ZnO Interlayer Research Articles

Study of Interface Resistance of <I>n</I>-ZnO on <I>p</I>-Si Substrate with ZnO Interlayer by Spray Pyrolysis Method

Study of Interface Resistance of <I>n</I>-ZnO on <I>p</I>-Si Substrate with ZnO Interlayer by Spray Pyrolysis Method

Novel Fe3O4@ZnO@mSiO2 Nanocarrier for Targeted Drug Delivery and Controllable Release with Microwave Irradiation

In this paper, we constructed a novel core–shell structured nanocarrier used as a drug carrier to investigate the storage and controllable release properties of the cancer chemotherapeutic drug etoposide (VP16). The new composite nanocomposite composed of a mesoporous silica shell with magnetic Fe3O4 core and ZnO interlayer with a core–shell structure was prepared by a simple process. The mesoporous nanocarrier possesses high surface area (643.9 m2/g), provides large accessible pore volume (0.32 cm3/g) for the adsorption of drug molecules, and has a high magnetization saturation value (56.8 emu/g) for drug targeting under foreign magnetic fields, and the ZnO interlayer acts as a good microwave absorber with excellent microwave thermal response property for microwave-triggered drug release (the VP16 release of over 85% under microwave discontinuous irradiation outclasses the 14% within 10 h only stirring release). This multifunctional system shows a good performance for targeting delivery and controllable ...

Solution-processed nanostructured zinc oxide cathode interfacial layers for efficient inverted organic photovoltaics

Inverted organic photovoltaic (OPV) cells based on poly(3-hexylthiophene) (P3HT) as an electron donor and [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) as an electron acceptor, were fabricated and characterized. To improve the photovoltaic performance, interface control using either dense or nanostructured ZnO films as cathode buffer layers for effective electron transport was demonstrated, while an under-stoichiometric transition metal oxide, such as MoOx, was employed as the anode buffer layer for efficient hole extraction. Incorporation of a nanostructured ZnO interlayer enhanced electron–hole dissociation by enabling a larger interfacial contact with the active layer, that results in increased short-circuit current density (Jsc) and eventually contributing to higher power conversion efficiency (PCE).

Novel silicon surface passivation by Al2O3/ZnO/Al2O3 films deposited by thermal atomic layer deposition

In this paper, a novel Al2O3/ZnO/Al2O3 stack is proposed as the silicon passivation layer for c-Si solar cell application. Recently, the Al2O3 film has been proved to be effective for passivating the p-type c-Si surface by forming the negative fixed oxide charge. It is confirmed by this experiment that the amount of negative fixed oxide charge can be controlled by inserting a ZnO interlayer (IL), which is explained by acceptor-like defect (VZn, Oi, and OZn) formation determined by the room-temperature photoluminescence (RTPL) analysis. The effect of ZnO IL is investigated using Al2O3 bottom layers of various thicknesses by electrical and physical analyses. The effective lifetime measurement shows that the electronic recombination losses at the silicon surface are reduced effectively by optimizing the Al2O3/ZnO/Al2O3 stack.

Using ultra-high molecular weight hydrophilic polymer as cathode interlayer for inverted polymer solar cells: Enhanced efficiency and excellent air-stability

New cathode interlayers based on a water soluble cationic polyacrylamide (C-PAM) with a viscosity-averaged molecular weight of 3 million were introduced as cathode interlayers in inverted solar cells. The neat C-PAM and 5% CsF doped C-PAM thin layers on ITO substrate could decrease the work-function of ITO and hence lead to suitable energy level alignments for efficient electron collection. Obvious enhancements of energy conversion efficiency as well as air-stability were found, in comparison to well-known ZnO interlayer based device. The possible factors involving deteriorations at two interfaces of ITO/interlayer and interlayer/active layer during more than 1 year storage under an ambient condition were analyzed. Our results suggest that the interlayer polymer with giant molecular size and numerous side groups of hydrophilic amide and quaternary ammonium would facilitate the formations of large and intimate single-molecular binding area with the ITO substrate and the upper active layer, and might afford more reliable interfacial contacts to resist possible moisture- and/or stress-induced delamination. Therefore, hydrophilic polymer with an ultra-high molecular weight would be an ideal cathode interlayer for efficient and air-stable inverted solar cells.

