Electrochemical removal of anodic aluminium oxide templates for the production of phase-pure cuprous oxide nanorods for antimicrobial surfaces.

Antimicrobial surfaces are ones that incapacitate or kill pathogens landing on them, which could allow for self-sanitising surfaces for hospitals or implants, ensuring healthier stays and procedures. Cuprous compounds such as Cu2O are especially effective at incapacitating both viruses and bacteria, and nanorod arrays have been shown to prevent the adhesion of pathogens and mechanically deform bacteria to the point that their cell walls rupture. A Cu2O nanorod array should therefore allow for the exploitation of both of these effects. In the present work, an electrochemical method is introduced, where Cu2O nanorods formed in a substrate-supported anodic aluminium oxide (AAO) template are held at a stable electrochemical potential throughout the removal of the AAO template. This avoids the partial reduction of the nanorods from Cu2O to Cu that was observed during chemical removal of the template, which was attributed to the presence of residual aluminium from the template fabrication process that reacts with the etchant and lowers the electrochemical potential of the nanorods to a value that favours reduction. Using the electrochemical removal method, the reliable production of phase-pure, free-standing, crystalline Cu2O nanorod arrays on ITO/glass substrates is demonstrated. This simple method is compatible with nanorod arrays of any size

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

Maintaining surface-phase purity is key to efficient open air fabricated cuprous oxide solar cells

This is the final published version. It first appeared at http://scitation.aip.org/content/aip/journal/aplmater/3/2/10.1063/1.4913442.Electrochemically deposited Cu 2O solar cells are receiving growing attention owing to a recent doubling in efficiency. This was enabled by the controlled chemical environment used in depositing doped ZnO layers by atomic layer deposition, which is not well suited to large-scale industrial production. While open air fabrication with atmospheric pressure spatial atomic layer deposition overcomes this limitation, we find that this approach is limited by an inability to remove the detrimental CuO layer that forms on the Cu 2O surface. Herein, we propose strategies for achieving efficiencies in atmospherically processed cells that are equivalent to the high values achieved in vacuum processed cells.The authors acknowledge funding from the Cambridge Commonwealth, European and International Trusts (R.L.Z.H. and Y.I.), Rutherford Foundation of New Zealand (R.L.Z.H.), an NSF Graduate Research Fellowship (R.E.B.), EPSRC of the UK (S.H.), University of Cambridge EPSRC Centre for Doctoral Training in Nanoscience (S.H.), Girton College Cambridge (K.P.M.), an NSF CAREER Award ECCS-1150878 (T.B.), the National Research Foundation Singapore through the Singapore Massachusetts Institute of Technology Alliance for Research and Technology’s Low Energy Electronics Systems research program (T.B.), and an ERC Advanced Investigator Grant, Novox, ERC-2009-adG247276 (J.L.D.)

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

Resistive Switching Memory of TiO2 Nanowire Networks Grown on Ti Foil by a Single Hydrothermal Method

The resistive switching characteristics of TiO2 nanowire networks directly grown on Ti foil by a single-step hydrothermal technique are discussed in this paper. The Ti foil serves as the supply of Ti atoms for growth of the TiO2 nanowires, making the preparation straightforward. It also acts as a bottom electrode for the device. A top Al electrode was fabricated by e-beam evaporation process. The Al/TiO2 nanowire networks/Ti device fabricated in this way displayed a highly repeatable and electroforming-free bipolar resistive behavior with retention for more than 10(4) s and an OFF/ON ratio of approximately 70. The switching mechanism of this Al/TiO2 nanowire networks/Ti device is suggested to arise from the migration of oxygen vacancies under applied electric field. This provides a facile way to obtain metal oxide nanowire-based ReRAM device in the future.Natural Sciences and Engineering Research Council (NSERC) of CanadaState Scholarship Fund of China [201506160061

Resonant energy transfer of triplet excitons from pentacene to PbSe nanocrystals.

The efficient transfer of energy between organic and inorganic semiconductors is a widely sought after property, but has so far been limited to the transfer of spin-singlet excitons. Here we report efficient resonant-energy transfer of molecular spin-triplet excitons from organic semiconductors to inorganic semiconductors. We use ultrafast optical absorption spectroscopy to track the dynamics of triplets, generated in pentacene through singlet exciton fission, at the interface with lead selenide (PbSe) nanocrystals. We show that triplets transfer to PbSe rapidly (<1 ps) and efficiently, with 1.9 triplets transferred for every photon absorbed in pentacene, but only when the bandgap of the nanocrystals is close to resonance (±0.2 eV) with the triplet energy. Following triplet transfer, the excitation can undergo either charge separation, allowing photovoltaic operation, or radiative recombination in the nanocrystal, enabling luminescent harvesting of triplet exciton energy in light-emitting structures.This is the author's accepted manuscript and will be under embargo until the 5th of April 2015. The final version is published by NPG in Nature Materials here: http://www.nature.com/nmat/journal/v13/n11/full/nmat4093.html

The application of localized surface plasmons resonance in Ag nanoparticles assisted Si chemical etching

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 Ding, R., Dai, H., Li, M., Huang, J., Li, Y., Trevor, M., & Musselman, K. P. (2014). The application of localized surface plasmons resonance in Ag nanoparticles assisted Si chemical etching. Applied Physics Letters, 104(1), 011602 and may be found at https://doi.org/10.1063/1.4855615Localized surface plasmons excited by Ag nanoparticles are introduced in the chemical etching process of silicon. A special crateriform structure with gradually varying radius is achieved by the surface electromagnetic field enhancement effect of localized surface plasmons resonance (LSPR). Theoretical analysis demonstrates that the formation kinetics of the crateriform structures conforms to the local electromagnetic field enhancement and forward scattering induced by LSPR. The LSPR assisted photocatalytic etching offers a potential approach for the preparation of the surface microstructures used in optoelectronic devices.National Natural Science Foundation of China [91333122, 51372082, 51172069, 50972032, 61204064, 51202067]Ph.D. Programs Foundation of Ministry of Education of China [20130036110012, 20110036110006]Fundamental Research Funds for the Central Universities [11ZG02

Fabrication of ZnO/Cu2O heterojunctions in atmospheric conditions: Improved interface quality and solar cell performance

Zn1−xMgxO/Cu2O heterojunctions were successfully fabricated in open-air at low temperatures via atmospheric atomic layer deposition of Zn1−xMgxO on thermally oxidized cuprous oxide. Solar cells employing these heterojunctions demonstrated a power conversion efficiency exceeding 2.2% and an open-circuit voltage of 0.65V. Surface oxidation of Cu2O to CuO prior to and during Zn1−xMgxO deposition was identified as the limiting factor to obtaining a high quality heterojunction interface. Optimization of deposition conditions to minimize Cu2O surface oxidation led to improved device performance, tripling the open-circuit voltage and doubling the short-circuit current density. These values are the highest reported for a ZnO/Cu2O interface formed in air, and highlight atmospheric ALD as a promising technique for inexpensive and scalable fabrication of ZnO/Cu2O heterojunctions.Cuprous oxideSpatial atmospheric ALDZnO/Cu2O heterojunctionInorganic solar cel

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.Cambridge Overseas and Commonwealth Trust, the Rutherford Foundation of New Zealand, Girton College CambridgeERC Advanced Investigator Grant, Novox [ERC-2009-adG247276]EPSRC [RGS3717