Zinc Oxide Interface Research Articles

Constructing epoxy and imidazole dual-functionalized polyurethane@Zinc oxide core-shell crosslinker based on coordination interactions for the preparation of strong, tough, and water-resistant soybean flour adhesives

Nanofilling has been regarded as an effective strategy to enhance adhesion performances of soybean flour (SF) adhesives, while it still exists huge challenges to regulate the interfacial properties of nanocomposites toward strong, tough, and water-resistant system. Here, we report on engineering interfacial crosslinking of nanohybrid and SF matrix via core–shell structure design. The reactive core–shell nanohybrid is prepared by epoxy and imidazole dual-functionalized polyurethane shell and zinc oxide (ZnO) nanofiller core under deposition effect of interfacial coordination interactions. Combining reactive epoxy groups and dynamic imidazole/ZnO bonds, a high-performance crosslinking structure with energy dissipation mechanism has been constructed at the interface of ZnO and SF matrix. The structure not only improves the stability of SF adhesive network to resist the external destruction of stress and moisture but also provides dynamic imidazole/metal cation coordination bonds as sacrificial units to facilitate energy dissipation during loading. Results show that the adhesives modified by 5 wt% core–shell nanohybrid present the best performances, in which an 142.0%, 162.3%, and 283.6% increment are observed in dry adhesion strength, wet adhesion strength, and adhesion toughness compared to pristine SF adhesives. Overall, such a high-performance biomass-derived adhesive has great potential for the practical use in wood industry.

The neglected influence of zinc oxide light‐soaking on stability measurements of inverted organic solar cells

AbstractAlthough zinc oxide (ZnO) is one of the most commonly used materials for electron transport layers in organic solar cells (OSCs), it also comes with disadvantages such as the so‐called light‐soaking issues, i.e., its need for exposure to UV light to reach its full potential in OSCs. Here, the impact of ZnO light‐soaking issues on stability measurements of OSCs is investigated. It is found that in the absence of UV light a reversible degradation occurs, which is independent of the used active layer material and accelerates at higher temperatures but can be undone with a short UV exposure. This reversible aging is attributed to the re‐adsorption of oxygen, which for manufacturing reasons is trapped at the interface of ZnO, even in an oxygen‐free environment. This oxygen can be removed with a UV pretreatment of the ZnO but at the expense of device efficiency and production that has to take place in an oxygen‐free environment. This study establishes that stability measurements of ZnO‐containing OSCs must be performed exclusively with a light source including a UV part since the usage of a simple white light source – as often reported in the literature – can lead to erroneous results.

Stacked vanadium pentoxide–zinc oxide interface for optically-chargeable supercapacitors

Photo-chargeable supercapacitor from a ZnO and V2O5 layered structure under UV illumination.

Modification of Electrode Interface with Fullerene-Based Self-Assembled Monolayer for High-Performance Organic Optoelectronic Devices

Efficient charge transfer between organic semiconductors and electrode materials at electrode interfaces is essential for achieving high-performance organic optoelectronic devices. For efficient charge injection and extraction at the electrode interface, an interlayer is usually introduced between the organic active layer and electrode. Here, a simple and effective approach for further improving charge transfer at the organic active layer–interlayer interface was presented. Treatment of the zinc oxide (ZnO) interlayer, a commonly used n-type interlayer, with a fullerene-based self-assembled monolayer (SAM) effectively improved electron transfer at the organic–ZnO interface, without affecting the morphology and crystalline structure of the organic active layer on the cathode interlayer. Furthermore, this treatment reduced charge recombination in the device, attributed to the improved charge extraction and reduction of undesirable ZnO-donor polymer contacts. The photocurrent density and power conversion efficiency of organic solar cells employing the fullerene-SAM-treated interlayer were ~10% higher than those of the device employing the nontreated interlayer. This improvement arises from the enhanced electron extraction and reduced charge recombination.

In Situ Ethanolamine ZnO Nanoparticle Passivation for Perovskite Interface Stability and Highly Efficient Solar Cells.

