Defects In ZnO Research Articles

Synthesis of zinc oxide semiconductor nanoparticles using natural extract: a systematic evaluation of cationic dye photodegradation influenced by extract concentration, catalyst dose, and pH.

This work obtained zinc oxide nanoparticles (ZnO NPs) using organic components extracted from Waltheria americana at different concentrations. ZnO materials were subsequently applied in the photodegradation of two cationic dyes, Rhodamine B (RB) and methylene blue (MB), at different doses of catalyst and pH. The crystallinity and hexagonal Wurtzite structure of ZnO were established through XRD analysis. The Zn-O bond in the ZnO NPs was confirmed in the FTIR, with the characteristic signals observed in the fingerprint region at ~ 400cm-1. SEM and TEM revealed the formation of quasi-spherical particles with an average size ranging from 2 to 12nm, depending on extract concentrations during synthesis. UV-Vis studies indicated the optical bandgap of ZnO, with values below 3eV, also dependent on extract concentration. PL analysis revealed the recombination of free excitons and defects in ZnO. Photocatalytic studies of ZnO materials demonstrated excellent degradation efficiency of RB and MB dyes, which was influenced by the extract concentration of NPs, while the degradation of MB was enhanced with a 1:1 dye-to-catalyst ratio under acidic conditions. In contrast, due to RB more complex structure, an increased ratio of 1:1 to 1:3 and acidic pH conditions improved its degradation. Green-synthesized ZnO NPs using photocatalysis techniques exhibit significant potential as eco-friendly alternatives for removing contaminants from water.

Hierarchical Bi2S3 nanothorn on ZnO core-branch photoelectrode: A promising heterostructure for enhanced photoelectrochemical water splitting

The zinc oxide semiconductor associated with defects and their recombination effect restricts the development of photoelectrode for hydrogen evolution. The combination of semiconductor hetero-junction and hierarchical interface of ZnO/Bi2S3 photoelectrode fabricated. In this study, heterostructure ZnO/Bi2S3 were studied as a photoanode with their impact of oxygen vacancy in ZnO nano rods. The trace of the Bi2S3 on the ZnO was studied and compared with pristine and oxygen annealed ZnO nano rods. The photon-luminescence studies reveal that shallow donor and acceptor defect in ZnO and restricted by Bi2S3 heterostructure. The less defect contemplations in the photoanodes accelerates up electron and hole migration leading to significant built-in potential and photocurrent generation. The appropriate method has been followed to architype less interfacial defect in ZnO(300)/Bi2S3 photoanode and boosted the photo-redox reactions for efficient hydrogen evolution. The photoanode exhibits substantial properties of photocurrent density 0.33 mA/cm2, charge transfer resistance of 700 Ω cm2 and higher inbuilt potential of −0.88V vs Ag/AgCl with 0.17 % applied bias photon to electron conversion efficiency and 0.11 % solar to hydrogen conversion efficiency.

Electron field emission property of NiO-decorated ZnO nanorods grown on diamond films

ZnO/micron diamond (MCD) composite structure combines two wide-band gap semiconductor materials, providing stable performance suitable for high-performance electron field emission (EFE) devices operating in various complex environments. Nonetheless, the optical and electrochemical limitations of ZnO constrain its effectiveness. Typically, NiO can compensate these inherent defects in ZnO, thereby enhancing the performance of field-emitting devices. In this research, NiO-decorated ZnO thin films were fabricated on diamond surfaces using hydrothermal/sol-gel two-step method. The impact of varying Ni doping concentrations caused by nickel acetate solutions on the field emission properties was thoroughly investigated. Furthermore, this study involved the fabrication of NiO-decorated ZnO/micron diamond heterojunction composite structures, exploring the impact of the structure on the optoelectronic performance of the devices. The Ni doping concentration increases in the NiO films formed between the ZnO nanorods, the doped Ni exists in the ZnO/MCD composite structure as both Ni2+ and Ni3+, which are important materials for semiconductor electronic devices. The NiO decoration process induced the creation of defect levels within the bandgap of the nanorod array structure, consequently enhancing the photoluminescence performance of ZnO. Furthermore, the interaction between NiO and ZnO facilitated the formation of a p-n junction at the interface, generating an internal electric field. This electric field significantly improved the current conduction field and maximum current density of ZnO, thereby enhancing its electric field emission performance. The optical and electrical properties of ZnO nanorods doped at 0.1M exhibited the most favorable characteristics among all tested samples. At a doping concentration of 0.1 M, the turn-on electric field reaches a minimum value of 0.96 V/μm and the maximum current density J reaches a maximum value of 2.54 mA/cm2. These results offer novel insights for advancing the development of integrated broadband optical devices.

