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

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

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