Enhanced critical current densities in MgB2 by mixing relatively impure boron powders.

Polycrystalline MgB2 samples were prepared from 99.98% purity Mg powder and different mixtures of relatively impure boron (99% pure crystalline boron and 95–97% amorphous boron) precursor powders. At both 6 and 20 K, for the mixed boron samples a doubling in Jc was observed over the highest values for single precursor samples. It is shown that the enhanced Jc results from the mixing effect of using different reaction rates of the different boron precursor powders. The work represents a cost-effective means of significantly improving current carrying Performance in MgB2 conductors

The critical current density of polycrystalline MgB2 prepared by using boron mixture

In this study, boron powders with varying purity and form were mixed in different proportion to serve as precursors for reaction with Mg forming polycrystalline MgB2 bulks. The inductively measured superconducting transition temperature, Tc and the critical current density, J c were compared to that of samples prepared from the respective single boron. Overall, Tc remains largely unchanged for all samples. It was found that Jc at 6 K and 20 K did not degrade significantly up to 4.6 T as a result of adding impure boron as much as 10 wt.% indicating comparable Jc can be obtained without dependence of use of expensive high purity boron powder alone. The systematic decrease of Jc with increasing impure boron additions shows that a compromise between desired and cost reduction can be made by varying the boron powder proportion. Finally, samples prepared from the mixture of both impure crystalline and amorphous borons even show enhanced Jc up to 3 T at 20 K. The increase in Jc correlates with the retention of strain level in these samples probably resulted from the more similar reaction rate of the respective borons

High Yield Transfer of Clean Large-Area Epitaxial Oxide Thin Films

Highlights: A new way to achieve high yield and large area oxide thin film transfer is developed. Three different film compositions are demonstrated: SrRuO3, CeO2, and CeO2/STO nanocomposite films. Cracks, wrinkles, and damages are prevented by the new transfer method. They are commonly introduced by conventional transfer processes. Vertically aligned nanocomposite (VAN) structures can further improve the transfer yield. Possible mechanisms related to increased fracture toughness are proposed. We have opened up a route to large-scale oxide thin-film-based electronic device applications

Tuning of defects in ZnO nanorod arrays used in bulk heterojunction solar cells.

With particular focus on bulk heterojunction solar cells incorporating ZnO nanorods, we study how different annealing environments (air or Zn environment) and temperatures impact on the photoluminescence response. Our work gives new insight into the complex defect landscape in ZnO, and it also shows how the different defect types can be manipulated. We have determined the emission wavelengths for the two main defects which make up the visible band, the oxygen vacancy emission wavelength at approximately 530 nm and the zinc vacancy emission wavelength at approximately 630 nm. The precise nature of the defect landscape in the bulk of the nanorods is found to be unimportant to photovoltaic cell performance although the surface structure is more critical. Annealing of the nanorods is optimum at 300°C as this is a sufficiently high temperature to decompose Zn(OH)2 formed at the surface of the nanorods during electrodeposition and sufficiently low to prevent ITO degradation.RIGHTS : This article is licensed under the BioMed Central licence at http://www.biomedcentral.com/about/license which is similar to the 'Creative Commons Attribution Licence'. In brief you may : copy, distribute, and display the work; make derivative works; or make commercial use of the work - under the following conditions: the original author must be given credit; for any reuse or distribution, it must be made clear to others what the license terms of this work are

Research Update: Doping ZnO and TiO2 for solar cells

© Author(s). This article is distributed under a Creative Commons Attribution (CC BY) License.ZnO and TiO2 are two of the most commonly used n-type metal oxide semiconductors in new generation solar cells due to their abundance, low-cost, and stability. ZnO and TiO2 can be used as active layers, photoanodes, buffer layers, transparent conducting oxides, hole-blocking layers, and intermediate layers. Doping is essential to tailor the materials properties for each application. The dopants used and their impact in solar cells are reviewed. In addition, the advantages, disadvantages, and commercial potential of the various fabrication methods of these oxides are presented.Rutherford Foundation of New ZealandCambridge Commonwealth TrustGirton College CambridgeERC Advanced Investigator GrantNovox [ERC-2009-adG247276

Improved Heterojunction Quality in Cu2O-based Solar Cells Through the Optimization of Atmospheric Pressure Spatial Atomic Layer Deposited Zn1-xMgxO.