Doping Effect of Electron Transport Layer on Nanoscale Phase Separation and Charge Transport in Bulk Heterojunction Solar Cells

We investigated the influence of the Ga doping in the ZnO interlayer as an electron transport layer (ZnO ETL) on the nanoscale phase separation in the bulk heterjunction (BHJ) layer coated on the ETL as well as the morphological and electrical properties of a low temperature sol–gel-derived pristine ZnO ETL (P-ETL) and Ga-doped ZnO ETL (G-ETL), which affect the performance of inverted organic solar cells (IOSCs). X-ray photoelectron spectroscopy (XPS) confirms the successful incorporation of the element Ga in the ZnO ETL. The short circuit current densities (JSC) of IOSCs fabricated using a G-ETL were significantly improved from those of IOSCs fabricated with a P-ETL. The maximum JSC was obtained at 2 at. % Ga doping. The IOSCs fabricated with a 2 at. % G-ETL demonstrated power conversion efficiencies of 3.51% (P3HT:PC60BM) and 5.43% (PCDTBT:PC70BM), which were higher than the power conversion efficiencies of 2.88% (P3HT:PC60BM) and 4.90% (PCDTBT:PC70BM) of the IOSCs fabricated with a P-ETL under simulated air mass 1.5 global full-sun illumination. The better performance was attributed to the improved electrical properties of the G-ETL and the enhanced nanoscale phase separation in the BHJ active layer.

Enhanced performance of polymer solar cell with ZnO nanoparticle electron transporting layer passivated by in situ cross-linked three-dimensional polymer network

An in situ cross-linked three-dimensional polymer network has been developed to passivate ZnO nanoparticles as an electron transporting layer (ETL) to improve the performance of inverted organic solar cells. The passivated ZnO ETL-based devices achieve efficiencies of 3.26% for poly(3-hexylthiophene) (P3HT):[6,6]-phenyl-C61-butyric acid methyl ester (PCBM) and 7.37% for poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl]] (PTB7):[6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) devices compared with 2.58% and 6.67% for the control devices respectively. The origin of the improvement is studied by investigating the influence of the transport barrier, morphology and recombination. Atomic force microscopy (AFM), photoluminescence (PL) and transient photocurrent (TPC) measurements prove the boosted performance originates from the improved film-forming quality as well as passivated defects in the ZnO film, decreasing the trap-assisted recombination rather than giving better energy alignment between the active layer and the ZnO interlayer.

Efficient and ultraviolet durable inverted organic solar cells based on an aluminum-doped zinc oxide transparent cathode

High performance inverted bulk heterojunction organic solar cells (OSCs), based on the blend of poly[[4,8-bis[(2-ethylhexyl)oxy] benzo [1,2-b:4,5-b′] dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl]] (PTB7): 3′H-Cyclopropa[8,25] [5,6]fullerene-C70-D5h(6)-3′-butanoicacid, 3′-phenyl-, methyl ester (PC70BM), were achieved using an aluminum-doped zinc oxide (AZO) front transparent cathode. A structurally identical PTB7:PC70BM-based OSC having an indium tin oxide (ITO) front cathode was also made for comparison studies. The surface of AZO and ITO was modified with a 10 nm thick solution-processed ZnO interlayer to facilitate the efficient electron extraction. This work yielded AZO-based OSCs with a promising power conversion efficiency of 6.15%, slightly lower than 6.57% of a control ITO-based OSC, however, a significant enhancement in the stability of AZO-based OSCs was observed under an ultraviolet (UV)-assisted acceleration aging test. The distinctive enhancement in the lifetime of AZO-based OSCs arises from the tailored absorption of AZO electrode in wavelength <380 nm, serving as a UV filter to inhibit an inevitable degradation in ITO-based OSCs caused by the UV exposure.

Influences of Surface Roughness of ZnO Electron Transport Layer on the Photovoltaic Performance of Organic Inverted Solar Cells

Here, we demonstrate the correlation between the surface roughness of the ZnO interlayer used as an electron transporting interlayer (ETL) in organic inverted solar cells (ISCs) and the photovoltaic performance of the ISCs. Three different surfaces of the ZnO ETL are studied in ISCs with the polymer poly[2,3-bis-(3-octyloxyphenyl)-quinoxaline-5,8-diyl-alt-thiophene-2,5-d iyl] (TQ1) mixed with [6,6]-phenyl C71 butyric acid methyl ester (PC71BM) as the active layer. The results obtained from these ISCs show that power conversion efficiency increases from 2.7% to 3.9% when the root-mean-square roughness of the ZnO layer decreases from 48 to 1.9 nm. Moreover, it is found that the short-circuit current density is higher in the ISC based on the smoother ZnO interlayer, with a larger donor/acceptor (D/A) interfacial area in the active layer that facilitates exciton dissociation. The reduced effective interfacial area between the photoactive layer and the ZnO interlayer with decreased ZnO surface roughness leads to an observed improvement in both fill factor and open circuit voltage, which is ascribed to a reduced concentration of traps at the interface between the ZnO interlayer and the active layer.