Zinc oxide (ZnO) has interesting optoelectronic properties, but suffers from chemical instability when in contact with perovskite interfaces; hence, the perovskite deposited on the top degrades promptly. Surface passivation strategies alleviate this instability issue; however, synthesis to passivate ZnO nanoparticles (NPs) in situ has received less attention. Here, a new synthesis at low temperatures with an ethanolamine post treatment has been developed. By using ZnO NPs prepared with ethanolamine and butanol (BuOH), (E-ZnO), the stability of the FA0.9Cs0.1PbI3 (FACsPI)–ZnO interface was achieved, with a photoconversion efficiency of >18%. Impedance spectroscopy demonstrates that the recombination at the interface was reduced in the system with E-ZnO/perovskite compared to common SnO2/perovskite and that the quality of the perovskite on the top is clearly due to the ZnO in situ passivation with ethanolamine. This work extends the use of E-ZnO as an n-type charge extraction layer and demonstrates its feasibility with methylammonium perovskite. Moreover, this study paves the way for other in situ passivation methods with different target molecules, along with new insights regarding the perovskite interface rearrangement when in contact with the modified electron transport layer (ETL).

Copper–zinc oxide interface as a methanol-selective structure in Cu–ZnO catalyst during catalytic hydrogenation of carbon dioxide to methanol

The proper contact of zinc oxide and copper phases is essential achieving high activity/selectivity toward methanol in the Cu–ZnO system.

Defect density and performance influenced by ozone treatment of ZnO interface in inverted organic solar cell

Zinc oxide (ZnO) has great potential as an electron transport layer (ETL) for producing efficient and stable organic solar cells. The effect of ozone treatment on ZnO working as the ETL in the organic solar cell has been studied by analyzing crystallinity, the defect density of states, and charge carrier dynamics from transient absorption spectroscopy to understand its role in the improvement in the interface between ETL and active layers. We have observed that a 10-minute continuous ozone treatment of ZnO film demonstrates improvement in its crystallinity leading to a 23% increment in short circuit current. The improvement in the crystallinity has been confirmed by the morphological and structural analysis using SEM and GIXRD. These analyses reveal the formation of a flake-like structure and an increase in peak intensity in GIXRD. It has been observed that ozone exposure has significantly affected the carrier recombination resistance, ideality factor of the device. From transient absorption spectroscopy, it has been found that for 10 min ozone-treated ZnO film has an average carrier transport time (661.79 ps), which is smallest as compared to untreated film or over treated film leading to faster carrier extraction through ETL. Further, the study of defect density of states shows that optimized ozone-treated film show 22.08% decrease in defects as compared to the control device, which primarily reflected as the improvement in the current density leading to increase in device efficiency from 2.95% to 3.75%.

Fabrication of ZnO interface layer from a novel aqueous sol-gel precursor solution for organic solar cells

To improve the morphology and charge transport property of zinc oxide (ZnO) interface layer in the field of organic solar cells (OSCs), a novel ZnO sol-gel precursor was developed by redox reaction among zinc powder (Zn), hydrogen peroxide (H2O2), and ammonia (NH3·H2O) in aqueous solvent. This aqueous ZnO sol-gel precursor has advantages in cost and stability. Furthermore, photoelectric conversion performance of OSCs with ZnO layer (aqueous) is better than that of device with ZnO layer (nonaqueous). To further elaborate the relevance between the ZnO interface layer and the device performance, optical and morphology characteristics of precursor solutions, ZnO layers, and active layers were studied. Meanwhile, electrical characteristics of the OSCs were also analyzed. The results show less anion and larger colloidal particle size in aqueous sol-gel solution, which making the ZnO interface layer have fewer defects and larger surface roughness than nonaqueous-phase prepared ZnO layer. Thus, free electron could transfer from the active layer to ZnO layer more easily, and charge recombination is reduced at the interface. Moreover, the electron mobility of OSCs is also enhanced by the aqueous-phase prepared ZnO layer. Therefore, short-circuit current and photoelectric conversion performance of device are promoted.

