Zinc Oxide Bilayer Research Articles

Dependence of deposition bath temperature for p-electrodeposited-Cu2O onto n-TiO2/ZnO bilayer thin films

The synthesis of semiconductor materials is crucial to produce the best properties of heterojunction thin films solar cell. Titanium dioxide (TiO2) is coupled with zinc oxide (ZnO) to promote high transmittance due to low utilization of the solar spectrum. In this project, p-Cu2O as absorbing layer was deposited onto n-TiO2/ZnO bilayer thin film which acts as window layer in order to complete the device. Several bath temperatures of 30, 40, 50 and 60 °C were manipulated during Linear Sweep Voltammetry (LSV) measurement and electrodeposition process for p-Cu2O thin film. The LSV measurement was employed to determine the potential value and electrochemical properties of p-Cu2O thin film. Based on findings, the suitable deposition potential chosen is − 0.4 V vs Ag/AgCl. The p-Cu2O thin film deposited at bath temperature of 40 °C exhibited the highest diffraction peak intensity in the (111)-preferred plane orientation showing high crystallinity. The surface morphology of homogeneous and well-defined triangular shape with thickness of 4.93μm was observed. The estimated bandgap energy of 1.92 eV acquired indicated to p-Cu2O thin film. The n-TiO2/ZnO bilayer/p-Cu2O heterojunction thin film was successfully fabricated and showed significant electrical rectification properties. Here in, bath temperature influenced to the enhancement of heterointerface growth development in several properties.

Structural and Electronic Properties of ZnO Bilayer and Twist Bilayer: A First-Principles Study

By using the first principles calculations, we study the structural and electronic properties of zinc oxide (ZnO) bilayers. Initial ZnO bilayer has a planar structure, which is different from bulk ZnO. Another kind of twist ZnO bilayer is designed by rotating 60° on the basis of ZnO bilayer structure with a Zn/O atom as the axis. Both the bilayers have stable structure and high symmetry. As the interlayer distance increases, the interaction of the upper and the lower layers will weaken in both the bilayers. It is Zn atom but not O atom that plays a key role in the interlayer interaction, which has been confirmed by Mulliken charge and density of states results. The band gap of the bilayers can be tuned by translation motion, and ZnO twist bilayer shows a better performance than the initial bilayer in this study. Combining the two factors (interlayer distance and twist angle), ZnO bilayers are very hopeful to be utilized in 3D joints of nanoelectronic devices. Our results provide a detailed understanding of the structural and electronic properties of ZnO bilayers and help to predict the performance of ZnO-based two-dimensional nanoelectronics and nanocomposites.

The role of rGO sheet and Ag dopant in reducing ZnO electron transport layer recombination in planar perovskite solar cells

For planar perovskite solar cells (PSCs) to have satisfactory performance and acceptable stability, an ETL (electron transport layer) is needed that provides a high level of efficiency. It should be noted that when considering the implementation of n-type metal oxide materials, the ZnO (zinc oxide) can be a great choice for an ETL because it provides a relatively high level of mobility. The current study proposes a new design involving a reduced graphene oxide (rGO) sheet/Ag-doped ZnO bilayer to be utilized as ETL in planar PSCs. Extensive experimental and computational analyses including nano-micro structural, optical and electrical properties are carried out in order to compare the performance and governing mechanisms of rGO/Ag-doped bilayer-based planar PSC to ordinary un-doped ZnO. The results from the performed experiments show that using the rGO sheet as the buffer layer and Ag-doped ZnO significantly increase the power conversion efficiency (PCE) by more than 30% compared to un-doped ZnO ETL in planar PSCs. These improvements in the performance of PSCs can be explained based on fine tuning the energy levels of ZnO/perovskite, since this increases the charge-carrier-extraction from the perovskite layer. Moreover, the results of the study confirm the using the rGO/Ag-doped ZnO bilayer ETL as a new methodology for the creation of stable planar PSCs with low charge recombination rate and high performance.

Double Metal Oxide Electron Transport Layers for Colloidal Quantum Dot Light-Emitting Diodes.