Solution-processed zinc oxide nanoparticles as interlayer materials for inverted organic solar cells

This paper describes inverted bulk heterojunction organic solar cells featuring solution-processed zinc oxide nanoparticles (ZnO NPs) as an electron extraction layer, prepared at relatively low annealing temperatures (≤150°C). A solution of ZnO NPs (average size: 25nm) was prepared using a wet grinding method. When the ZnO interlayer was present in the solar cell, the vertical phase separation of the active layers prepared with and without solvent annealing exhibited similar gradient concentrations and, therefore, similar photocurrent generation, both of which were superior to those of conventional devices incorporating a poly(3,4-ethylenedioxythiophene):poly(styrene sulfonic acid) (PEDOT:PSS) hole extraction layer. We attribute this vertical phase separation to the similar surface energies of the fullerene derivative and the ZnO interlayer. Under simulated air mass (AM) 1.5G illumination at 100mWcm−2, the power conversion efficiency of the optimized device was approximately 4%.

Synthesis of hollow Fe3O4 at ZnO at anatase TiO2 core–shell structured spheres

Hollow Fe3O4 at ZnO at anatase TiO2 core–shell structured spheres have been successfully synthesized through a simple two-step sol–gel method and the synthesis process is illustrated as an explicit schematic diagram. Surfactant cetyltrimethylammonium bromide was employed to realize the mesoporous anatase TiO2 shell on the surface of Fe3O4 at ZnO composite spheres. Electron microscopy examinations indicate that the composite core–shell structured hollow spheres have a homogeneous ZnO interlayer and an anatase TiO2 shell outside the ZnO layer, both of which have a thickness of about 20nm. The magnetization hysteresis curves of the samples show that the core–shell structured composites have a magnetic saturation value of 41.5emu/g, suggesting that the obtained product can be separated easily from reaction system and put into recyclable applications.

Controllable synthesis of novel sandwiched polyaniline/ZnO/polyaniline free‐standing nanocomposite films

AbstractControllable synthesis of novel sandwiched polyaniline (PANI)/ZnO/PANI free‐standing nanocomposite films is reported via spin coating of ZnO quantum‐dot interlayer on PANI base layer and then PANI surface layer on the ZnO interlayer. The thickness of the ZnO interlayer and the PANI surface layer can be easily controlled by adjusting spin time and spin speed, respectively. The effects of the ZnO interlayer thickness and the PANI surface layer thickness are examined in detail on the photoluminescence (PL) property. It is worth noting that coverage of the PANI surface layer on the ZnO interlayer can not only lead to great enhancement in the PL property but also to a maximum PL intensity at a medium PANI surface layer thickness. This maximum PL property is caused by the combined ZnO/PANI carrier transportation and PANI shielding effects. In addition, the nanocomposite films show reasonably good conductivity. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012

Plasmonic effects in amorphous silicon thin film solar cells with metal back contacts

Plasmonic effects in amorphous silicon thin film solar cells with randomly textured metal back contact were investigated experimentally and numerically. The influence of different metal back contacts with and without ZnO interlayer was studied and losses in the individual layers of the solar cell were quantified. The amorphous silicon thin film solar cells were prepared on randomly textured substrates using large area production equipment and exhibit conversion efficiencies approaching 10%. The optical wave propagation within the solar cells was studied by Finite Difference Time Domain simulations. The quantum efficiency of solar cells with and without ZnO interlayer was simulated and the interplay between the reflection, quantum efficiency and absorption in the back contact will be discussed.

Effect of a compact ZnO interlayer on the performance of ZnO-based dye-sensitized solar cells

ZnO is a promising material for application in dye-sensitized solar cells, related to its attractive electrical properties and the facile preparation of nanomaterials, with excellent control over the structure and morphology. In this work ZnO-based dye-sensitized solar cells were prepared, and the effect of the presence of a compact ZnO interlayer between the transparent conducting oxide (TCO) electrode and the nanostructured, mesoporous ZnO film on the performance of the solar cell is reported. The compact interlayer was deposited using planar rf magnetron sputtering, and the ZnO nanomaterial was prepared by forced hydrolysis from zinc acetate in ethanol solution. The presence of the compact interlayer has a positive effect on the overall characteristics of the solar cell and decreases the recombination rate from the TCO substrate, resulting in a higher open circuit voltage under low light conditions. The best efficiency of non-optimized solar cells at 1 sun was 4.0%.

