Electrodeposited NiO anode interlayers: Enhancement of the charge carrier selectivity in organic solar cells

Nickel oxide (NiO) thin films prepared by cathodic electrodeposition exhibit superior electrical performace than PEDOT:PSS when used as anode interlayers of bulk-heterojunction solar cells. Devices incorporating 30 nm-thick NiO films firstly annealed at 320 °C in air and posteriorly treated with UV-O3 reach power conversion efficiencies comparable to that obtained for PEDOT:PSS-based cells. NiO interlayers enhance contact selectivity by simulataneously increasing shunt resistance (lower leakage current related to electron-blocking ability), and reducing hole-extraction resistance. Carrier selectivity is quantified from the resistance components associated with the impedance response of the anode contacts. The versatile electrodeposition technique of NiO interlayers permits avoiding PEDOT:PSS use as it presents disadvantages related to its acid character and hygroscopic nature

A practical perspective on the potential of rechargeable Mg batteries

Emerging energy storage systems based on abundant and cost-effective materials are key to overcome the global energy and climate crisis of the 21st century. Rechargeable Magnesium Batteries (RMB), based on Earth-abundant magnesium, can provide a cheap and environmentally responsible alternative to the benchmark Li-ion technology, especially for large energy storage applications. Currently, RMB technology is the subject of intense research efforts at laboratory scale. However, these emerging approaches must be placed in a real-world perspective to ensure that they satisfy key technological requirements. In an attempt to bridge the gap between laboratory advancements and industrial development demands, herein, we report the first non-aqueous multilayer RMB pouch cell prototypes and propose a roadmap for a new advanced RMB chemistry. Through this work, we aim to show the great unrealized potential of RMBs.This work was funded by European Union's Horizon 2020 research and innovation program under the FET Proactive call with grant agreement no 824066 via the “E-MAGIC” project

A practical perspective on the potential of rechargeable Mg batteries

Emerging energy storage systems based on abundant and cost-effective materials are key to overcome the global energy and climate crisis of the 21st century. Rechargeable Magnesium Batteries (RMB), based on Earth-abundant magnesium, can provide a cheap and environmentally responsible alternative to the benchmark Li-ion technology, especially for large energy storage applications. Currently, RMB technology is the subject of intense research efforts at laboratory scale. However, these emerging approaches must be placed in a real-world perspective to ensure that they satisfy key technological requirements. In an attempt to bridge the gap between laboratory advancements and industrial development demands, herein, we report the first non-aqueous multilayer RMB pouch cell prototypes and propose a roadmap for a new advanced RMB chemistry. Through this work, we aim to show the great unrealized potential of RMBs

Development of ZnO nanowire based CdTe thin film solar cells

This work reports on the development of CdTe thin film solar cells grown on ZnO nanowire arrays. The focus was placed on utilising ZnO nanowire arrays as a replacement to the conventional ZnO thin film buffer layer, thereby requiring minimal alteration to the existing solar cell structure. Incorporation of nanowires was found to alter subsequent film growth and processing, with the nanowire dimensions changing device performance significantly. Shorter, ~100 nm, wires were found to produce particularly low device performance of <0.5% whilst longer wires in the range 250–2000 nm were able to produce more functional cells. Working devices of up to 9.5% efficiency were achieved through the production of “embedded tip” nanowire solar cells. Variation of the nanowires length demonstrated that the nanowires were involved in carrier recombination and that this may be the performance limiting factor

Modeling and characterization of extremely thin absorber (eta) solar cells based on ZnO nanowires

Extremely thin absorber (eta)-solar cells based on ZnO nanowires sensitized with a thin layer of CdSe have been prepared, using CuSCN as hole transporting material. Samples with significantly different photovoltaic performance have been analyzed and a general model of their behavior was obtained. We have used impedance spectroscopy to model the device discriminating the series resistance, the role of the hole conducting material CuSCN, and the interface process. Correlating the impedance analysis with the microstructural properties of the solar cell interfaces, a good description of the solar cell performance is obtained. The use of thick CdSe layers leads to high recombination resistances, increasing the open circuit voltage of the devices. However, there is an increase of the internal recombination in thick light absorbing layers that also inhibit a good penetration of CuSCN, reducing the photocurrent. The model will play an important role on the optimization of these devices. This analysis could have important implications for the modeling and optimization of all-solid devices using a sensitizing configuration

Effect of different photoanode nanostructures on the initial charge separation and electron injection process in dye sensitized solar cells: a photophysical study with indoline dyes

Ultrafast and fast charge separation processes were investigated for complete cells based on several ZnO-based photoanode nanostructures and standard TiO2 nanoparticle layers sensitized with the indoline dye coded D358. Different ZnO morphologies (nanoparticles, nanowires, mesoporous), synthesis methods (hydrothermal, gas-phase, electrodeposition in aqueous media and ionic liquid media) and coatings (ZnO -ZnO core-shell, ZnO-TiO2 core-shell) were measured by transient absorption techniques in the time scale from 100 fs to 100 ps and in the visible and near-infrared spectral range. All of ZnO cells show worse electron injection yields with respect to those with standard TiO2 material. Lower refractive index of ZnO than that of TiO2 is suggested to be an additional factor, not considered so far, that can decrease the performance of ZnO-based solar cells. Evidence of the participation of the excited charge transfer state of the dye in the charge separation process is provided here. The lifetime of this state in fully working devices extends from several ps to several tens of ps, which is much longer than the typically postulated electron injection times in all-organic dye-sensitized solar cells. The results here provided, comprising a wide variety of morphologies and preparation methods, point to the universality of the poor performance of ZnO as photoanode material with respect to standard TiO2. (C) 2015 Elsevier B.V. All rights reserved