Heterojunction interface of zinc oxide and zinc sulfide promoting reactive molecules activation and carrier separation toward efficient photocatalysis

Heterojunction photocatalysts, which can alleviate the low carrier separation efficiency and insufficient light absorption capacity of a single catalyst, have received widespread attention. However, the specific interfacial structure of the heterojunction and its effect on the photocatalytic reaction is still unclear. Herein, a battery of zinc oxide/zinc sulfide (ZnO@ZnS) heterojunction microspheres with different degrees of sulfuration were successfully constructed via a facile hydrothermal method. The as-prepared photocatalysts shown decent aerobic nitric oxide (NO) oxidation performance under visible light irradiation, and the results of various characterization techniques illustrated that the superior photoactivity could be ascribed to the spatial separation of photoinduced electron-hole pairs due to the synergy of the internal electric field and the band offset. More importantly, density functional theory (DFT) calculations revealed that the heterojunction interface can significantly promote the generation of reactive oxygen species (ROS) and NO+ reaction intermediates and thus accelerate the photocatalytic reaction. Finally, in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) technology was used to time-dependently monitor the NO oxidation process, revealing the photocatalytic mechanism. This work investigated the role of the heterojunction interface in the gas-phase catalytic reaction, broadening the practical application of the ZnO@ZnS heterojunction.

Thermal Evaporation–Oxidation Deposited Aluminum Oxide as an Interfacial Modifier to Improve the Performance and Stability of Zinc Oxide-Based Planar Perovskite Solar Cells

The acid–base chemistry at the interface of zinc oxide (ZnO) and methylammonium lead tri-iodide (perovskite) leads to a proton transfer reaction that results in perovskite degradation. In perovskit...

Charge transfer induced excitons and nonlinear optical properties of ZnO/PEDOT:PSS nanocomposite films.

In this current work, we have prepared zinc oxide (ZnO) nanorods by sol-gel method, and its composite films with a conducting polymer poly (3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) also have been prepared by drop-casting method on the glass substrate. UV-Vis absorption and steady-state fluorescence studies revealed exciton dissociation and recombination at the interface of polymer chain and wide-bandgap semiconductor ZnO. Also, nonlinear optical properties of as-prepared nanocomposite films have been reported by employing an open aperture z-scan technique. A predominantly two-photon induced saturable absorption behavior, when excited with 532nm, 10ns laser pulses, appeared in nonlinear optical measurements. These results indicate that our as-synthesized composites can be useful in fabricating optical switch and saturable absorbers.

Potassium-Presenting Zinc Oxide Surfaces Induce Vertical Phase Separation in Fullerene-Free Organic Photovoltaics.

Bulk heterojunction (BHJ) structure based organic photovoltaics (OPVs) have recently showed great potential for achieving high power conversion efficiencies (PCEs). An ideal BHJ structure would feature large donor/acceptor interfacial areas for efficient exciton dissociation and gradient distributions with high donor and acceptor concentrations near the anode and cathode, respectively, for efficient charge extraction. However, the random mixing of donors and acceptors in the BHJ often suffers the severe charge recombination in the interface, resulting in poor charge extraction. Herein, we propose a new approach-treating the surface of the zinc oxide (ZnO) as an electron transport layer with potassium hydroxide-to induce vertical phase separation of an active layer incorporating the nonfullerene acceptor IT-4F. Density functional theory calculations suggested that the binding energy difference between IT-4F and the PBDB-T-2Cl, to the potassium (K)-presenting ZnO interface, is twice as strong as that for IT-4F and PBDB-T-2Cl to the untreated ZnO surface, such that it would induce more IT-4F moving toward the K-presenting ZnO interface than the untreated ZnO interface thermodynamically. Benefiting from efficient charge extraction, the best PCEs increased to 12.8% from 11.8% for PBDB-T-2Cl:IT-4F-based devices, to 12.6% from 11.6% for PBDB-T-2Cl:Y1-4F-based devices, to 13.5% from 12.2% for PBDB-T-2Cl:Y6-based devices, and to 15.7% from 15.1% for PM6:Y6-based devices.

Nanostructural and barrier property characterization of ZnO/PEDOT:PSS heterojunction by adjusting RF power in the magnetron sputtering deposition technique

