Molybdenum Oxide Thin Films Research Articles

Effect of annealing on MoOx and interface properties for carrier-selective contact solar cells with different passivation layers

The structural, electrical and optical properties of molybdenum oxide (MoOx) thin films prepared by magnetron sputtering are studied with annealing temperature. The interface properties of silicon with the intrinsic amorphous silicon (a-Si:H(i)) and alumina (AlOx) passivation layers are investigated by the minority carrier lifetime and implied-Voc (iVoc). The AlOx shows the better passivation properties and thermal stability for the carrier-selective contact solar cells. The Ce-doped In2O3(ICO) is deposited on the surface of MoOx thin films. It is found that the optimized annealing temperature is 125 °C for the carrier selective contact solar cells with the a-Si:H(i) passivation layer. It could increase to 175 °C for the AlOx passivation layer.

Efficient hole transport layers for silicon heterojunction solar cells by surface plasmonic modification in MoOx/Au NPs/MoOx stacks

This study explores the integration of Au nanoparticles (NPs) into molybdenum oxide (MoOx) thin films to form a MoOx/Au NPs/MoOx (MAM) stack. This stack serves as a hole transport layer (HTL) in silicon heterojunction solar cells, aiming to address the challenges of safety concerns and inefficient carrier transport. Ultraviolet photoelectron spectroscopy and X-ray photoelectron spectroscopy spectra demonstrate that the incorporation of Au NPs notably raises the work function of MAM to 5.85 eV and stabilize Mo6+ concentrations at 94.07%. In addition, Au NPs effectively act as a shield against detrimental interactions with Ag, thereby improving the interfacial stability between the back electrode and HTL. This strategic enhancement facilitates the formation of surface plasmon polaritons, reduces the contact resistance to 41.19 mΩ cm2, and boosts the quantum efficiency by injecting hot electrons and intensifying the surface electric field. These advancements lead to a significant enhancement in the fill factor and short-circuit current, leading to the development of a heterojunction solar cell with an increased efficiency (Eff) from 19.81% to 22.03%. This investigation underscores the transformative potential of engineered nanomaterials in elevating the performance and stability of photovoltaic devices, promoting the wider adoption of renewable energy technologies.

Study on structural, optical, and electrical properties of yttrium doped molybdenum oxide thin film and its MIS diode performance

In this study, Orthorhombic pure MoO3 and various weight percentages of Y-doped MoO3 nanostructure arrays were successfully deposited using the simple jet nebulizer spray pyrolysis process at an ideal substrate temperature of 500 °C. In order to create metal-insulator-semiconductor-based Schottky barrier diodes, Y-doped MoO3 nanostructure arrays were employed as an insulating layer. The influence of Y-doped MoO3 concentration during the deposition process was carefully analyzed in relation to the structural, morphological, optical, and electrical characteristics of Y-doped MoO3 nanostructure array films. The produced films' crystalline nature with an orthorhombic phase was shown by the XRD pattern. An FE-SEM was used to analyse the solidly linked plate-like structure of Y-doped MoO3 at higher concentrations of 6 wt%. The EDAX spectrum was used to confirm the stoichiometric relationship between the elements O, Mo, and Y. The band gap values of the Y-doped MoO3 were determined using UV–Vis spectroscopy to range from 3.3 to 3.18 eV with doped concentrations. The film made with 6 wt% Y doped MoO3 showed a sharp improvement in electrical conductivity according to a DC electrical analysis. Notably, MIS diode made with 6 wt% Y-doped MoO3 in particular showed a low ideality factor (n = 2.63), strong photosensitivity (PS = 17,509.62%), responsivity of 738 mA/W, and a maximum QE of 97.49% under illumination (130 mW/cm2). Additionally, a 6 wt percent Y-based diode obtained a greater detectivity of D* = 7.16 1009 jones in a dark environment condition.