The performance of colloidal quantum dot light-emitting diodes (QD-LEDs) have been rapidly improved since metal oxide semiconductors were adopted for an electron transport layer (ETL). Among metal oxide semiconductors, zinc oxide (ZnO) has been the most generally employed for the ETL because of its excellent electron transport and injection properties. However, the ZnO ETL often yields charge imbalance in QD-LEDs, which results in undesirable device performance. Here, to address this issue, we introduce double metal oxide ETLs comprising ZnO and tin dioxide (SnO2) bilayer stacks. The employment of SnO2 for the second ETL significantly improves charge balance in the QD-LEDs by preventing spontaneous electron injection from the ZnO ETL and, as a result, we demonstrate 1.6 times higher luminescence efficiency in the QD-LEDs. This result suggests that the proposed double metal oxide ETLs can be a versatile platform for QD-based optoelectronic devices.

High Figure-of-Merit Transparent Copper–Zinc Oxide Window Electrodes for Organic Photovoltaics

We report a copper - zinc oxide bilayer electrode supported on flexible polyethylene terephthalate (PET) with a sheet resistance of 11.3 Ω sq-1 and average transparency of 84.6 % in the wavelength range of 400 - 800 nm. The copper film is perforated with a dense array of sub-micron diameter apertures fabricated using polymer blend lithography, which imparts broad band anti-reflectivity. We demonstrate proof-of-principle that it is possible to fabricate the polymer mask by dip coating which is a scalable deposition method compatible with roll-to-roll processing. During storage of the electrode at ambient temperature the ZnO layer is spontaneously doped with copper from the underlying copper film and so the thin ZnO layer serves both as an anti-reflecting layer and an excellent electron transport layer. When compared with commercially available indium tin oxide coated (ITO) plastic substrates this electrode exhibits superior stability towards bending deformation, with no change in sheet resistance after bending through a 4 mm radius of curvature one hundred times. Model inverted organic photovoltaic (OPV) devices using this electrode exhibit a champion power conversion efficiency of 8.7%, which is the highest reported efficiency to date for an OPV using a copper based transparent electrode, outperforming identical devices using ITO coated plastic as the transparent electrode.

Electronic Transport Properties Governed by Polarity Control through Tailoring of ZnO Bilayer Structures

It is critical to reveal how crystalline polarity correlates with the electronic transport properties in polar semiconductors, such as zinc oxide (ZnO), for the development of materials with properties tailored for specific optoelectronic applications. In this paper, we investigate the structure–property relationships in ZnO films by means of tailoring the polarity of homostructural ZnO bilayers that are subjected to an external substrate bias (Vsub) during deposition. Since the probability of incorporating defects and impurities in ZnO depend on the crystalline facet, the polarity of ZnO should be a critical parameter in determining electronic conductivity. The electric conductivity and Hall mobility of the ZnO films deposited under positive Vsub were much higher than those deposited under negative Vsub. Further investigations of the homostructural ZnO bilayer films, where different signs and magnitudes of Vsub were applied, revealed that the polarity is responsible for electronic conductivity of the ZnO...

Properties of Al-doped zinc oxide and In-doped zinc oxide bilayer transparent conducting oxides for solar cell applications

Novel aluminum and indium doped zinc oxide (ZnO) bilayer transparent conducting oxide thin films was fabricated by simple sol-gel spin coating method and post-annealed at 500 °C for an hour under nitrogen ambient for solar cell applications. The structural, electrical and optical properties of both the as-deposited and annealed bilayer thin films were characterized. X-ray diffraction studies show a hexagonal wurtzite-type structure of ZnO with (0 0 2) orientation, which enhanced with annealing. In atomic force microscopy studies, minimum surface roughness was attained for Al-doped ZnO (AZO)/In-doped ZnO (IZO) bilayer TCO film compared to IZO/AZO bilayer film. The AZO/IZO film sheet resistance improved to 0.057 M ohm/square after post-annealing, while the single layer AZO film sheet resistance degraded upon annealing in nitrogen atmosphere. All the films had an average transmittance in the visible region over 96%.

