Nickel Oxide Films Research Articles

Nickel oxide films with the zinc blende-type structure – A re-evaluation of X-ray diffraction data

The previously unobserved formation of zinc blende-type structured nickel oxide films (NiO1.2) was discovered by the re-evaluation of X-ray powder diffraction data. Nickel oxide films were synthesized by deposition of nickel together with activated oxygen at substrate temperatures of 83K and 298K. At 83K, amorphous NiO films are formed, which crystallize at around 473K forming the rock salt-type structure. In contrast, films deposited at 298K are polycrystalline and form the zinc blende-type structure. Both structures have largely identical lattice parameters with the same nickel fcc sublattice, but with either tetrahedral or octahedral sites filled with oxygen atoms. The only difference observed between the X-ray powder patterns is the intensity of the reflections. The calculation of X-ray difference maps was decisive in distinguishing between the two structures. The Ni-O distances in the zinc blende structure are 181pm, confirming the presence of NiIII in the NiO1.2 film.

Post-growth annealing effect of Li-doped NiO thin films grown by mist chemical vapor deposition

Nickel oxide (NiO) thin films were grown by mist chemical vapor deposition (mist CVD) with various amounts of Li dopant in the precursor (0–15 %). As the Li dopant readily decomposed under the high temperature above 700℃, the post-growth annealing was conducted at 600–800 °C. The crystal quality of the undoped and Li-doped NiO films was improved by thermal annealing due to the crystal reconstruction. The optical transmittance of NiO films was decreased with increasing the amounts of Li dopants, whereas it was increased with thermal annealing. The bandgap of the NiO films was slightly red-shifted with increased amounts of Li dopants, whereas it was blue-shifted with increasing annealing temperature. The resistivity of as-grown NiO films ranged from 25–75 Ω·cm with Li doping. Electrical properties abruptly decreased under a high annealing temperature of 700 °C. Hence, an appropriate combination of Li doping and post-growth annealing might improve the structural properties of the NiO thin films while retaining the p-type conductivity.

Surface Property Regulation of a Magnetron-Sputtered NiOx Hole Transport Layer for High-Performance Inverted Perovskite Solar Cells.

The inverted perovskite solar cells (PSCs) are gaining increasing attention recently for their unprecedented advantages, such as better integration with tandem and flexible designs, negligible hysteresis, good operational stability, and compatibility with commercially scalable fabrication approaches. Nickel oxide (NiOx) films prepared by magnetron sputtering technology exhibit excellent scalability and reproducibility, which could well meet the requirements of the large-scale production of inverted PSCs. However, NiOx prepared by vacuum methods generally has fewer surface hydroxyl groups, deteriorating the wettability and damaging the interface contact with the perovskite. Particularly, the Ni3+ defects on the NiOx surface could lead to unfavorable redox reactions with organic cations in the perovskite under high temperatures, promoting the rapid degradation of the perovskite. Thus, surface regulation of sputtered NiOx is imperative for high-performance PSCs. Herein, 4-(trifluoromethyl) phenylcarbamate hydrochloride (TFFA) was used to regulate the surface properties of sputtered NiOx. The strongly electronegative F ions in TFFA passivated the Ni3+ defects on the NiOx surface, suppressed unfavorable interface reactions, and improved charge recombination. The polar ammonium functional group was used to adjust the surface energy of NiOx, thereby improving the wettability and optimizing the crystallization kinetics of the perovskite. As a result, the power conversion efficiency (PCE) of PSCs reached 22.76%, which was among the highest PCEs reported for sputtered NiOx-based inverted PSCs to date. Moreover, the unencapsulated target devices exhibited better stability, maintaining over 85% of the initial PCE after aging for approximately 1200 h in a N2 environment. Our achievements pointed out a practical strategy for enhancing the performance of sputtered NiOx-based inverted PSCs, which could potentially accelerate the development and application of large-area PSCs.