Nanostructure and barrier properties of the heterojunction formed at the interface of ZnO/PEDOT:PSS inorganic/organic contact have been investigated. The PEDOT:PSS layer and the zinc oxide nanostructures have been deposited using the spin coating and the radio frequency magnetron sputtering techniques on glass substrates at room temperature, respectively. Particularly, the effects of zinc oxide sputtering power on the nanostructure properties of the deposited layer are investigated. The deposition power varies from 60 to 240 W. AFM results show that increasing the deposition power, results in the grain size and the surface roughness of the zinc oxide layer to increase. The energy gap measured for the zinc oxide layers deposited at the powers of 60, 120, 180 and 240 W was 3.24, 3.23, 3.18, and 3.20 eV, respectively. In order to investigate the heterojunction formed at the interface of zinc oxide and poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT: PSS), a polymeric layer of thickness of 50 nm is deposited on a 300-nm zinc oxide layer. The dark I–V characteristics indicate that the reverse saturation current density is 5.01 × 10−7, 3.16 × 10−5, 1.96 × 10−7 and 7.98 × 10−7 A/cm2 for the deposition power of 60, 120, 180, and 240 W, respectively. By increasing the deposition power the ideality factor of the resulting Schottky barrier is 3.2, 2.9, 2.3 and 3.6. The effective Schottky barrier heights of 0.76, 0.77, 0.78, and 0.75 eV were obtained for the same order of deposition powers. It was found that the highest optical response could be obtained for the samples prepared at the deposition power of 180 W.

Overcoming Zinc Oxide Interface Instability with a Methylammonium‐Free Perovskite for High‐Performance Solar Cells

AbstractPerovskite solar cells have achieved the highest power conversion efficiencies on metal oxide n‐type layers, including SnO2 and TiO2. Despite ZnO having superior optoelectronic properties to these metal oxides, such as improved transmittance, higher conductivity, and closer conduction band alignment to methylammonium (MA)PbI3, ZnO is largely overlooked due to a chemical instability when in contact with metal halide perovskites, which leads to rapid decomposition of the perovskite. While surface passivation techniques have somewhat mitigated this instability, investigations as to whether all metal halide perovskites exhibit this instability with ZnO are yet to be undertaken. Experimental methods to elucidate the degradation mechanisms at ZnO–MAPbI3 interfaces are developed. By substituting MA with formamidinium (FA) and cesium (Cs), the stability of the perovskite–ZnO interface is greatly enhanced and it is found that stability compares favorably with SnO2‐based devices after high‐intensity UV irradiation and 85 °C thermal stressing. For devices comprising FA‐ and Cs‐based metal halide perovskite absorber layers on ZnO, a 21.1% scanned power conversion efficiency and 18% steady‐state power output are achieved. This work demonstrates that ZnO appears to be as feasible an n‐type charge extraction layer as SnO2, with many foreseeable advantages, provided that MA cations are avoided.

Low-Temperature and Solution-Processable Zinc Oxide Transistors for Transparent Electronics.

Zinc oxide (ZnO) thin-film transistors (TFTs) have many promising applications in the areas of logic circuits, displays, ultraviolet detectors, and biosensors due to their high performances, facile fabrication processing, and low cost. The solution method is an important technique for low-cost and large fabrication of oxide semiconductor TFTs. However, a key challenge of solution-processable ZnO TFTs is the relatively high processing temperature (≥500 °C) for achieving high carrier mobility. Here, facile, low-cost, and solution-processable ZnO TFTs were fabricated under the annealing temperature of ≤300 °C. Dense and polycrystalline ZnO films were deposited by the spin-coating method. The ZnO TFTs showed the maximum electron mobility of 11 cm2/V s and a high on/off ratio of >107 when the ZnO thin films were annealed at 300 °C. The mobility was extremely high among solution-processable undoped ZnO TFTs reported previously, even better than some high-cost indium-doped ZnO TFTs fabricated at low temperature. Furthermore, it is found that the mechanism of oxygen vacancies dominates the electron transport in ZnO thin film and interface behaviors of ZnO thin film and SiO2 gate insulator, and then dominates the performances of devices.

Solution‐Processed Double‐Layer Electron‐Transport Layer for Conventional Blue Phosphorescent Organic Light‐Emitting Diodes

Zinc oxide (ZnO) is a potential material for the electron‐transport layer (ETL) in organic light‐emitting diodes (OLEDs). However, ZnO may induce exciton dissociation at the emission layer (EML)/ZnO interface, which lowers the device efficiency. Here, polyethyleneimine (PEI)‐doped lithium acetylacetonate (Li(acac)) is used as a hybrid interfacial layer (IL) between a ZnO nanoparticle (NP) ETL and a phosphorescent EML, with a thermally evaporated aluminum film as the cathode contact on the top. To avoid the IL being dissolved, ZnO NPs were re‐dispersed in octane (an orthogonal solvent for most ILs) and doped with trans‐polyisoprene (PI) to prevent aggregation on the film. The hybrid IL markedly improves electron injection and transport and suppresses triplet exciton quenching at the EML/ZnO interface, resulting in a lower driving voltage and doubled luminous efficiency compared with those of the control device without IL. ZnO NPs can serve as an ETL in conventional OLEDs cooperating with PEI‐doped Li(acac) as an IL and this research provides an easy way to construct a stable double‐layer ETL configuration in high‐efficiency OLEDs.