Atmospheric pressure spatial atomic layer deposition (AP-SALD) was used to deposit n-type ZnO and Zn1-xMgxO thin films onto p-type thermally oxidized Cu2O substrates outside vacuum at low temperature. The performance of photovoltaic devices featuring atmospherically fabricated ZnO/Cu2O heterojunction was dependent on the conditions of AP-SALD film deposition, namely, the substrate temperature and deposition time, as well as on the Cu2O substrate exposure to oxidizing agents prior to and during the ZnO deposition. Superficial Cu2O to CuO oxidation was identified as a limiting factor to heterojunction quality due to recombination at the ZnO/Cu2O interface. Optimization of AP-SALD conditions as well as keeping Cu2O away from air and moisture in order to minimize Cu2O surface oxidation led to improved device performance. A three-fold increase in the open-circuit voltage (up to 0.65 V) and a two-fold increase in the short-circuit current density produced solar cells with a record 2.2% power conversion efficiency (PCE). This PCE is the highest reported for a Zn1-xMgxO/Cu2O heterojunction formed outside vacuum, which highlights atmospheric pressure spatial ALD as a promising technique for inexpensive and scalable fabrication of Cu2O-based photovoltaics.The authors acknowledge the support of the Cambridge Overseas and Commonwealth Trust, the Rutherford Foundation of New Zealand, Girton College Cambridge. This work has been funded by ERC Advanced Investigator Grant, Novox, ERC-2009-adG247276 and by the EPSRC (under RGS3717)

Accurate determination of interface trap state parameters by admittance spectroscopy in the presence of a Schottky barrier contact: Application to ZnO-based solar cells

This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. The following article appeared in Marin, A. T., Musselman, K. P., & MacManus-Driscoll, J. L. (2013). Accurate determination of interface trap state parameters by admittance spectroscopy in the presence of a Schottky barrier contact: Application to ZnO-based solar cells. Journal of Applied Physics, 113(14), 144502 and may be found at https://doi.org/10.1063/1.4799633This work shows that when a Schottky barrier is present in a photovoltaic device, such as in a device with an ITO/ZnO contact, equivalent circuit analysis must be performed with admittance spectroscopy to accurately determine the pn junction interface recombination parameters (i.e., capture cross section and density of trap states). Without equivalent circuit analysis, a Schottky barrier can produce an error of similar to 4-orders of magnitude in the capture cross section and similar to 50% error in the measured density of trap states. Using a solution processed ZnO/Cu2O photovoltaic test system, we apply our analysis to clearly separate the contributions of interface states at the pn junction from the Schottky barrier at the ITO/ZnO contact so that the interface state recombination parameters can be accurately characterized. This work is widely applicable to the multitude of photovoltaic devices, which use ZnO adjacent to ITO.International Copper AssociationERC for the Advanced Investigator Grant, Novox [ERC-2009-adG 247276]Gates Cambridge TrustGirton College (Cambridge

Tailoring physical functionalities of complex oxides by vertically aligned nanocomposite thin-film design

Abstract: Self-assembled nanocomposite thin films couple two materials into a single film, typically, in the form of vertically aligned nanopillars embedded in a matrix film. High-density vertical heterointerfaces provide a great platform for engineering new physical properties and novel multifunctionalities, as well as for nanoscale device integration. Tremendous research efforts have been devoted to developing different nanocomposite systems. In this article, we summarize recent progress on vertically aligned nanocomposite thin films for enhanced functionalities such as ferroelectricity, tunable magnetoresistance, multiferroicity, dielectricity, magnetic anisotropy, perpendicular exchange bias, novel electrical/ionic properties, interfacial conduction, and resistive switching. Using specific examples, we discuss how and why the fundamental physical properties can be significantly tuned/improved in vertically aligned nanocomposites. Finally, we propose future research directions to achieve further enhanced performance as well as practical devices