Optimizing optoelectronics performance: theoretical and experimental study on ZnO thin film for Al/ZnO/p-Si photodiode

Abstract In this paper, a ZnO photodiode in a p-n heterojunction configuration is fabricated on a p-type Si substrate focusing specifically on ZnO/p-Si heterojunction photosensitive devices and photodiodes (PDs) using Al contacts. Through an experimental and theoretical analysis approach aims to evaluate the effects of important parameters, including ZnO layer thickness, defect density, and contact materials, on PD’s efficiency. Numerical analysis simulations comparatively examine the experimentally fabricated device performance at a 5 nm ZnO layer thickness by balancing photon absorption and carrier formation while minimizing carrier transport limitations. Experimentally process, an Atomic Layer Deposition (ALD) system was used to grow ZnO interlayers on one side of the polished Si wafer. Then, Al metallic contacts were created on the ZnO layers using a hole array mask. The PDs were then subjected to electrical characterization using I-V and I-t measurements under various illumination densities. Al/ZnO/p-Si PD’s device with active performance has been produced and analyzed with electrical parameters such as barrier height, photocurrent, spectral response, ideality factor and EQE were derived, analyzed and studied. In conclusion, this work provides a comprehensive understanding of the performance of Al/ZnO/p-Si PD at varying illumination intensities and offering a detailed analysis of key parameters influencing device efficiency for future optoelectronics applications.

Designed Polar Cosolvent-Prepared Zinc Oxide Film for Efficient and Stable Inverted Organic Solar Cells.

Here, a simple method of applying dimethylformamide (DMF) as cosolvent in the sol-gel technology is used to improve the quality of ZnO bulk films. First-principles calculations show that with the addition of polar solvent DMF, the adsorption energy (Eads) between the solvent and Zn(OH)₂ increases from -1.42 to -1.74eV, which can stabilize the existence of Zn(OH)₂, thereby promoting the ZnO synthesis. Besides, the elimination of amine residues in the DMF-ZnO film significantly suppress the photocatalytic activity induced by amine-induced coordination or redox reactions. Inverted organic solar cells (OSCs) based on PM6:Y6 and PM6:BTP-eC9 achieves impressive power conversion efficiencies (PCE) of 17.58 and 18.14%, respectively. Furthermore, benefiting from the reduced defects of bulk ZnO, pseudo-bilayer bulk heterojunction (PBHJ) devices based on the optimized ZnO film exhibited superior stability, the PM6:Y6 devices based on DMF-ZnO ETLs can maintain 90.28% of their initial PCE after 1000 h of thermal aging at 85°C, and 80.98% of their initial PCE after 168 h of UV aging. This simple solvent optimization strategy can significantly improve the charge transport of ZnO bulk films, making it a reliable strategy for the preparation of electron transport layers in OSCs.

Solution-processed quantum dot short-wavelength infrared photodetectors via integrating 2D MXenes into electron transport layer

