Bipolar Charge Transport in Poly(3-hexyl thiophene)/Methanofullerene Blends: A Ratio Dependent Study

We investigated the charge carrier mobility in pristine poly(3-hexyl thiophene-2,5-diyl) (P3HT):[6,6]-phenyl-C61 butyric acid methyl ester (PCBM) blend devices by applying the time resolved photoconductivity experiment in dependence on the donor:acceptor ratio. We observe a bipolar transport in all studied samples ranging from pure polymer to polymer:fullerene with 90% PCBM content. For the ratios P3HT:PCBM 1:4 and 1:1 we observe two transit times in the electron current transients, as well as hole double transients for P3HT:PCBM 1:2. We find high hole and electron mobilities in the order of 10^(-3) - 10^(-2) cm^2/Vs for a concentration of 90% PCBM in the blend.Comment: 3 pages, 1 table, 2 figures, minor corrections include

Charge Carrier Extraction by Linearly Increasing Voltage:Analytic framework and ambipolar transients

Up to now the basic theoretical description of charge extraction by linearly increasing voltage (CELIV) is solved for a low conductivity approximation only. Here we present the full analytical solution, thus generalize the theoretical framework for this method. We compare the analytical solution and the approximated theory, showing that especially for typical organic solar cell materials the latter approach has a very limited validity. Photo-CELIV measurements on poly(3-hexyl thiophene-2,5-diyl):[6,6]-phenyl-C61 butyric acid methyl ester based solar cells were then evaluated by fitting the current transients to the analytical solution. We found that the fit results are in a very good agreement with the experimental observations, if ambipolar transport is taken into account, the origin of which we will discuss. Furthermore we present parametric equations for the mobility and the charge carrier density, which can be applied over the entire experimental range of parameters.Comment: 8 pages, 5 figure

Direct observation of lithium metal dendrites with ceramic solid electrolyte

Dendrite formation, which could cause a battery short circuit, occurs in batteries that contain lithium metal anodes. In order to suppress dendrite growth, the use of electrolytes with a high shear modulus is suggested as an ionic conductive separator in batteries. One promising candidate for this application is Li7La3Zr2O12 (LLZO) because it has excellent mechanical properties and chemical stability. In this work, in situ scanning electron microscopy (SEM) technique was employed to monitor the interface behavior between lithium metal and LLZO electrolyte during cycling with pressure. Using the obtained SEM images, videos were created that show the inhomogeneous dissolution and deposition of lithium, which induce dendrite growth. The energy dispersive spectroscopy analyses of dendrites indicate the presence of Li, C, and O elements. Moreover, the cross-section mapping comparison of the LLZO shows the inhomogeneous distribution of La, Zr, and C after cycling that was caused by lithium loss near the Li electrode and possible side reactions. This work demonstrates the morphological and chemical evolution that occurs during cycling in a symmetrical Li–Li cell that contains LLZO. Although the superior mechanical properties of LLZO make it an excellent electrolyte candidate for batteries, the further improvement of the electrochemical stabilization of the garnet–lithium metal interface is suggested

Effect of doping-- and field--induced charge carrier density on the electron transport in nanocrystalline ZnO

Charge transport properties of thin films of sol--gel processed undoped and Al-doped zinc oxide nanoparticles with variable doping level between 0.8 at% and 10 at% were investigated. The X-ray diffraction studies revealed a decrease of the average crystallite sizes in highly doped samples. We provide estimates of the conductivity and the resulting charge carrier densities with respect to the doping level. The increase of charge carrier density due to extrinsic doping were compared to the accumulation of charge carriers in field effect transistor structures. This allowed to assess the scattering effects due to extrinsic doping on the electron mobility. The latter decreases from 4.6*10^-3 cm^2/Vs to 4.5*10^-4 cm^2/Vs with increasing doping density. In contrast, the accumulation leads to an increasing mobility up to 1.5*10^-2 cm^2/Vs. The potential barrier heights related to grain boundaries between the crystallites were derived from temperature dependent mobility measurements. The extrinsic doping initially leads to a grain boundary barrier height lowering, followed by an increase due to doping-induced structural defects. We conclude that the conductivity of sol--gel processed nanocrystalline ZnO:Al is governed by an interplay of the enhanced charge carrier density and the doping-induced charge carrier scattering effects, achieving a maximum at 0.8 at% in our case.Comment: 8 pages, 7 figure

Rechargeable Batteries of the Future—The State of the Art from a BATTERY 2030+ Perspective