Using femtosecond laser pulses to investigate the thickness-dependent nonlinear optical properties of nickel oxide thin films and their potential use as optical limiters

In this study, the Z-scan technique was used to investigate the nonlinear optical properties of nickel oxide (NiO) thin films of various thicknesses. Direct current (DC) sputtering was used to deposit single-phase NiO thin films with thicknesses of 280, 350, and 470 nm onto a soda-lime glass substrate. The film structure was measured using X-ray diffraction (XRD) and scanning electron microscopy (SEM), while the linear optical properties were measured using a UV-Vis spectrophotometer. NiO thin films were irradiated with 100 fs laser pulses at various excitation wavelengths and excitation powers to determine the nonlinear absorption coefficient and nonlinear refractive index. The NiO films were found to have reverse saturable absorption and self-focusing behavior. As the thickness of the NiO film increases, both the nonlinear absorption coefficient and nonlinear refractive index decrease. Additionally, the investigation of the optical limitations of NiO thin films revealed a definite association with the thickness of the NiO thin film.

Investigation of diodic behavior in p-NiO/n-SnO2 bilayer heterojunctions fabricated via DC magnetron reactive sputtering

Tin oxide (SnOx) thin films at varying oxygen flow rates and Nickel oxide (NiO) thin films were deposited by reactive dc magnetron sputtering on glass substrates. Structural, chemical, morphological, optical and electrical properties of the deposited films were studied. XRD studies confirmed that the deposited films were polycrystalline in nature. SnOx thin films have shown two phases such as SnO and SnO2. AFM and SEM were used to analyse the morphology of the films and EDS confirmed the presence of Sn and Ni in the respective films. The examination of the x-ray photoelectron spectrum showed that the sputtered SnOx films contain both Sn2+ and Sn4+ oxidation states and NiO films contain Ni+2 and Ni+3 oxidation states. Photoluminescence study shows strong violet and weak red emission peaks for SnOx films and NiO showed strong emission peaks in the orange-red region. The optical results demonstrate that the films were transparent. The bandgap of SnOx and NiO samples were ∼3.3 eV and − 3.42 eV, respectively. Further we constructed a p-NiO/n-SnO2 heterojunction diode and its electrical characteristics were thoroughly assessed. Using dark current–voltage measurements, electrical characteristics such saturation current, ideality factor and barrier height were determined. The increase in oxygen flow rate led to reduction in the rectification of the devices. Our findings support the creation of high-performance metal oxide heterojunction for optoelectronic devices.

Flexible LaNiO3 film with both high electrical conductivity and mechanical robustness

Lanthanum nickel oxide (LaNiO3, LNO) films exhibit excellent electrical conductivity but poor mechanical properties, considerably limiting their further development in the field of flexible electronics. In this study, flexible LNO thin films of different thicknesses were fabricated on a unique two-dimensional (2D) mica platform using a simple metal organic deposition technique. The obtained LNO films exhibited a pseudocubic phase without impurities. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) characterisations proved that the films were well-crystallised, dense, and flat, with controllable thickness. In addition, the flexible LNO/mica element possesses low resistivity (5 × 10−4 Ω cm), translucency, and good bending resistance. The electrical resistivity can remain stable under various bending radii (r = 10∼2 mm), thousands of bending cycles, and a wide temperature range (28–200 °C), demonstrating good durability, mechanical stability and temperature resistance. Furthermore, a ferroelectric BiFeO3 film was constructed based on the obtained conductive LNO electrode, which exhibited typical ferroelectric characteristics. This excellent performance suggests that the flexible LNO electrode is promising for flexible electronic applications.

Preparation of tunable magnesium atom-doped nickel oxide films with short response time and high coloring efficiency by sol-gel method

Nickel oxide, a representative electrochromic material, is commonly employed in environmentally conscious optoelectronic devices, such as multifunctional smart windows. In this paper, novel electrochromic nickel oxide films doped with magnesium atoms were prepared on indium tin oxide (ITO) substrates by sol-gel spin-coating method, and the results of X-ray diffraction and scanning electron microscopy show that the spin-coating is unique in that the existence of a small number of cracks on the surface of the sample is conducive to the enhancement of the electrochemical properties. UV–visible spectrophotometer and electrochemical workstation were used to explore the effect of Mg-atom doping concentration on the electrochromic performance of the nickel oxide thin films, and the results showed that at an annealing temperature of 400 °C, the optical modulation amplitude of the samples with a doping concentration of 4 % reached 43.12 %, and the coloring time and the fading time were reduced to 4.0 s and 3.1 s, respectively, with an increase in the coloring efficiency to 42.25 cm2C−1. In conclusion, Mg doping has an important reference value for the study of electrochromic performance of NiO thin films, and has good prospects for electrochromic applications.