Solution-processed quantum dots (QDs) have attracted intensive attention in short-wavelength infrared (SWIR) photodetectors due to their excellent optical properties and tunable size-dependent bandgap. However, the intrinsic defects of the widely used ZnO electron-transport layer (ETL) and the inappropriate band alignment at the interface between the ETL and photoactive QDs inevitably impact the optoelectronic performance of the photodetector. Herein, a high-performance self-powered SWIR photodetector is developed by using 2D Ti3C2 MXenes to passivate the defects of ZnO ETL and to tailor the band alignment at the interface of the ETL/photoactive layer through interface engineering. As a result, the SWIR photodetectors demonstrate the ultra-high light-to-dark current (Ilight/Idark) ratio of ∼ 105 and the low dark current density of 8.33 × 10-4 mA/cm2, and the high specific detectivity (D*) of 1.99 × 1011 Jones at 0 V. By the systematic characterizations, it is proofed that 2D MXene can efficiently passivate defects in ZnO and optimize the alignment of energy levels between the ETL and photoactive layer, which will suppress the recombination of electrons and holes and eventually promote photogenerated carrier transfer at the interface and thus improve device performance. This work revealed that the high-performance solution-processed QD based SWIR photodetector enabled by interface engineering will promote the development of optoelectronic devices in the future.

Reduced Persistent Photoconductivity in Successive Ionic Layer Adsorption and Reaction‐Deposited ZnO:Sn Thin Films

Device‐quality Sn‐doped ZnO thin films are obtained from a simple and cost‐effective successive ionic layer adsorption and reaction method with doping concentrations of 1, 3, 5, and 7 mol%. The influence of doping on the structural, morphological, and optoelectronic properties is studied. All the samples show a hexagonal wurtzite structure with planes that reorient themselves upon doping. Morphological studies reveal sharp cone‐like structures branching out to become florets upon doping, resulting in a higher surface‐to‐volume ratio that is reflected in the photoresponse characteristics. The optical properties show a sharp absorbance edge, in the near‐UV region, for all the samples. The calculated bandgap is in the range of 3.19–3.23 eV. Photoluminescence spectra are recorded to analyze the defect states in the samples, and the native defects of ZnO are found. A remarkable increase in current is observed upon illumination indicating significant photoresponse. ZnO tends to show persistent photoconductivity wherein there is delayed decay in the photocurrent. This phenomenon is reduced significantly herein by doping with Sn atoms. The spectral response study confirms that the devices are suitable for visible‐blind, near‐UV detection.

Towards Atomic Imaging and Spectroscopy of Er defects in ZnO

Towards Atomic Imaging and Spectroscopy of Er defects in ZnO

Sensing reaching the stars: mild condition ZnO defect development for vitamin detection

Sensing reaching the stars: mild condition ZnO defect development for vitamin detection

Passivation of interfacial defects of ZnO and CsPbBr3 by inserting NaSCN in all-inorganic perovskite solar cells

Passivation of interfacial defects of ZnO and CsPbBr3 by inserting NaSCN in all-inorganic perovskite solar cells

High-efficiency photocatalyst based on Au nanoparticles loaded on defective ZnO nanorods

Optimizing the semiconductor-metal interaction is the key to developing metal single-atom cocatalysts with 100 % metal atom utilization and unique electronic properties. Metal atom sites are exclusively coordinated with semiconductor, featuring a chemical-bond-driven tunable interaction. Here vacancy defect-rich ZnO nanorods (NRs) are fabricated by a facile hydrothermal approach. Au nanoparticles (NPs) are preferentially anchored on surface zinc vacancy sites of ZnO NRs in an ultra-low concentration (10−4 mol/L) of HAuCL4 solution. The Au/ZnO nanohybrids exhibit an excellent photocatalytic activity toward removal of Rhodamine B and levofloxacin. Combining ferromagnetism and valence-band XPS spectra analysis, it is demonstrated that the strong interaction of surface vacancy defects in ZnO and Au generates a distinct upshift of the valence band edge, resulting from the antibonding interaction between O 2p and Au 5d orbitals which significantly weakens the Au–O bonds. This facilitates the release of the lattice oxygen and thus generates more oxygen vacancies. The remarkable photoactivity of defective Au/ZnO is due to the synergistic interaction between the intrinsic oxygen vacancy and Au. Optimizing the hybridization of transition metal d and O 2p states at the atomic scale can induce more active-sites, improve atomic utilization efficiency and thus provide a new approach for enhancing photoactivity.

Effect of temperature on the structure, catalyst and magnetic properties of un-doped zinc oxide nanoparticles: experimental and DFT calculation.