Interface study of molybdenum oxide thin films on n- and p-type crystalline silicon surface

Interface study of molybdenum oxide thin films on n- and p-type crystalline silicon surface

The effect of substrate temperature on the preparation of molybdenum oxide thin films by spray pyrolysis method used in diode

The effect of substrate temperature on the preparation of molybdenum oxide thin films by spray pyrolysis method used in diode

Conductance modification of molybdenum oxide thin films through oxygen-vacancy engineering for visible-blind ultraviolet photodetection

We propose a simple approach to locally modify the conductance of molybdenum oxide thin films with thermal annealing in oxygen atmosphere at relatively low temperature for constructing a visible-blind ultraviolet photoconductor. The amorphous MoO x is grown by remote plasma enhanced atomic layer deposition (RPALD), and then crystallized into α-MoO x at 500 °C in argon atmosphere, which exhibits good conductance with resistivity of 3.9 × 10−3 Ω cm due to the formation of oxygen vacancies. Good ohmic contact between Ti and the crystallized MoO x is demonstrated with specific contact resistance of 9.74 × 10−4 Ω cm2. The lateral Au/Ti-MoO x -Ti/Au structures are defined and the conductance of the exposed MoO x channel is significantly modified by thermal annealing in oxygen atmosphere to form a photodetector, which shows obvious photoresponse at the wavelength of less than 372 nm with low dark current of 0.9 pA at 5 V, and the remarkable responsivity of 0.75 mA W−1 at 280 nm is achieved with a high ultravoilet/visible rejection ratio. The low dark current and incredible responsivity can be attributed to the good ohmic contacts of untreated MoO x and the reduction of number of oxygen vacancies in the MoO x channel. The key role of oxygen vacancy on the conductance of MoO x has been demonstrated. Those results suggest that the MoO x thin films are promising candidate for visible-blind ultraviolet photodetectors in a simple complementary metal oxide semiconductor (CMOS)-compatible process.

Nanostructured solar cells based on MoO3 film deposition

Electrodeposited molybdenum oxide thin films are used as a buffer layer between the indium tin oxide (ITO) anode and the organic electron acceptor film in organic solar cells. The MoO3 films are deposited at room temperature using a solution of molybdic, acid and citric acid as complexing agents. Such electrodeposited MoO3 ultra thin films (10-20 nm) has been used as buffer layer (BF) in ITO/BF/copper phthalocyanine (CuPc)/fullerene (C60)/ aluminium tri (8-hydroxyquinoline) (Alq3)/ aluminium photovoltaic cells. It is shown that this electrodeposited MoO3 buffer layer enhances the charge transfer from CuPc to ITO through a decrease of the effective barrier, present at the interface CuPc/ITO. This improving effect is directly highlighted by the shape of the J-V curves. The kink effect, due to the barrier present at the interface ITO/organic, disappears when the electrodeposited molybdenum oxide buffer layer, is introduced at this interface, which testifies of the decrease of the barrier.

Impact of annealing on charge storage capability of thermally evaporated molybdenum oxide thin films

Rapid technological advancements in recent years have necessitated the creation of energy-related devices. Due to their unique properties, including an exceptional cycling life, safe operation, low processing cost, and a higher power density than batteries, supercapacitors (SCs) have been identified as one of the most promising candidates to meet the demands of human sustainability. To increase the energy density of SCs, several advanced electrode materials and cell designs have been researched during the past few years. Utilizing the Faradaic charge storage process of transition metal cations, transition metal compounds have recently received attention as prospective electrode materials for SCs with high energy densities. In this work, the structure, morphology and electrochemical properties of molybdenum oxide (MoO3) films deposited via thermal evaporation technique and annealed at various temperatures were systematically investigated in order to examine the potential use of MoO3 for supercapacitors. Electrochemical analysis confirmed the pseudocapacitance characteristics of the synthesized films. The annealing temperature affects the oxidation and reduction observed in the cyclic voltammetry (CV) plots. Areal capacitance of thin films annealed at 150°C was found to be maximum and this could be attributed to the formation of hollow tube-like nanostructures which provided more active sites, than films annealed at higher temperatures. This also influences the charge storage ability of the synthesized films. It would be logical to assume that additional research in this area will result in more interesting discoveries and, eventually, the vi-ability of those promising Mo-based compounds in high-tech energy storage systems.

