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Correlation between the morphology and the opto-electronic and electrical properties of organometallic halide perovskite (CH<sub>3</sub>NH<sub>3</sub>MH<sub>3</sub>) thin films
摘要： Organometallic halide perovskites are emerging as a promising class of materials for optoelectronic applications. Crystal morphology is important for improving the organic-inorganic lead halide perovskite semiconductor property in optoelectronic, electrical and photovoltaic devices. It is thus important to investigate how the changes in crystal morphology affect the semiconductor behavior. This work presents a study that was carried out to assess the relationship between different deposition methodologies and the opto-electronic and electrical properties of the resultant organometallic halide perovskite thin films. Herein, single step solution deposition method and two step solution deposition methods have been used to deposit perovskite thin films. The structure and morphology of perovskite was controlled by changing concentration, annealing temperatures and dip coating times. From the study, prepared films showed different morphologies as the concentration, annealing temperatures and dip coating times were varied. Optical band gap energies of 2.23 eV, 2.13 eV and 2.09 eV were obtained for samples prepared by single step solution deposition method and 1.57 eV, 1.55 eV and 1.52 eV for two step solution deposition method. The sheet resistance values decreased with an increase in concentration, annealing temperatures and dip coating times. The decrease in optical band gap energy and sheet resistances are excellent properties for high performance photovoltaic devices.
关键词： Perovskite,sheet resistivity,activation energy,band gap,sheet resistance,spectroscopy
更新于2025-11-19 16:56:35
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Influence of bath temperatures on physical and electrical properties of potentiostatically deposited Cu2O thin films for heterojunction solar cell applications
摘要： In the present work, the influence of bath temperatures on structural, morphological, vibrational, optical, electrical and photo response properties of the electrochemically deposited cuprous oxide (Cu2O) thin films on fluorine doped tin oxide substrate is extensively investigated with the help of X-ray diffraction (XRD), scanning electron microscopy (SEM), Micro Raman spectroscopy, photo luminescence (PL) spectroscopy, UV–visible spectroscopy, LCR measurement, Keithley 4200 semiconductor characterization system respectively. XRD patterns reveal that the deposited Cu2O films have cubic structure grown along the preferential (111) orientation and the film deposited at 40 °C shows better crystalline nature when compared at 55 and 70 °C. The micro structural properties of films such as crystallite size (D), dislocation density (δ), micro strain (ε) and stacking fault probability (α) were calculated and discussed in detail. SEM displays a well-defined three side pyramid shaped morphology for the film deposited at 40 °C. Micro Raman and PL spectra reveal the film deposited at 40 °C by being better crystalline at a higher acceptor concentration. UV–Visible study shows that the optical energy band gap increases from 2.05 to 2.17 eV with an increase in bath temperature from 40 to 70 °C. The frequency-temperature dependence of impedance analysis shows a higher electrical conductivity for a film deposited at 40 °C compared to other bath temperatures. I-V measurement illustrates a good photoconductivity response for Cu2O thin film deposited at 40 °C compared to films deposited at 55 and 70 °C.
关键词： Micro Raman spectroscopy,X-ray diffraction,Photoconductivity,Cuprous oxide,Pyramid shape
更新于2025-11-19 16:46:39
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Electrical conductivity and conduction mechanisms in (Na <sub/>0.5</sub> Bi <sub/>0.5</sub> TiO <sub/>3</sub> ) <sub/>1?x</sub> (BiScO <sub/>3</sub> ) <sub/>x</sub> (0.00 ≤ <i>x</i> ≤ 0.25) solid solutions
摘要： The electrical properties of (Na0.5Bi0.5TiO3)1-x(BiScO3)x (NBT-BS, 0.00 ≤ x ≤ 0.25) solid solutions are established by ac impedance spectroscopy and electromotive force transport number measurements. The bulk conductivity decreases with increasing BS incorporation but the oxide-ion transport number remains high (≥0.85) over a wide compositional range 0.00 ≤ x ≤ 0.15 and drops to ≈0.7 for x ≥ 0.20. NBT-BS solid solutions can only present either predominant oxide-ion conduction or mixed ionic-electronic conduction behaviour, indicating that oxide-ion conduction cannot be fully eliminated by incorporation of BS. This is in contrast from our previous study where incorporation of ≈7% BiAlO3 (BA) can fully suppress the oxide-ion conduction in NBT. The conductivity–composition relationships of NBT-BS solid solutions are attributed to a competing effect from lattice expansion, which enlarges the channel for oxygen ion migration, with trapping between B-site acceptor ions, Sc'Ti, and oxygen vacancies, V??O, which decreases oxygen ion migration. Comparisons between NBT-BS, NBT-BA and NBT-BiGaO3 (BG) solid solutions suggest that small acceptor ions on the B-site are more effective in trapping oxygen vacancies and consequently more effective to suppress the oxide-ion conduction and thus reduce dielectric loss at elevated temperatures.