Influence of ZnO interlayer on the performance of inverted organic photovoltaic device

Inverted organic photovoltaic devices with a structure of fluorine tin oxide (FTO)/ZnO/poly(3-hexylthiophene) (P3HT):[6,6]-phenyl C 61 butyric acid methyl ester (PCBM)/Ag were fabricated, in which ZnO interlayer serves as an electron selective layer. The ZnO interlayer includes three different nanostructures: polycrystalline seed layer, polycrystalline seed layer/loose nanopillars and polycrystalline seed layer/dense nanopillars. The influences of the different ZnO interlayers on the device performance were investigated. It is concluded that the polycrystalline seed layer/loose nanopillars offer more interfacial area with the P3HT:PCBM blends and acts as a continuous conducting path to the cathode. Our results demonstrate that effective infiltration of the blends into the ZnO nanopillars is critical for optimizing the device performance.

Fabrication of the p-MgZnO/ZnO/n-MgZnO double-heterojunction by MOCVD

The p-MgZnO/i-ZnO/n-MgZnO double-heterojuntion was fabricated on GaAs (100) substrate by photon-assistant metal-organic chemical vapor deposition. We can found an obvious ultraviolet peak in the electroluminescence spectra and the causation has been discussed. The effects of the thickness of ZnO interlayer on the junctions properties was also analyzed. The conclusion indicated the intensity of the UV peak would increase by decreasing the thickness of ZnO interlayer. The thickness of ZnO layer had important impact on the optical qualities of the double-heterojunction.

Study on the p-MgZnO/i-ZnO/n-MgZnO light-emitting diode fabricated by MOCVD

A p-MgZnO/i-ZnO/n-MgZnO light-emitting diode was fabricated on a GaAs substrate by metal–organic chemical vapour deposition. The I–V curve of the device exhibited typical rectifying behaviour of the p–i–n diode and the forward turn-on voltage was about 7 V. An obvious ultraviolet peak can be observed in the electroluminescence spectrum corresponding to the radiative recombination of carriers. The dependences of the characteristics on the thickness of the ZnO interlayer were also studied. The results showed that the intensity of the UV peak increased as the thickness of the ZnO layer decreased. A clear blue shift can also be observed at the same time. The thickness of the ZnO layer had an important effect on the optical qualities of the device.

Observation of interfacial reactions and recrystallization of extrinsic phases in epitaxial grown ZnO/GaAs heterostructures

Thermal-induced interfacial reactions and recrystallization of extrinsic phases in ZnO/GaAs heterostructures were observed by using high-resolution X-ray diffraction and transmission electron microscopy. A uniform Zn 3As 2 interlayer and a defected ZnO interlayer (i.e. embedded with nanoscale ZnGa 2O 4 domains) are formed, adjacent to each other along the growth direction, at elevated temperatures. The anomalous distribution of Zn and Ga elements over the two interlayers as confirmed by energy-dispersive spectroscopy conflicts with atoms interdiffusion driven only by concentration gradient. Chemical reactions between the diffused cations and the steady anions may accelerate the Ga/Zn atoms interdiffusion and result in the observed structures.

Inverted bulk-heterojunction organic photovoltaic device using a solution-derived ZnO underlayer

Inverted organic photovoltaic devices based on a blend of poly(3-hexylthiophene) and a fullerene have been developed by inserting a solution-processed ZnO interlayer between the indium tin oxide (ITO) electrode and the active layer using Ag as a hole-collecting back contact. Efficient electron extraction through the ZnO and hole extraction through the Ag, with minimal loss in open-circuit potential, is observed with a certified power conversion efficiency of 2.58%. The inverted architecture removes the need for the use of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) as an ITO modifier and for the use of a low-work-function metal as the back contact in the device.

The AC Conductivity and Dielectric Constant of (006) Textured LiNbO3 Films

c-axis oriented LiNbO3 films are grown by pulsed laser deposition technique on the Si substrate using a transparent conducting Al doped ZnO inter-layer. Film quality has been examined by means of X-ray diffraction and atomic force microscopy. Dielectric properties of the c-axis oriented LiNbO3 film as a function of frequency (0.1 KHz to 1.0 MHz) and temperature (100 to 450 K) in metal-insulator-metal configuration are investigated. Large frequency dispersion was observed in the dielectric constant at higher temperatures (> 300 K), whereas below room temperature a weak frequency dispersion and small temperature dependence was found. The ac conductivity and dielectric data are in good agreement with the reported results on LiNbO3 single crystals. Communicated by Prof. Amar S. Bhalla