A Design Based on a Charge-Transfer Bilayer as an Electron Transport Layer for Improving the Performance and Stability in Planar Perovskite Solar Cells

A highly efficient electron transport layer (ETL) is an essential constituent for good performance and stability in planar perovskite solar cells. Among n-type metal oxide materials, zinc oxide (ZnO) is a promising candidate for an electron transport layer due to its relatively high electron mobility, high transparency, and versatile nanostructures. However, it was found that several disadvantages could occur at the ZnO/perovskite interface, such as decomposition of CH3NH3PbI3 and poorly aligned energy levels. To overcome these issues, we present a design based on staircase band alignment of a low-temperature solution-processed ZnO/Al-doped ZnO (AZO) bilayer thin film as electron transport layers in planar perovskite solar cells. Experimental results revealed that the power conversion efficiency (PCE) of perovskite solar cells was significantly increased from 12.3% to 16.1% by employing the AZO thin film as the buffer layer. Meanwhile, the short-circuit current density (Jsc), open-circuit voltage (Voc), a...

Highly stable and efficient inverted organic solar cells based on low-temperature solution-processed PEIE and ZnO bilayers

Highly efficient and air-stable inverted organic solar cells were fabricated from solution-processed non-conjugated polyethylenimine ethoxylated as the polyelectrolyte, a zinc oxide bilayer as the electron transport layer, and an active layer of PTB7 and PC71BM.

Effect of Annealing Time Process on the pH Sensitivity of Spin-coated TiO2/ ZnO Bilayer Film

This paper presents an investigation on titanium dioxide (TiO2) and zinc oxide (ZnO) bilayer film, which is used as sensing membrane for extended-gate field effect transistor (EGFET) for pH sensing application. TiO2/ZnO thin films were deposited using sol-gel spin coating method on indium tin oxide (ITO) substrates. After the deposition, the bilayer films were annealed at constant temperatures which is 400 °C for 15, 30, 40 and 60 minutes. The sensitivity of the TiO2 thin film towards pH buffer solution was measured by dipping the sensing membrane in pH4, pH7 and pH10 buffer solution. By varying the annealing time, we found that the TiO2/ZnO thin film annealed at 400°C for 15 minutes gave the highest sensitivity compared to other annealing conditions, with the value of 64.87 mV/pH.

Interfacial molecular order of conjugated polymer in P3HT:ZnO bilayer photovoltaics and its impact on device performance

Hybrid (organic-oxide) photovoltaic device performance is highly dependent on the nature and quality of the organic-oxide interface. This work investigates the details of interfacial morphology in terms of the molecular order of poly(3-hexylthiophene) (P3HT) at the planar interface with zinc oxide (ZnO) formed by pulsed laser deposition. Resonant Raman spectroscopy is employed as a powerful morphological probe for conjugated polymers to reveal that the interfacial P3HT is disrupted during the deposition process whereas the bulk polymer shows an increase in molecular order. External quantum efficiency measurements of P3HT:ZnO bilayer devices show that this disordered P3HT region is active in photocurrent generation.

Stable photovoltaic cells based on graphene oxide/indium zinc oxide bilayer anode buffer

We report a solution-processed graphene oxide (GO) functioned as an anode buffer layer in organic photovoltaic cells (OPVs). The OPVs using indium zinc oxide (IZO), IZO/GO, GO/IZO, and poly(3,4-thylenedioxythiophene) doped poly(styrene sulfonate) (PEDOT:PSS) as a control device, exhibited the conversion efficiency of 3.4%, 3.5%, 3.9% and 3.4%, respectively. No obvious degradation was discovered for the OPVs with incorporating GO as one of the anode buffer layers after 1h continuous illumination under AM1.5. On the other hand, after only 1h continuous illumination, a momentous degradation was observed for the OPVs without the presence of GO. All these results demonstrate that the GO layer plays an important role in the improvement of the stability with conventional device architecture.