Multifunctional carbon nanotube composite fibers: Properties and electronic textile applications

Work presented at the 25th International Conference on Diamond and Carbon Materials, 7th-11th september 2014, Madrid (Spain)Remarkable progress in the fabrication of carbon nanotube composite fibers has resulted through the development of the wet-spinning technique pioneered by Vigolo et al. [1] This process implies the fabrication of gel fibers as a result of the collapse of surfactant-stabilized carbon nanotube dispersions when injected into a coagulation bath. When dried, those gel fibers become solid fibers with high carbon nanotube contents (³ 50 wt.%), significantly higher than those achieved by other fiber spinning technologies, such as melt-spinning or electrospinning. We here report how this wet-spinning method provides carbon nanotube composite fibers with tunable properties, which mainly depend on the composition of the coagulation bath used. Polymers including polyvinyl alcohol (PVA) [2-5] and polyethylenimine (PEI) [6] have been here investigated as coagulants.[7] Remarkable transport-, supercapacitor- and electrochemical actuation properties are demonstrated for these coagulation wet-spun fibers, that can be woven into fabrics and therefore offer promise for a variety of electronic textile applications [2-4].This work has been funded by the Fundación Domingo Martínez (Ayuda a la Investigación 2013)

Nanophotoactivity of Porphyrin Functionalized Polycrystalline ZnO Films

Kelvin probe force microscopy in darkness and under illumination is reported to provide nanoscale-resolved surface photovoltage maps of hybrid materials. In particular, nanoscale charge injection and charge recombination mechanisms occurring in ZnO polycrystalline surfaces functionalized with Protoporphyrin IX (H2PPIX) are analyzed. Local surface potential and surface photovoltage maps not only reveal that upon molecular adsorption the bare ZnO work function increases, but also they allow study of its local dependence. Nanometer-sized regions not correlated with apparent topographic features were identified, presenting values significantly different from the average work function. Depending on the region, the response to the light excitation is different, distinguishing two relaxation processes, one faster than the other. This behavior can be explained in terms of electrons trapped closed to the molecule–semiconductor interface or electrons pushed into the ZnO bulk, respectively. Moreover, the origin of these differences is correlated with the H2PPIX–ZnO bonding and molecules configuration and aggregation. The chenodeoxycholic acid (CDCA) coadsorption leads to a more homogeneous surface potential distribution, confirming the antiaggregate effect of this additive, while the surface photovoltage is mostly dominated by the slow relaxation component. This work reveals the complexity of real device architectures with ill-defined surfaces even in a relatively simple system with only one type of dye molecule and hightlights the importance of nanoscale characterization with appropriate tools

One-step wet chemical deposition of NiO from the electrochemical reduction of nitrates in ionic liquid based electrolytes

Aprotic PYR14TFSI (1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)) ionic liquid served to develop a new electrochemical route for one-step deposition of NiO from PYR14NO3 reduction (1-butyl-1-methylpyrrolidinium nitrate) in a Ni(TFSI)2 (Nickel (II) bis(trifluoromethanesulfonyl)imide) containing electrolyte. The high solubility of the novel PYR14NO3 salt in PYR14TFSI (>0.1 M) in comparison with other oxygenated precursors such as oxygen gas, NaNO 3 or KNO3 (i.e. 10-15 mM) allows the formulation of a broad variety of electrolytes which opens wide possibilities to tune the physico-chemical properties of NiO films (e.g. morphology: from flat to nanostructured films). Furthermore, electrochemical deposition in an electrolyte containing low water concentration (>30 ppm by Karl Fisher titration) served to demonstrate that only a small amount of moisture dramatically affects the electrochemical reduction of NO3 -, resulting in OH - generation close to the cathode and subsequent NiO(OH)/Ni(OH) 2 deposition, as proved by X-ray diffraction and X-ray photoelectron spectroscopy. This finding highlights the importance of aprotic ionic liquids in developing a general electrochemical route for metal oxide deposition without the formation of metal hydroxide species, thus avoiding the requirement for post-deposition annealing treatments. The versatility of the present deposition route as well as its impact in (opto)electronic devices was pointed out by the successful preparation of nanostructured n-p ZnO/NiO heterojunctions exhibiting rectifying current-voltage characteristics. © 2013 Elsevier Ltd.Financial support by the European Union (ORION CP-IP 229036-2), Spanish Ministerio de Economia y Competitividad (HOPE CSD2007-0007, Consolider-Ingenio 2010, MAT2010-21156-C03-03, PIB2010US-00652) and Basque Government (IT-621-13) are gratefully acknowledged. R.T-Z. acknowledges the support of the Program “Ramon y Cajal” of the MICINN.Peer Reviewe