关键词： transport number,electrical conductivity,solid solutions,sodium bismuth titanate,oxide-ion conduction,conduction mechanisms,impedance spectroscopy,BiScO3
更新于2025-11-14 17:28:48
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Device simulation of Cu(In,Ga)Se2 solar cells by means of voltage dependent admittance spectroscopy
摘要： The simulation of solar cell devices is important for the understanding of defect physics and loss mechanisms in real solar cells. On the other hand, voltage dependent admittance spectroscopy delivers essential information for establishing a baseline simulation model of Cu(In,Ga)Se2 (CIGSe) solar cells. Here we give an explanation for the weak temperature dependence of the N1-signal, the latter being not compatible with a bulk defect or with a simple hole barrier at the Mo back contact. Furthermore, we find a Ed,IF – EV ≈ 0.3 eV deep recombination-active acceptor state at the absorber/buffer interface made of air-light exposed CIGSe absorbers. This gives us the ability to explain the reduction of power conversion efficiency of solar cells made from air-light exposed absorbers. From the voltage dependent capacitance step of this interface defect we can deduce the formerly unknown position of the Fermi level at the hetero junction in equilibrium which is close to mid-gap. Simulation of dark J-V curves allows a refinement of the parameter of this absorber/buffer interface defect, resulting in a defect density of Nd,IF ≈ 3.5·1011 cm-2 as well as capture cross sections of σn ≈ 4·10-16 cm2 for electrons and σp ≈ 3·10-11 cm2 for holes.
关键词： device simulation,Cu(In,Ga)Se2,admittance spectroscopy,defect physics,solar cells
更新于2025-11-14 17:28:48
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Electrical and optical properties of organic light-emitting diodes with rhenium(I) complexes using DC and AC methods
摘要： Four rhenium(I) tricarbonyl complexes with 1,10-phenanthroline and derivative bearing electron-donating CH3 and OCH3 substituents were doped into host material poly (9-vinylcarbazole) (PVK) with a mass ratio of 8% as the emissive layer in organic light-emitting diodes (OLEDs). All complexes showed photoluminescence in the solution and embedded into a PVK matrix (λmax～520–550 nm). The comparison with the bare PVK emission and the compound/PVK ?lm shows that the emission of the polymer was quenched through an energy transfer process from PVK to the dopant. The electrical properties of the devices with FTO/PEDOT:PSS/Complex:PVK/Al architecture were investigated using the DC method by curves of current density-voltage and the AC method as admittance spectroscopy, which showed that the behavior of the devices is controlled by charge carrier injection rather than bulk transport.
