the order of ~ 10
16
cm
−3
. The charge carrier mobility, mean free path and mean free life time were found to decrease with increasing temperature due to polaronic effect. The excitonic effective mass is estimated to (0.090–0.196)m
e
and excitonic binding energy (15–33) meV, well consistent with Wannier-Mott hydrogenic model and the nature of exciton is likely to be Mott-Wannier type. From electrical measurement, it was observed that charge carrier conduction in CH
3
NH
3
PbI
3−x
Cl
x
is governed by migration of
$${\mathrm{I}}^{-}$$
I
-
and CH
3
N
$${\mathrm{H}}_{3}^{+}$$
H
3
+
vacancies and vacancy-assisted diffusion processes depending on temperature.
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•Nanorods like crystalline CH3NH3PbI3-xClx thin film at an ambient atmosphere by spray deposition.•High absorption coefficient with a band gap of 1.64 eV.•Structural phase transition ...from tetragonal (at RT) to orthorhombic (at 80 K).•Generation of second harmonic emission.
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.
Abstract
Using new ultraviolet (UV) spectra of five background quasars from the Cosmic Origins Spectrograph on the Hubble Space Telescope, we analyze the low-latitude (
) regions of the Fermi ...Bubbles, the giant gamma-ray-emitting lobes at the Galactic Center. We combine these data with previous UV and atomic hydrogen (H
i
) data sets to build a comprehensive picture of the kinematics and metal column densities of the cool outflowing clouds entrained in the Fermi Bubbles. We find that the number of UV absorption components per sight line decreases as a function of increasing latitude, suggesting that the outflowing clouds become less common with increasing latitude. The Fermi Bubble H
i
clouds are accelerated up to
b
∼ 7°, whereas when we model the UV Fermi Bubbles clouds’ deprojected flow velocities, we find that they are flat or even accelerating with distance from the Galactic center. This trend, which holds in both the northern and southern hemispheres, indicates that the nuclear outflow accelerates clouds throughout the Fermi Bubbles or has an acceleration phase followed by a coasting phase. Finally, we note the existence of several blueshifted high-velocity clouds at latitudes exceeding ∼30°, whose velocities cannot be explained by gas clouds confined to the inside of the gamma-ray-defined Fermi Bubbles. These anomalous-velocity clouds are likely in front of the Fermi Bubbles and could be remnants from past nuclear outflows. Overall, these observations form a valuable set of empirical data on the properties of cool gas in nuclear winds from star-forming galaxies.
Using plane-wave pseudopotential density functional theory (DFT), the first-principle calculations are performed to investigate the structural aspects, mechanical behaviors and electronic features of ...the newly synthesized CaAl2Si2-prototype intermetallic compound, MgAl2Ge2 for the first time and the results are compared with those calculated for its silicide and carbide counterparts MgAl2Si2 and MgAl2C2. The calculated lattice constants agree fairly well with their corresponding experimental values. The estimated elastic tensors satisfy the mechanical stability conditions for MgAl2Ge2 along with MgAl2Si2 and MgAl2C2. The level of elastic anisotropy increases following the sequence of X-elements Ge → Si → C. MgAl2Ge2 and MgAl2Si2 are expected to be ductile and damage tolerant, while MgAl2C2 is a brittle one. MgAl2Ge2 and MgAl2Si2 should exhibit better thermal shock resistance and low thermal conductivity and accordingly these can be used as thermal barrier coating (TBC) materials. The Debye temperature of MgAl2Ge2 is lowest among three intermetallic compounds. MgAl2Ge2 and MgAl2Si2 should exhibit metallic conductivity; while the dual characters of weak-metals and semiconductors are expected for MgAl2C2. The values of theoretical Vickers hardness for MgAl2Ge2, MgAl2Si2, and MgAl2C2 are 3.3, 2.7, and 7.7 GPa, respectively, indicating that these three intermetallics are soft and easily machinable.
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•The structural, mechanical and electronic properties of three intermetallics are calculated.•MgAl2Ge2 and MgAl2Si2 are ductile and damage tolerant, while MgAl2C2 is a brittle one.•MgAl2Ge2 and MgAl2Si2 can be used as thermal barrier coating (TBC) materials.•The studied three intermetallics are soft and easily machinable.
Synopsis CH3NH3PbI3-xClx crystalline film composed of cuboids and polyhedral structure was prepared by dipping and withdrawing method at ambient. X-ray diffraction shows the presence of tetragonal ...and cubic phases having high absorption coefficient of 106 m-1. Photoluminescence study confirms shallow and deep level emissions. Temperature dependent-cathodoluminescence shows a green luminescence at 2.51 eV accompanied by weak red and ultraviolet luminescence at 80 and 300 K.
The mixed halide CH
3
NH
3
PbI
3−x
Cl
x
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 CH
3
stretching/bending of C–H bond in CH
3
NH
3
PbI
3−x
Cl
x
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 CH
3
NH
3
PbI
3−x
Cl
x
thin film shows high spectral absorption coefficient of the order of 10
6
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
E
g
= 2.50 eV over tetragonal phase with band gap
E
g
= 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 CH
3
NH
3
PbI
3−x
Cl
x
thin film, suitable for preparation of light-emitting devices.
Heterojunction diodes of
n
-ZnO/
p
-Si (100) and
n
-ZnO:Al/
p
-Si (100) were fabricated by spray pyrolysis technique. X-ray diffraction (XRD), energy dispersive x-ray spectroscopy (EDX), and field ...emission scanning electron microscopy (FESEM) were used to characterize the as-prepared samples. The XRD pattern indicates the hexagonal wurzite structure of zinc oxide (ZnO) and Al-doped ZnO (AZO) thin films grown on Si (100) substrate. The compositional analysis by EDX indicates the presence of Al in the AZO structure. The FESEM image indicates the smooth and compact surface of the heterostructures. The current–voltage characteristics of the heterojunction confirm the rectifying diode behavior at different temperatures and illumination intensities. For low forward bias voltage, the ideality factors were determined to be 1.24 and 1.38 for un-doped and Al-doped heterostructures at room temperature (RT), respectively, which indicates the good diode characteristics. The capacitance–voltage response of the heterojunctions was studied for different oscillation frequencies. From the 1/
C
2
–
V
plot, the junction built-in potentials were found 0.30 V and 0.40 V for un-doped and Al-doped junctions at RT, respectively. The differences in built-in potential for different heterojunctions indicate the different interface state densities of the junctions. From the RT photoluminescence (PL) spectrum of the
n
-ZnO/
p
-Si (100) heterostructure, an intense main peak at near band edge (NBE) 378 nm (3.28 eV) and weak deep-level emissions (DLE) centered at 436 nm (2.84 eV) and 412 nm (3.00 eV) were observed. The NBE emission is attributed to the radiative recombination of the free and bound excitons and the DLE results from the radiative recombination through deep level defects.
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