Influence of H2 on the properties of NiOxHy thin films deposited by reactive direct current magnetron sputtering for electrochromic devices

This study aims to optimize the deposition condition of Nickel hydroxide (NiOxHy) films for electrochromic devices by adjusting the H2 gas concentration during the reactive direct current magnetron sputtering. The influence of H2 content on the crystallinity, chemical composition, optical properties, and electrochromic behavior of the NiOxHy films was thoroughly investigated. In the absence of H2 gas in the sputtering system, the Nickel oxide (NiOx) film was obtained as confirmed by the X-ray diffraction results. However, introducing the H2 gas resulted in the formation of NiOxHy film, accompanied by a decrease in the film crystallinity. Fourier transform Infrared spectra were employed to confirm the presence of hydroxyl groups in the as-deposited NiOxHy films. X-ray photoelectron spectroscopy was employed to examine the influence of H2 content on the optical properties of the NiOxHy film. Additionally, it offered valuable insights into the film's chemical composition during the transition from a dark to a transparent state. Our findings revealed that increasing the H2 gas content enhanced the transmittance of NiOxHy films. Here, the optimal H2 flow ratio of 50 % was found to yield a high transmittance of 77.43 % (T550) along with the highest charge density, an optical density changed value of 0.84, and a coloration efficiency value of 83.67 cm2/C. These findings clearly illustrate the substantial influence of H2 concentration on the properties of NiOxHy films, particularly in relation to their application in electrochromic devices.

Atomic Layer Deposited Al1−xNixO: Low Contact Resistivity Hole‐Selective Contact for Crystalline Silicon Solar Cells

Transition metal oxide (TMO)/crystalline silicon (c‐Si) junction‐based heterostructure crystalline silicon solar cells have emerged as a promising alternative to traditional silicon solar cells. However, the power conversion efficiency of c‐Si solar cells utilizing a nickel oxide (NiOx) hole transport layer (HTL) still lags behind those employing a fully developed TMO layer. This disparity may be attributed, at least in part, to inefficient hole extraction. Atomic layer deposited (ALD) aluminum nickel oxide (Al1−xNixO) films, synthesized using bis(N,N′‐di‐t‐butylacetamidinato)nickel(II) (NiAMD) and trimethylaluminum (TMA) as precursors, along with deionized water as a co‐reactant, have been observed to improve the contact properties with p‐type silicon compared to NiOx. Al1−xNixO films with varying Al concentrations (0.25, 0.44, and 0.87) are examined for their contact performance on p‐Si, resulting in the lowest contact resistivity of 85 mΩ cm2. Optimized Al1−xNixO films exhibit superior hole extraction capability from p‐type silicon, leading to a remarkable conversion efficiency of 19.35% in the constructed p‐Si/Al1−xNixO/Ag solar cell. These findings underscore the advantages of utilizing ALD Al1−xNixO as a hole‐selective contact for crystalline p‐Si solar cells.

Synthesis, characterization, and CO sensing properties of NiO thin film for commercial aircraft applications

Abstract The detection of combustion gases such as carbon monoxide (CO) and fuel leaks is a concern in regard to aeronautical safety and has led to the development of semiconductor sensors. The focus of this work is the detection of CO within commercial aircraft using a thin film of nickel oxide (NiO) as the sensing element. The NiO phase was synthesized using the sol-gel method using a modification of the procedures proposed by N. Talebian and B. Pejova. Microstructural characterization of the NiO thin film was performed using scanning electron microscopy (SEM), X-ray diffraction (XRD), and transmission electron microscopy (TEM). Optical analysis was carried out using diffuse reflectance (UV-VIS) spectroscopy. The results showed that the NiO thin film was homogeneous and composed of nodular nanoparticles with size between 10 and 15 nm and thickness of 75 nm. The band gap value was 3.3 eV, which is consistent with p-type semiconductors. The sensitivity of the devices was determined by means of the static environment method. The best operation temperature was 200°C for the device with 100-µm spacing between tracks, which gave a response time of 165 seconds and recovery time of 212 seconds according the results of a flow-through method. The device with this track spacing is ideal for CO detection at 50 ppm, at which the first symptoms of intoxication appear in humans inside commercial aircraft.