Zinc oxide nanoparticles were synthesized using sol-gel and hydrothermal techniques and characterized at different calcination temperatures (400, 500, and 600 °C). The study included an analysis of morphology, crystalline phase, particle size, elemental analysis, specific surface area and chemical state. Various characterization methods were employed, including scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray powder diffraction (XRD), surface analysis (BET), nitrogen absorption and desorption (N2-desorption), Fourier transform infrared spectroscopy (FTIR), thermal analysis (TGA-DSC), temperature-programmed reduction of hydrogen (H2-TPR). Additionally, magnetic properties ZnO nanoparticles were investigated by electron spin resonance (ESR). The investigation revealed changes in reduction behavior, electron spin states, and magnetic properties. The interplay between defects, crystallization, and stability underscores the complexity of ZnO-NPs. These findings contribute to our understanding of nanomaterials and their potential applications in various fields. Density Functional Theory (DFT) calculations with a Hubbard U correction were performed to investigate native defects in ZnO and ZnOCH structures under oxygen-poor (low temperature), oxygen-rich (high temperature) and equilibrium (average temperature) conditions. The formation energies of native defects were calculated, and ESR spectra were simulated to analyze the presence and absence of C[double bond, length as m-dash]O, C-O, CH, and OH bands, as well as to identify the native defects present during growth. The results of the formation energy calculations and the simulated ESR spectra showed that the growth environment influences the native defects that occur during the ZnO preparation process. Inconsistencies between the calculation of formation energy and the ESR spectra suggested that the C[double bond, length as m-dash]O, C-O, CH, and OH bands were negligible and could be disregarded in the ZnO nanoparticles. The findings from this study contribute to a deeper understanding of ZnO-NPs, enabling the optimization of their properties for specific applications, such as effective catalysts in chemical reactions.

Multi-colour emission from ZnO[SO4]:Eu2+ nanophosphors: Effects of SO42- and Eu2+ doping concentration

Blue-emitting ZnO-SO4:Eu2+ powder phosphors were synthesized via solid state reaction method. Based on the X-ray diffraction (XRD) data, hexagonal wurtzite structures of ZnO were formed. Further structural elucidation via Raman spectroscopy showed a peak at 439 cm−1 associated with E2hgh optical mode that is a distinctive characteristic band of hexagonal wurtzite ZnO phase. The ZnO powders were composed of distorted spherical nanoparticles, which were agglomerated together as confirmed from scanning electron microscopy images. After incorporation of SO42- and Eu2+ into the ZnO lattices sites, the particle shapes became irregular. When excited at 351 nm with Xenon lamp, our samples emitted UV and blue-green visible light associated, respectively, with excitonic recombination and intrinsic structural lattice defects in ZnO. Both the photoluminescence (PL) peak intensity and positions of these emissions were influenced by SO42- and Eu2+ ions. The blue emission was dependent on the Eu2+ content with the largest intensity measured from the sample doped with 1.0 mol% of Eu2+ ions. Mechanisms of energy transfer and concentration quenching effect are discussed.

Naphthalimide Molecular‐Doped Zinc Oxide Cathode Interfacial Layer Inhibits Charge Trapping in Organic Solar Cells

So far, the recombination center of photogenerated carriers caused by surface defects in ZnO results in poor thickness tolerance and inefficient charge extraction, severely limiting the performance and stability of inverted organic solar cells (OSCs). Therefore, hybrid cathode interfacial layers (CILs) are fabricated in devices by doping naphthalimide‐based molecules (NE and NDA) into ZnO, and significantly improved performance and stability are achieved for all tested devices. It is found that doping NE or NDA not only solves the problems of ZnO aggregation and surface defects, but also enhances the ability of charge transfer and lowers the work function of cathode. As a result, the OSCs based on PM6:Y6 with ZnO:NE 1% as a CIL exhibit the highest power conversion efficiency (16.72%), which is better than that of pristine ZnO. The research shows that N atoms in naphthalimide react with Zn ions, and −NH bonds form noncovalent interaction with heteroatoms in the blend, which is conducive to the formation of better chemical bond in hybrid materials and providing more transfer channels for carriers. This study highlights a promising strategy for enhancing the performance of inverted OSCs by the hybrid CIL strategy.