Numerical and Experimental Investigations of the Photothermal Effect in Thin Films of Molybdenum Oxide under Laser Ablation

Numerical and Experimental Investigations of the Photothermal Effect in Thin Films of Molybdenum Oxide under Laser Ablation

Photocatalytic properties of molybdenum oxide photoelectrode synthesized by spray pyrolysis method

The present work reports the photoelectrocatalytic properties of pyrolyzed molybdenum oxide thin film. Microstructural analysis revealed clustered nanoaggregates. Structural analysis showed a polycrystalline $$\alpha$$ -MoO3 phase. The crystallite size, dislocation density, microstrain, and stacking faults were found to be 41.27 nm, 5.87 × 10−4 lines/cm2, 8.41 × 10−4 and 1.78, respectively. The optical bandgap was found to be 3.20 eV. Linear sweep voltammetry measurement in 1 M KOH electrolyte revealed a significant photocurrent density of 992.39 μA/cm2 at a bias of 1.2 V versus Ag/AgCl (1.4 V vs. RHE). The reasonable performance of the device suggests that the rarely deployed spray pyrolysis method is promising for preparing photoactive $$\alpha$$ -MoO3 films for photoelectrochemical measurement.

Atomic layer deposition of MoOx thin films using Mo(iPrCp)2H2 and O3

This work studied the growth of molybdenum oxide thin films with thermal atomic layer deposition (ALD) using Mo(iPrCp)2H2 and O3 as precursors. Growth parameters were determined by varying growth temperature and precursor dose times. ALD growth was exhibited in a temperature range of 100–200 °C. The growth per cycle ranged from 1.3 to 1.7 Å/cycle with a standard uniformity parameter of <5%. Attempts to grow films using H2O as an oxygen source showed no significant growth. Film properties were measured using spectroscopic ellipsometry, x-ray reflectivity, x-ray diffraction, x-ray photoelectron spectroscopy, and infrared spectroscopy.

Achievement of high infrared photoresponse in n-MoO3/p-Si heterostructure photodiode prepared via the thermal oxidation method, the influence of oxygen flow rate

For the first time, the molybdenum oxide (MoO3) thin films were deposited on a p-type Si substrate to create a heterojunction infrared (IR) photodiode via the simple thermal oxidation technique, while the oxygen flow rate was varied from 20 to 80 sccm. The XRD diffractograms confirmed the formation of an orthorhombic structure (α-MoO3 phase) in all the synthesized layers, consistent with their Raman spectra. The FESEM images showed that the prepared samples have similar flat flakes on top and nano-spherical particles underneath with a thickness of 220 ± 20 nm. The current density-voltage (J-V) measurements showed that with increasing O2 flow rate, the overall rectification ratio (IF/IR) of the samples is increased, with a maximum of 43.60 for the one fabricated at 60 sccm O2 flow rate. Also compared to other layers, this sample with the highest oxygen vacancies, i.e., MoO2.84, showed this property led this sample to achieve the highest photoresponse ratio (ILight/IDark) of 17 to the 835 nm IR radiation.

Plasma-Enhanced Atomic Layer Deposition of Molybdenum Oxide Thin Films at Low Temperatures for Hydrogen Gas Sensing.

Molybdenum oxide thin films are very appealing for gas sensing applications due to their tunable material characteristics. Particularly, the growing demand for developing hydrogen sensors has triggered the exploration of functional materials such as molybdenum oxides (MoOx). Strategies to enhance the performance of MoOx-based gas sensors include nanostructured growth accompanied by precise control of composition and crystallinity. These features can be delivered by using atomic layer deposition (ALD) processing of thin films, where precursor chemistry plays an important role. Herein, we report a new plasma-enhanced ALD process for molybdenum oxide employing the molybdenum precursor [Mo(NtBu)2(tBu2DAD)] (DAD = diazadienyl) and oxygen plasma. Analysis of the film thickness reveals typical ALD characteristics such as linearity and surface saturation with a growth rate of 0.75 Å/cycle in a broad temperature window between 100 and 240 °C. While the films are amorphous at 100 °C, crystalline β-MoO3 is obtained at 240 °C. Compositional analysis reveals nearly stoichiometric and pure MoO3 films with oxygen vacancies present at the surface. Subsequently, hydrogen gas sensitivity of the molybdenum oxide thin films is demonstrated in a laboratory-scale chemiresistive hydrogen sensor setup at an operation temperature of 120 °C. Sensitivities of up to 18% are achieved for the film deposited at 240 °C, showing a strong correlation between crystallinity, oxygen vacancies at the surface, and hydrogen gas sensitivity.