关键词： Energy transfer,Re(I) complexes,Charge injection,Admittance spectroscopy,Emission,OLEDs
更新于2025-11-14 17:28:48
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Reorientational dynamics of organic cations in perovskite-like coordination polymers
摘要： Here we report the dynamics of organic cations as guest molecules in a perovskite host-framework. The molecular motion of CH3NH3+ (MAFe), (CH3)2NH2+ (DMAFe) and (CH3)3NH+ (TrMAFe) in the cage formed by KFe(CN)63? units was studied using a combination of experimental methods: (i) thermal analysis, (ii) dielectric and electric studies, (iii) optical observations, (iv) EPR and 1H NMR spectroscopy and (v) quasielastic neutron scattering (QENS). In the case of MAFe and TrMAFe, the thermal analysis reveals one solid-to-solid phase transition (PT) and two PTs for the DMAFe crystal. A markedly temperature-dependent dielectric constant indicates the tunable and switchable properties of the complexes. Also, their semiconducting properties are confirmed by a dc conductivity measurement. The broadband dielectric relaxation is analyzed for the TrMAFe sample in the frequency range of 100 Hz–1 GHz. QENS shows that we deal rather with the localized motion of the cation than a diffusive one. Three models, which concern the simultaneous rotation of the CH3 and/or NH3 group, π-flips and free rotations of the organic cation, are used to fit the elastic incoherent structure factor. The 1H NMR spin–lattice relaxation time for all compounds under study, as well as the second moments, has been measured in a wide temperature range. In all studied samples, the temperature dependence of the second moment of the proton NMR line indicated the gradual evolution of the molecular movements from the rigid state up to a highly disordered one.
关键词： quasielastic neutron scattering,phase transitions,perovskite,coordination polymers,dielectric properties,NMR spectroscopy,dynamics,organic cations
更新于2025-11-14 17:28:48
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Effects of repetitive polarization switching on the coercive voltage of Pt/Pb(Zr0.52Ti0.48)O3/Pt thin films analyzed using impedance spectroscopy
摘要： We investigated the effect of repetitive switching of polarization on the ferroelectric Pt/Pb(Zr0.52Ti0.48)O3/Pt thin film capacitor by using impedance spectroscopy. From the Cole-Cole plot, the equivalent circuit is described as a combination of the bulk part (a capacitor), the interface part (the constant phase element (CPE), and a parallelly-connected resistor). The circuit parameters were analyzed at various stages of switching. An early increase and a subsequent decrease of the bulk capacitance may represent the wake-up and fatigue phenomena, respectively. The change in the interface part was characterized by an increase in resistance and the growth of n, the exponent of CPE, which may have come from a reduction of defects and the diminished inhomogeneity in the interfacial layer, respectively. The change in the resistance and the coefficient of the CPE in the interface part collectively resulted in an increase in the interfacial impedance. The coercive voltage, which may have intrinsically increased due to the repetitive switching, was even larger as a result of the increased interfacial impedance.
关键词： Impedance spectroscopy,Wake-up,Coercive voltage,PZT,Fatigue
更新于2025-11-14 17:28:48
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Structural characterization and electrical conductivity analysis of MoO3–SeO2–ZnO semiconducting glass nanocomposites
摘要： A series of glass nanocomposite samples of the general composition formula xMoO3–(1-x) (0.5SeO2–0.5ZnO) for x = 0.05, 0.1, 0.2, and 0.3 have been prepared by solid-state reaction, i.e., slow cooling process. The structural characteristics have been explored by analyzing X-ray di?raction patterns, Fourier-transform infrared, and UV–Vis spectra. The superposition of di?erent nanophases SeO2, SeO3, ZnO, MoO3, Zn (SeO3), Zn (SeO4), Zn (MoO4), Zn2Mo3O8 and ZnMo8O10 over the amorphous glassy matrices have been identi?ed, and their crystallite sizes have been evaluated as well. Fourier transform infrared (FTIR) spectra reveal di?erent types of bonding like Zn–O–Se type and stretching vibrations of MoO6 octahedral units. It is observed that with increasing MoO3 concentration, the estimated values of optical bandgap energy, Urbach energy, and average crystallite size reduce. The dependency of electrical conductivity on frequency and temperature have been analyzed using Almond-West formalism and Jonscher's universal power-law. The non-linear character of DC conductivity and di?erent activation energies at low and high-temperature regions a?rm that the present glassy systems exhibit semiconducting nature. Moreover, DC conduction process is due to small polaron hopping through localized or defect states. The decreasing trend of power-law exponent (s) with temperature rise reveals that AC conduction mechanism is consistent with the correlated barrier-hopping (CBH) model. The existing correlated barrier-hopping model has been modi?ed to attain reasonable values of ?tting parameters and to obtain theoretical values of ideal thermodynamic glass transition temperature. The AC conductivity activation energy and free energy required for small polaron migration reduce with increasing conductivity. The scaling property emphasizes that conductivity relaxation process is subjected to the structure of the composition and does not depend on temperature.