Strategic enhancement of oxygen defects in ZnO from ZnS for water splitting to generate green electricity by hydroelectric cell

The green energy produced by the material device Hydroelectric Cell possesses a huge potential to transform the energy generation by water splitting. It is an efficient, clean and green electricity generating device accomplishing the ambitious Net Zero target. The present study reports a facile and unique process to obtain highly defective and nanoporous ZnO for water splitting at room temperature by strategic heat treatment of ZnS and lithium substituted ZnS. The creation of defects enhanced microstrain and dislocation density in ZnO has been confirmed by X-ray diffraction analysis. Surface and lattice defects presence have been distinctly evidenced by photoluminescence (PL) spectroscopy. The oxygen vacancy in ZnO and Li-ZnO has been also confirmed by the g value of 2.06 and 2.09 calculated from electron paramagnetic resonance (EPR) measurements. As soon as water is sprinkled on the Hydroelectric cell, the surface defects chemidissociate water into H3O+ and OH− ions. Hydronium ions trapped in nanopores create a high electric potential that sustains water splitting. Due to redox reactions at electrodes of Hydroelectric cell, voltage and electric current is generated. The fabricated hydroelectric cells (4 cm2 area) of pristine ZnO, ZnS converted ZnO, and Li-ZnO exhibited short circuit current, ISC 5.6 mA, 15 mA and 53 mA respectively by instant water splitting. Innovative method of oxygen defects creation in ZnO by heat treatment of bulk ZnS is an environment friendly, novel and simple non-photocatalytic technique to generate green electricity by water splitting at room temperature.

Efficient PbSe Quantum Dot Infrared Photovoltaic Applying MXene Modified ZnO Electron Transport Layer

AbstractInfrared (IR) solar cells are potential optoelectronic devices for boosting the power conversion efficiency (PCE) of conventional photovoltaics (such as pervoskite and silicon solar cells) by broadening the utilization range of the sunlight spectrum to short‐wavelength infrared region. PbSe colloidal quantum dots (QDs) are one of the optimal candidates for IR solar cells because of their tunable bandgap in the IR region and flexible solution processibility. At present, the best PbSe QD IR photovoltaics generally adopt ZnO as an electron transport layer (ETL). However, the intrinsic drawbacks and surface defects of ZnO can potentially deteriorate the PCE of devices. Herein, Ti3C2Tx, a representative 2D transition carbide, is combined with sol‐gel ZnO to develop a new hybrid ETL for fabricating high‐performance IR solar cells. This combination effectively suppresses the defects within ZnO by forming new bondings and simultaneously enhances the crystalline of ZnO film. Meanwhile, the introduction of Ti3C2Tx into ZnO film accelerates the transport and collection of photo‐generated carriers by constructing a new electron transport pathway. Consequently, compared to the bare devices, the infrared PCE of PbSe QD solar cells increases by 19.5% to 1.04%. These results demonstrate that this hybrid ETL can offer a bright approach for developing high‐performance optoelectronic devices.

Suppression of Visible Emission in Low-Temperature Synthesized Cobalt-Doped ZnO Nanoparticles and Their Photosensing Applications.

Cobalt (Co)-doped ZnO nanoparticles have been synthesized at 100 °C using a simple chemical technique, without post-deposition annealing. These nanoparticles are of excellent crystallinity and show a significant reduction in defect density upon Co-doping. By varying the Co solution concentration, it is observed that oxygen-vacancy-related defects are suppressed at lower Co-doping, while the defect density shows an increasing trend at higher doping densities. This suggests that mild doping can significantly suppress the defects in ZnO for electronic and optoelectronic applications. The effect of Co-doping is studied using X-ray photoelectron spectroscopy (XPS), photoluminescence (PL), electrical conductivity, and Mott-Schottky plots. Photodetectors fabricated using pure and Co-doped ZnO nanoparticles show a noticeable reduction in the response time upon Co-doping, which again affirms the reduction in the defect density after Co-doping.