The development of new batteries has historically been achieved through discovery and development cycles based on the intuition of the researcher, followed by experimental trial and error—often helped along by serendipitous breakthroughs. Meanwhile, it is evident that new strategies are needed to master the ever-growing complexity in the development of battery systems, and to fast-track the transfer of findings from the laboratory into commercially viable products. This review gives an overview over the future needs and the current state-of-the art of five research pillars of the European Large-Scale Research Initiative BATTERY 2030+, namely 1) Battery Interface Genome in combination with a Materials Acceleration Platform (BIG-MAP), progress toward the development of 2) self-healing battery materials, and methods for operando, 3) sensing to monitor battery health. These subjects are complemented by an overview over current and up-coming strategies to optimize 4) manufacturability of batteries and efforts toward development of a circular battery economy through implementation of 5) recyclability aspects in the design of the battery

A Roadmap for Transforming Research to Invent the Batteries of the Future Designed within the European Large Scale Research Initiative BATTERY 2030+

This roadmap presents the transformational research ideas proposed by “BATTERY 2030+,” the European large-scale research initiative for future battery chemistries. A “chemistry-neutral” roadmap to advance battery research, particularly at low technology readiness levels, is outlined, with a time horizon of more than ten years. The roadmap is centered around six themes: 1) accelerated materials discovery platform, 2) battery interface genome, with the integration of smart functionalities such as 3) sensing and 4) self-healing processes. Beyond chemistry related aspects also include crosscutting research regarding 5) manufacturability and 6) recyclability. This roadmap should be seen as an enabling complement to the global battery roadmaps which focus on expected ultrahigh battery performance, especially for the future of transport. Batteries are used in many applications and are considered to be one technology necessary to reach the climate goals. Currently the market is dominated by lithium-ion batteries, which perform well, but despite new generations coming in the near future, they will soon approach their performance limits. Without major breakthroughs, battery performance and production requirements will not be sufficient to enable the building of a climate-neutral society. Through this “chemistry neutral” approach a generic toolbox transforming the way batteries are developed, designed and manufactured, will be created

Preparation, characterization and simulation studies of carbon nanotube electrodes for electrochemical energy storage

Chemical Vapor Deposition (CVD) was employed to synthesize multiwalled carbon nanotubes (MWCNT) on different carrier materials for electrode applications. In the field of electrochemical energy storage it is essential to grow MWCNT on conducting substrates. For this reason titanium nitride (TiN) layers as well as a copper foil were used as substrates. The MWCNT grown on TiN layers show diameters of about 20 nm and lengths up to 13 µm. In the case of copper foil substrates a remarkably higher nanotube diameter of several tens of nanometers was found. First electrochemical characterization via cyclic voltammetry shows the potential of MWCNT as electrodes for energy storage applications. The CNT were measured in an organic carbonate electrolyte vs. a lithium counter electrode with various scan rates. Until now the preliminary investigations by cyclic voltammetry for electrodes consisting of aligned MWCNT on TiN showed a capacity of around 130 F g-1 in the range of 1 - 3 V vs. Li/Li+. In support of the experiments we construct a one dimensional Poisson-Nernst-Planck (PNP) continuum model that has been shown to yield agreement with corresponding molecular dynamics simulations to model ion transport into these types of electrodes. Our simulations show that first the ions accumulate at the tips of the tubes because the inner volume of the electrodes is initially field-free. A homogeneous charge distribution is then established through diffusion. The PNP model is used to compute cyclic voltammograms which show qualitative agreement with the experiments

Hybrid Polymer Electrolytes Based on Linear Siloxane Networks and Crosslinked Polyether Domains: Interplay Between Composition and Properties

In this study, a new class of hybrid polymer electrolytes was prepared and characterized. The materials consisted of a matrix based on linear oligosiloxane networks and partially crosslinked polyether domains, doped with Lithium bis(trifluorosulfonyl)imide (LiTFSI). These materials are characterized by a maximum conductivity of 8 1910-5 S/cm at 30 \ub0C, and high thermo-mechanical stability, with decomposition temperature of 250 \ub0C and a storage shear modulus of almost 105 Pa at 100 \ub0C. Compositional parameters such as salt, cross-linker concentration, and polyether chain length were varied, and the materials were characterized by several analytical techniques. Vibrational spectroscopy provided details of the hybrid structure and the effect of salt doping. The thermo-mechanical properties were studied by thermogravimetric analysis, differential scanning calorimetry and rheological analysis. Finally, the transport properties were analyzed by means of broadband electric spectroscopy. The study made it possible to describe the relationships between composition, morphology, thermo-mechanical and transport properties of the synthesized hybrid electrolytes, with particular emphasis on the interplay between polymer dynamics and conduction mechanism