Multitarget Reactive Magnetron Sputtering towards the Production of Strontium Molybdate Thin Films

X-ray photoelectron spectroscopy was used to study the direct synthesis of strontium and molybdenum oxide thin films deposited by multitarget reactive magnetron sputtering (MT-RMS). Sr and Mo targets with a purity of 99.9% and 99.5%, respectively, were co-sputtered in an argon-oxygen gas mixture. The chamber was provided with an oxygen background flow plus an additional controlled oxygen supply to each of the targets. We demonstrate that variation in the power applied to the Mo target during MT-RMS enables the production of strontium and molybdenum oxide films with variable concentrations of Mo atoms. Both molybdenum and strontium were found in the oxidized state, and no metallic peaks were detected. The deconvoluted high-resolution XPS spectra of molybdenum revealed the presence of several Mo 3d peaks, which indicates molybdenum bonds in a lower valence state. Contrary to the Mo spectra, the high-resolution strontium Sr 3d spectra for the same samples were very similar, and no additional peaks were detected.

Pseudostoichiometric and oxygen deficient MoOx for efficient sensing of H2S and CO at relatively low operating temperature and analyte concentrations

Pseudostoichiometric molybdenum oxide (MoOx) thin films were deposited on glass substrates using radio frequency magnetron sputtering from sintered molybdenum trioxide (MoO3) target at relatively low substrate temperature in inert (Ar) atmosphere. Structural, morphological, and electrical properties of the deposited films were studied thoroughly, followed by detailed investigations on the sensing performance of the same toward two hazardous and toxic gases, hydrogen sulfide (H2S) and carbon monoxide (CO); specifically at low operating temperature and with low concentrations. Good response percentages with satisfactory response and recovery time were obtained for both the gases. These might be attributed to the presence of oxygen deficient and well distributed nanostructures on the surface of the film that facilitate gas adsorption/anchoring and promotes the charge transfer reactions on the surface of the semiconductor. Furthermore, extensive sensing measurements and post-sensing structural characterization were carried out, which revealed long-term stability of the sensing platform.

Plasma-enhanced atomic layer deposition of molybdenum oxides using molybdenum hexacarbonyl as the precursor

Molybdenum oxide (MoOx) thin films are fabricated by plasma-enhanced atomic layer deposition (PEALD) using molybdenum hexacarbonyl Mo(CO)6 as the precursor and oxygen as the reactant. The effect of plasma power for oxygen has been investigated on the evolution of film structure. Molybdenum oxide shows the orthorhombic α-MoO3 phase at low powers and gradually changes to the metastable monoclinic β-MoO3 phase as the power continually increases, which is confirmed by Raman spectroscopy. α-MoO3 is two-dimensional (2-D) phase with Pbnm space group, while β-MoO3 film belongs to three-dimensional phase with P21/c. From the observation of scanning electron microscopy (SEM), a rod-like structure has been detected, whereas a bulk-like grain corresponds to a high ratio of β-MoO3 to α-MoO3 phase at higher power of 150 W. Due to better coverage of 2-D layer preventing surface from oxidation, the interfacial layer of α-MoO3 checked from transmission electron microscopy (TEM) shows thinner at low powers when contacting with silicon substrate, which is consistent with the performance of leakage current. The changes in binding energies of Mo 3d and O 1s orbits at different milling depths are compared by different powers. Though the significant amount of Mo4+ oxidation state is shown from x-ray photoelectron spectroscopy (XPS), only α-MoO3 and β-MoO3 crystallites with +6 state of Mo are observed from x-ray diffraction (XRD) patterns. Above phenomenon is due to the structural change caused by the loss of oxygen atoms. Thus, according to the charge transformation and compensation, the defect reaction model can well explain that oxygen vacancies inside films are more prevalent in orthorhombic phase at low plasma power for oxygen of our reduced MoO3-x.