Ultra-fast switching of energy efficient electrochromic nickel oxide thin films for smart window applications

In today's modern world, energy consumption continues to escalate. In such cases, smart windows play a crucial role in reducing energy consumption and enhancing the quality of life. Electrochromic devices (ECDs) -based smart windows rely profoundly on nickel oxide (NiO) thin films, which act as a counter electrode in ECDs. This work aims to fabricate NiO thin films, with the intention of achieving ultrafast ECD. Through the sputtering technique, energy-efficient ECD is obtained with the highest optical modulation of 60 % at a rapid switching speed of 0.55s for bleaching and 0.95s for coloration. We have also investigated the structural, morphological, vibrational, and optical properties of NiO thin films. XRD analysis revealed the less crystalline or near amorphous nature of NiO thin film. XPS, PL, and Raman studies confirm the existence of defects in the film. The favourable, less crystalline nature, along with the presence of defects, facilitates ultra-fast ion intercalation and de-intercalation process. We believe that prepared NiO film can be used as a promising anodic colourant in electrochromic smart windows with applications in energy-efficient buildings.

Characterization of the p-NiO/n-GaN heterojunction and development of ultraviolet photodiode

Nickel oxide semiconductor is a good p-type material for fabricating a p-n-heterojunction with n-type GaN semiconductor. The p-NiO/n-GaN heterojunction, which produces a type II band bias, has significant prospects for creating photosensitive devices. Herein, it is shown that a selective ultraviolet photodetector can be created based on this heterojunction. p-NiO films were formed using magnetron sputtering onto n-doped GaN epitaxial layers grown by plasma assisted molecular beam epitaxy. The structural, optical, and electronic properties of the formed nickel oxide films were studied. A mechanism for reducing dislocation density and conductivity and increasing transparency due to film annealing is proposed. It has been established that the current–voltage characteristics of the p-NiO/n-GaN heterojunction are typical for diode structures and show selective sensitivity to ultraviolet radiation. The band model and sensitivity of the fabricated ultraviolet photodiode were evaluated. The photosensitivity at zero voltage was 3.11 mA/W, the quantum yield was 0.011, and the detection ability was 8.69 × 109 Jones. The work shows the potential of using the p-NiO/n-GaN heterojunction to create ultraviolet photodetectors.

Optical properties of NiO films: Effect of nitrogen-doping, substrate temperature and band gap estimation using machine learning

In this study, nickel oxide (NiO) thin films were synthesized on glass substrates using RF magnetron sputtering with varying nitrogen (N) doping ratio and substrate temperatures to explore modifications in their structural, morphological, and optical properties. The films were prepared using a high-purity NiO target under controlled sputtering conditions. Structural analysis by X-ray diffraction revealed an improvement in crystallinity in the (200) direction with increasing N ratio. In contrast, higher N ratio led to the suppression of (111) and (220) peaks, indicating a significant influence of N on the crystal structure and orientation. The films’ thickness and morphology, examined using scanning electron microscopy and energy-dispersive X-ray spectroscopy, showed uniform and homogeneous growth with smooth surface topologies. Optical properties, assessed by UV–Vis-NIR spectrophotometry, demonstrated a decrease in transmittance and a redshift in the absorption edge with increased N doping, corresponding to a narrowing of the energy bandgap from 3.7 eV to 3.45 eV. This bandgap reduction is attributed to N incorporation substituting oxygen sites, introducing defect states within the band structure. Additionally, the impact of substrate temperature on film growth enhanced crystallinity and orientation along the (111) plane at higher temperatures, with a simultaneous reduction in film thickness due to increased adatom mobility and potential thermal decomposition. The evaluation of Kernel Ridge Regression (KRR) and Ridge Regression (RR) models revealed their effectiveness in predicting band gap values for thin films at varying substrate temperatures and thicknesses. While RR excelled in predicting a band gap of 3.6 eV for a film with a substrate temperature of 24 °C and a thickness of 112.7 nm, KRR outperformed in predicting a band gap of 3.65 eV for a film with a substrate temperature of 24 °C and a thickness of 107 nm. These findings elucidate the dual influence of N doping and substrate temperature on enhancing the functional properties of NiO thin films, promising for applications in optoelectronic devices and gas sensors.