Analysis of ZnO Thin Film as Thermal Interface Material for High Power Light Emitting Diode Application

All solid-state lighting products produce heat which should be removed by use of a heat sink. Since the two mating surfaces of light emitting diode (LED) package and heat sink are not flat, a thermal interface material (TIM) must be applied between them to fill the gaps resulting from their surface roughness and lack of coplanarity. The application of a traditional TIM may squeeze out when pressure is applied to join the surfaces and hence a short circuit may result. To avoid such a problem, a thin solid film based TIM has been suggested. In this study, a zinc oxide (ZnO) thin film was coated on Cu substrates and used as the TIM. The ZnO thin film coated substrates were used as heat sink purposes in this study. The prepared heat sink was tested with 3 W green LED and the observed results were compared with the results of same LED measured at bare and commercial thermal paste coated Cu substrates boundary conditions. The influence of interface material thickness on total thermal resistance (Rth-tot), rise in junction temperature (TJ), and optical properties of LED was analyzed. A noticeable reduction in Rth-tot (5.92 K/W) as well as TJ (ΔTJ = 11.83 °C) was observed for 800 nm ZnO thin film coated Cu substrates boundary conditions when compared with bare and thermal paste coated Cu substrates tested at 700 mA. Change in TJ influenced the thermal resistance of ZnO interface material. Improved lux level and decreased correlated color temperature (CCT) were also observed with ZnO coated Cu substrates.

Multi-oxide active layer deposition using Applied Materials Pivot array coater for high-mobility metal oxide TFT

By controlling a thin indium tin oxide (ITO), indium zinc oxide interface layer between gate insulator and indium gallium zinc oxide (IGZO), the thin-film transistor (TFT) performance can reach higher mobility as conventional IGZO as well as superior stability. For large-area display application, Applied Materials static PVD array coater (Applied Materials GmbH & Co. KG, Alzenau, Germany) using rotary targets has been developed to enable uniform thin layer deposition in display industry. Unique magnet motion parameter optimization in Pivot sputtering coater is shown to provide very uniform thin ITO layer to reach TFT performance with high mobility, not only on small scale, but also on Gen8.5 (2500 × 2200 mm glass size) production system.

Electronic Structure of the Perylene–Zinc Oxide Interface: Computational Study of Photoinduced Electron Transfer and Impact of Surface Defects

The electronic properties of dye-sensitized semiconductor surfaces consisting of perylene chromophores chemisorbed on zinc oxide via different spacer-anchor groups have been studied at the density-functional-theory level. The energy distributions of the donor states and the rates of photoinduced electron transfer from dye to surface are predicted. We evaluate in particular the impact of saturated versus unsaturated aliphatic spacer groups inserted between the perylene chromophore and the semiconductor as well as the influence of surface defects on the electron-injection rates.

High-performance Ge quantum dot decorated graphene/zinc-oxide heterostructure infrared photodetector.

A novel size-controllable germanium quantum dot (Ge QD) is synthesized and decorated onto reduced graphene oxide (RGO) fragments to overcome the low infrared (IR) photoresponses (∼0.1 A/W)13,14 of pristine graphene. With the integration of flexible substrate, monolayer graphene (MLG) electrode and n-type zinc oxide (ZnO), a high-performance QD-decorated-RGO/ZnO heterostructure infrared photodetector is reported in this study. The Ge QD-decorated-RGO hybrid photosensitive composite improves the responsivity (∼9.7 A/W, 1400 nm) in IR waveband without sacrificing the response speed (∼40 μs rise time and 90 μs recovery time). In addition, the effective barrier formed between graphene and ZnO interface restricts the dark current (∼1.4 nA, -3 V) to guarantee the relatively excellent rectifying behavior and high on/off ratio (∼10(3)) for this IR photodetector. With these superior inherent properties and micron-sized sensing active area, this photodetector manifests great potential in the future application of graphene-based IR photodetector.