Simulation of perovskite solar cells using molybdenum oxide thin films as interfacial layer for enhancing device performance

Organic-inorganic hybrid perovskite solar cells (PSCs) have the issue of interdiffusion at the interfaces that causes undesirable phenomena affecting device efficiency and stability. In this paper, we have investigated MoOx thin films as interlayer between the hole transport material and gold electrode and develop a model using the SCAPS solar cell simulator as a function of the interlayer film thickness to enhance device efficiency and stability. First, different thicknesses (2, 5, 10, 50, and 100 nm) of MoOx films were deposited on glass substrate by electron beam evaporation (e-beam) and their physical, chemical, optical, and electronic properties for PSC were examined. In this research, uniform, homogeneous and pinhole free MoOx films with high transmittance (˃ 80%), very low surface roughness, and resistivity were obtained from the 5 and 10 nm thick samples. In addition, the 10 nm film has shown the lowest photoluminescence emission. Using SCAPS solar cell simulation software and including MoOx thin films as passivation layer, the performance of the PSCs for a Pb-based and Pb-free perovskite absorber were modelled. Results showed that the 10 nm MoOx film is found to provide the best benefit to the device performance with enhanced power conversion efficiency (PCE) of 16.9% and 12.4% for the lead-based MAPb(I1-xBrx)3 and lead-free (MASnI3) perovskite solar cells, respectively.

Visible-Light-Enhanced Electrocatalytic Hydrogen Evolution Using Electrodeposited Molybdenum Oxide

Electrocatalytic hydrogen production using inexpensive catalysts and solar energy has become a critical research direction due to its economic interest and environmental friendliness. Photoresponsive semiconductors play a key role in this field. In this work, we demonstrate visible light-responsive, mixed-valence, molybdenum oxide (MoO3−x, 0 ≤ x ≤ 1) thin films with oxygen vacancies that are electrochemically deposited in a period of seconds through an ammonium heptamolybdate electrolyte. XRD, XPS, SEM, TEM, EPR, Raman, and electrochemical techniques (Linear Sweep Voltammetry, Chronoamperometry, Electrochemical Impedance Spectroscopy, Tafel analysis) have been utilized to characterize the MoO3−x films. Diffuse reflectance spectroscopy (DRS) and the Mott-Schottky (MS) plot reveal that the as-deposited semiconductive MoO3−x film possesses an optical bandgap of ∼2.53 eV and a flat band potential of ∼0.40 eV, respectively. The MoO3−x films exhibit up to 152% electrocatalytic current improvement in the hydrogen evolution reaction (HER) upon illumination with visible light compared to in the dark. The superior electrocatalytic activity of the as-deposited MoO3−x films under illumination is attributed to the lower bandgap, lower overpotential, decreased electronic resistivity, and a smaller Tafel slope. Our experimental exploration suggests that MoO3−x can be potentially applied as an effective, low-cost electrode material for high-performance solar energy-assisted hydrogen fuel production.

Reflections of thin film surface roughness on graphs of specklegram: a novel approach

The advancement in thin-film technology necessitated the development of more reliable, sensitive, and non-destructive methods for the quality analysis of thin films. Graph theory, the mathematical and analytical tool, has gained significant importance in analysing complex signals and images. The paper introduces a novel surrogate method based on graph theory to analyse the specklegrams of thin films for quality analysis. The method is deciphered through the complex network analysis of the electronic specklegrams of the molybdenum oxide thin films sputtered at different Argon pressures. For this, graph features are determined from the graphs constructed using the seven equally spaced columns of the specklegram data of a film. The heat map of the specklegram displays the morphological modifications in the film surface. The study reveals a decrease in the centrality measures and multifractal dimension for the film samples. The decrease of root mean square surface roughness of the films calculated from the atomic force microscopic images suggests its relation with centrality measures indicating the potential of centrality measures of the specklegrams as a surrogate method for thin-film quality analysis.

Impedance spectroscopy and transport mechanism of molybdenum oxide thin films for silicon heterojunction solar cell application

Impedance spectroscopy and transport mechanism of molybdenum oxide thin films for silicon heterojunction solar cell application