Melamine-Assisted Thermal Activation Method for Vacancy-Rich ZnO: Calcination Effects on Microstructure and Photocatalytic Properties.

Defect engineering is considered an effective method to adjust the photocatalytic properties of materials. In this work, we synthesized the vacancy-rich ZnO rods with (100) planes via the melamine-assisted thermal activation method. A high concentration of oxygen vacancies was successfully introduced into non-polar oriented ZnO rods by calcination. The effect of oxygen vacancy on the photocatalytic properties of non-polar-oriented ZnO rods was investigated. Raman and XPS spectra revealed the formation of oxygen vacancies in the ZnO. The results showed that the growth habit and defects in ZnO can be controlled by changing the ratio of ZnO to melamine. The higher ratio of ZnO to melamine led to more amounts of (100) planes and oxygen vacancies in ZnO, and it reached the highest when the ratio was 1.2:1. When the ratio was 1.2:1, ZnO exhibited a high methyl orange degradation rate (95.8%). The differences in oxygen vacancy concentration and non-polar planes were responsible for the improvement in photocatalytic performance. ZnO exhibited good stability and regeneration capacity. After recycling four times, the degradation rate was still at 92%. Using the same method, vacancy-rich α-Fe2O3 was obtained. This work could offer a new and simple strategy for designing a photocatalyst with oxygen vacancies.

Revealing the Dependency of Dye Adsorption and Photocatalytic Activity of ZnO Nanoparticles on Their Morphology and Defect States.

ZnO is an effective photocatalyst applied to the degradation of organic dyes in aqueous media. In this study, the UV-light and sunlight-driven photocatalytic activities of ZnO nanoparticles are evaluated. A handheld Lovibond photometer was purposefully calibrated in order to monitor the dye removal in outdoor conditions. The effect of ZnO defect states, i.e., the presence of zinc and oxygen defects on the photocatalytic activity was probed for two types of dyes: fuchsin and methylene blue. Three morphologies of ZnO nanoparticles were deliberately selected, i.e., spherical, facetted and a mix of spherical and facetted, ascertained via transmission electron microscopy. Aqueous and non-aqueous sol-gel routes were applied to their synthesis in order to tailor their size, morphology and defect states. Raman spectroscopy demonstrated that the spherical nanoparticles contained a high amount of oxygen vacancies and zinc interstitials. Photoluminescence spectroscopy revealed that the facetted nanoparticles harbored zinc vacancies in addition to oxygen vacancies. A mechanism for dye degradation based on the possible surface defects in facetted nanoparticles is proposed in this work. The reusability of these nanoparticles for five cycles of dye degradation was also analyzed. More specifically, facetted ZnO nanoparticles tend to exhibit higher efficiencies and reusability than spherical nanoparticles.

Increase the current density and reduce the defects of ZnO by modification of the band gap edges with Cu ions implantation for efficient, flexible dye-sensitized solar cells (FDSSCs)

Flexible dye-sensitized solar cells (FDSSCs) have good potential in future photovoltaic technology. The spin coating method deposited the ZnO films on indium-tin-oxide-coated polyethylene terephthalate (ITO-PET) flexible plastic substrates. These films are implanted with Cu-ions with 1 × 1013 ions/cm2, 1 × 1014 ions/cm2, and 1 × 1015 ions/cm2. All the films have a hexagonal structure. The film irradiated with 1 × 1014 ions/cm2 showed high crystallinity and crystallite size. Important optical properties like bandgap energy (Eg), band edges, refractive index, extinction coefficient, and dielectric constants are measured by UV–Vis spectroscopy. Bandgap energy decreases, and the refractive index increases at the fluence of Cu ions. The maximum decrease in Eg is observed at the 1 × 1014 ions/cm2 dose. Photoluminescence spectra suggest that defects-related emission peaks are decreased at 1 × 1014 ions/cm2 Cu ions fluency. J-V measurements have significantly improved photovoltaic performance compared to pristine ZnO-based solar cells. The highest efficiency (2.30%) is observed at a 1 × 1014 ions/cm2 dose. The efficiency increase is related to improving the charge transfer ratio and shifting the fermi level toward the conduction band.