关键词： XRD,UV–vis spectroscopy,Glass nanocomposites,Correlated barrier hopping model,DC and AC conductivity,FTIR
更新于2025-11-14 17:28:48
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Investigating native state fluorescence emission of Immunoglobulin G using polarized Excitation Emission Matrix (pEEM) spectroscopy and PARAFAC
摘要： Intrinsic ?uorescence spectroscopy (IFS) measurements for protein structural analysis can be enhanced by the use of anisotropy resolved multidimensional emission spectroscopy (ARMES). ARMES attempts to overcome the tryptophan (Trp) and tyrosine (Tyr) spectral overlap problem and resolve emitting components by combining anisotropy measurements with chemometric analysis. Here we investigate for the ?rst time the application of polarized excitation-emission matrix (pEEM) measurements and Parallel Factor (PARAFAC) analysis to study IFS from an Immunoglobulin G (IgG) type protein, rabbit IgG (rIgG), in its native state. Protein IFS is a non-trilinear system primarily because of F€orster resonance energy transfer (FRET). Non-trilinearity is also caused by inner ?lter effects, and Rayleigh/Raman scattering, both of which can be corrected by data pre-processing. However, IFS FRET cannot be corrected for, and thus here we carefully evaluated the impact of various different data pre-processing methods on IFS data which used for PARAFAC. Care must be taken with data pre-processing and interpolation, as both had an impact on PARAFAC modelling and the recovered anisotropy values, with residual shot noise from the Rayleigh scatter which overlapped the emission blue edge being the root cause. pEEM spectra from thawed rIgG solutions (15–35 (cid:1)C temperature range) were collected with an expectation being that this temperature range should cause suf?cient emission variation to facilitate component resolution but without major structural changes. However, the only signi?cant changes observed were of the overall intensity due to thermal motion induced quenching and this was con?rmed by the PARAFAC scores. PARAFAC resolved one major component (>99%) for the emission data (polarized and unpolarized) which mostly represented the large Tyr-to-Trp hetero-FRET process, with a second, very weak component (<1%) apparently a contribution from directly excited Trp emission. PARAFAC scores recovered from normalized pEEM data showed minimal change which was further proof for negligible structural change. The results of this study serves as the starting point for the use of PARAFAC analysis of IFS from IgG type proteins and important processes such as denaturation and aggregation.
关键词： Multidimensional,Fluorescence,PARAFAC,Anisotropy,Protein,Spectroscopy,Immunoglobulin G
更新于2025-11-14 15:32:45
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Correlation of acetylene plasma discharge environment and the optical and electronic properties of the hydrogenated amorphous carbon films
摘要： Thin films from polymeric and graphitic hydrogenated amorphous carbon (a-C:H) were deposited over a glass substrate from acetylene (C2H2) plasma by using a conventional plasma enhanced chemical vapor deposition (PECVD). Radio frequency capacitively coupled plasma (RF CCP) source operating at a frequency of 13.56 MHz was used for generation of the discharge. Optical emission spectroscopy (OES) results showed strong optical emissions from diacetylene ion C4H2+ at a wavelength of 506 nm. The energy dispersive X-Ray (EDS) measurements illustrated that the carbon content in the deposited films increased with increasing of power. The Raman and IR results demonstrated that the films deposited at low bias voltages 340 V are so called polymeric a-C:H with high sp3 fraction and high hydrogen content, while the films deposited at high bias voltages 877 V are so called graphitic a-C:H with low sp3 fraction and low hydrogen content. Quantitative information were obtained from fitting the high asymmetrical vibrational modes of Raman and IR spectra by using Fano model expression together with Lorentzian function. The results presented here point out that there is a relation between the intensity of C4H2+ ion emissions and the deposited films properties.
关键词： Optical Emission,diacetylene ion,RF CCP,Hydrogenated amorphous carbon,FTIR,Raman spectroscopy
更新于2025-11-14 15:30:11