Studies of carrier transport mechanism in NiO/Ag/NiO transparent conducting electrode/ZnO metal-semiconductor-metal photodetectors

Oxide/metal/oxide multilayers as a transparent conducting electrode (TCE) have been developed to replace metals due to their high transparency and low sheet resistance. Nickel oxide (NiO) film with a high work function was used as an oxide to form NiO/Ag/NiO (NAN) TCE, therefore a high barrier height between NAN/zinc oxide (ZnO) interface. In the study, NAN TCE was deposited on ZnO surface to fabricate metal-semiconductor-metal (MSM) photodetectors (PDs) and study its carrier transport mechanism. The NAN TCE has a low sheet resistance of 6.5 Ω/sq. and transmittance more than 40% in a 300−1000 nm wavelength range. Such issues result in the figure-of-merit is higher (2.3 × 10−4 Ω−1) than that (2.5 × 10−7 Ω−1) of pure single NiO thin film. As compared to the conventional Au/ZnO MSM-PDs, the NAN/ZnO MSM-PDs demonstrates a lower leakage current as a result of Ni atoms diffusing into ZnO and passivating the defects. Due to the high work function of NiO, the NAN/ZnO interface exhibits a barrier height as high as 0.91 eV. The Au/ZnO MSM-PDs reveals only one carrier conduction of ohmic due to the electrons tunnel form Au into ZnO through the surface defects. In contrast, two distinct carrier transport mechanisms were observed in the NAN/ZnO MSM-PDs. At low-voltage for V⩽0.64 V , ohmic conduction dominates and the electrons inject from NAN to ZnO, trapped by the defect states of ZnO. At high-voltage for V⩾0.64 V , the trapped electrons acquire enough energy and emit from trap to conduction band, entering Poole–Frankel emission transport.

Effect of annealing temperature on physical properties and photoelectrochemical behavior of electrodeposited nanostructured NiO thin films for optoelectronic applications

Our paper used a low-cost electrodeposition technique to grow Nickel Oxide (NiO) thin films on fluorine-doped tin oxide (FTO) substrate. As-deposited films were annealed at different temperatures (350, 400, 450, and 500 °C). X-ray diffraction (XRD), Raman spectroscopy (RAM), scanning electron microscopy (SEM), UV–vis spectrophotometer, photoluminescence (PL), Cyclic voltammetry (CV), photocurrent (PC), electrochemical impedance spectroscopy (EIS), and Mott-Schottky analysis (MS) were used to study and investigate the effect of annealing temperatures on the structural, morphological, electrical, and optical properties of prepared thin films. XRD patterns proved the cubic phase of all NiO samples with the preferential orientation in (111) direction. SEM results showed that the grain size increased with increasing annealing temperature. The optical transmission was studied by a UV–vis spectrophotometer, where high transmittance for NiO thin films was found to vary in the range of 73–84 % in the visible wavelength region, depending on the annealing temperatures. At the same time, UV–visible measurements indicate an absorption band edge at 311 nm, mainly recognized as a characteristic direct band gap for prepared NiO. The optical gap calculated from the Tauc relation showed a decreasing trend from 3.97 to 3.86 eV with increasing annealing temperature from 300 °C to 500 °C. PL spectra of synthesized samples revealed two distinct emission peaks at around 400 nm and 490 nm. RAM analysis confirmed the presence of three characteristic peaks related to the vibration of Ni–O bonds. The NiO film annealed at 500 °C displays the highest specific capacitance value by CV analysis. The P-type conductivity of manufactured arrays and enhanced electrical properties were confirmed by PC, EIS, and MS analysis. The highest carrier concentration values (9.19 × 1018 cm−3) and flat band potential (0.82 V) were obtained for samples annealed at 500 °C. Our outcomes proved that NiO-500 °C thin films are ideal candidates for optoelectronic applications.

Analysis of effect of annealing at high temperature on nickel oxide and zinc oxide thin film for solar cell applications

The use of thin films in solar cell technology has gained substantial interest because of their potential for cost-effective and efficient energy conversion. nickel oxide (NiO) and zinc oxide (ZnO) have been used as potential materials in solar cells application especially third generation solar cells because of their good characteristics, such as high electrical conductivity, chemical stability, resistance to degradation, and abundance and low cost. However, at high temperatures, both NiO and ZnO can undergo thermal decomposition and exhibit crystal defects and grain boundaries. This work investigates high temperature annealing on the morphology, structural, and optical properties of NiO and ZnO thin films. The deposited material was annealed at 500 ℃, 600 ℃, and 700 ℃ and be characterized via scanning electron microscopy (SEM), XRD, and UV-Vi’s spectroscopy. The results showed that inceasing the annealing temperature can improve both ZnO and NiO thin films in structure and appearance. For ZnO, higher temperatures made the grains bigger and more orderly, and for NiO, the process made the grains more organized, bigger in size, and spread out more evenly. However, annealing at high temperature yields a smaller bandgap energy value for both thin films.

Evaporated Nickel Oxide Films with Slow Annealing and Interface Modification for Perovskite Solar Cells.

Electron-beam-evaporated nickel oxide (NiOx) films are known for their high quality, precise control, and suitability for complex structures in perovskite (PVK) solar cells (PSCs). However, untreated NiOx films have inherent challenges, such as surface defects, relatively low intrinsic conductivity, and shallow valence band maximum, which seriously restrict the efficiency and stability of the devices. To address these challenges, we employ a dual coordination optimization strategy. The strategy includes low heating rate annealing of NiOx films and using an aminoguanidine nitrate spin coating process on the surfaces of NiOx films to strategically modify NiOx films itself and the interface of NiOx/PVK. Under the synergistic effect of this dual optimization method, the quality of the films is significantly improved and its p-type characteristics are enhanced. At the same time, the interface defects and energy level alignment of the films are effectively improved, and the charge extraction ability at the interface is improved. The combined treatment significantly improved the efficiency of inverted PSCs, from 17.85% to 20.31%, and enhanced device stability under various conditions. This innovative dual-coordinated optimization strategy provides a clear and effective framework for improving the performance of NiOx films and inverted PSCs.

NiO thickness measurement using a rectangular-type Sagnac interferometer as the material transport layer in a perovskite solar cell

This work aims to utilize a phase-shifting technique in a rectangular-type Sagnac interferometer (RTSI) to measure the thickness of a thin film of nickel (II) oxide (NiO) in an electron transport layer (ETL) in perovskite solar cell preparation. The NiO layer is deposited on a fluorine-doped tin oxide (FTO) glass substrate. In the RTSI setup, the signal output from the interferometer is divided into the reference and testing arms using a nonpolarizing beam splitter (NPBS). The balanced photodetectors then detect the signal, with the FTO/NiO layer placed in the testing arm and pure FTO in the reference arm. By analyzing the signal intensities at polarization settings of 0° to 180°, the phase shift and thickness of the NiO layer can be determined. The thickness values of FTO and NiO films obtained through three different phase-shifting algorithms of three-, four-, and five-steps are calculated. The obtained NiO thickness values are validated against scanning electron microscopy (SEM). Finally, by considering the NiO thickness value that exhibits the lowest percentage error compared to one from SEM, it is confirmed that the three-step algorithm is the most suitable scheme for obtaining intensities at 0°, 45°, and 90°. Therefore, the proposed setup shows promise as a replacement for SEM in thickness measurements.

Electro-optical properties of solution-processed aluminum–nickel oxide film containing graphene oxide in liquid crystal system

Electro-optical properties of solution-processed aluminum–nickel oxide film containing graphene oxide in liquid crystal system

Room-temperature processed plasma activated nickel oxide film for wide-bandgap perovskite solar cells

The nickel oxide (NiOx) film is often employed as a hole transport layer for the production of high-performance inverted perovskite solar cells due to its exceptional chemical stability, high hole mobility, and matching energy level structure. Among various techniques for preparing NiOx, E-beam evaporation-based NiOx films show great promise owing to their low fabrication temperature and excellent photoelectric properties. Herein, an ion bombardment source was used to generate oxygen plasma through the bombardment of oxygen molecules, which subsequently oxidized the non-stoichiometric NiOx. Experimental findings demonstrate that this method substantially enhances the electrical and optical properties of the NiOx film. We utilized a room-temperature-processed NiOx film as a hole transport layer to fabricate inverted wide-bandgap perovskite solar cells, resulting in a champion device efficiency of 17.82%. It is anticipated that the NiOx films produced via this approach will be widely adopted in the industrialization of perovskite solar cells.