Correlating facet orientation, defect level density and dipole layer formation at the surface of polycrystalline CuInSe2 thin films

Individual grains of chalcopyrite solar cell absorbers can facet in different crystallographic directions at their surfaces. To gain a deeper understanding of the junction formation in these devices, we correlate variations in the surface facet orientation with the defect electronic properties. We use a combined ana lytical approach based on scanning tunneling spectroscopy STS , scanning electron microscopy, and elec tron back scatter diffraction EBSD , where we perform these experiments on identical surface areas as small as 2 2 amp; 956;m 2 with a lateral resolution well below 50 nm. The topography of the absorber sur faces indicates two main morphological features micro faceted, long basalt like columns and their short nano faceted terminations. Our STS results reveal that the long columns exhibit spectral signatures typ ical for the presence of pronounced oxidation induced surface dipoles in conjunction with an increased density of electronic defect levels. In contrast, the nano faceted terminations of the basalt like columns are largely passivated in terms of electronic defect levels within the band gap region. Corresponding crystallographic data based on EBSD experiments show that the surface of the basalt like columns can be assigned to intrinsically polar facet orientations, while the passivated terminations are assigned to non polar planes. Ab initio calculations suggest that the polar surfaces are more prone to oxidation and resulting O induced defects, in comparison to non polar planes. Our results emphasize the correlation between morphology, surface facet orientations and surface electronic properties. Furthermore, this work aids in gaining a fundamental understanding of oxidation induced lateral inhomogeneities in view of the p n junction formation in chalcopyrite thin film solar cell

Properties of Co Evaporated RbInSe2 Thin Films

The formation of an Rb containing In Se compound at the surface of Cu In, Ga Se2 CIGS thin films is assumed to be part of the mechanism of RbF post deposition treatments PDTs performed on these absorber layers. Alkali PDTs have acquired attention lately as they significantly enhance the efficiency of CIGS solar cells. In this contribution the formation of various phases during the RbF PDT has been investigated. The results indicate that RbInSe2 is the most probable phase to form. Combining theoretical and experimental investigations, fundamental properties of a thermally co evaporated RbInSe2 thin film are reported in order to serve as reference values in further studie

D-Praxis: A Peer-to-Peer Collaborative Model Editing Framework

International audienceLarge-scale industrial systems involve nowadays hundreds of developers working on hundreds of models representing parts of the whole system specification. Unfortunately, few tool support is provided for managing this huge set of models. In such a context of collaborative work, the approach commonly adopted by the industry is to use a central repository and to make use of merge mechanisms and locks.In this article we present a collaborative model editing framework, peer-to-peer oriented, that considers that every developer has his own partial replication of the system specification and that makes use of messages exchange for propagating changes made by developers. Our approach has the advantage not to be based on a single repository, which is more and more the case in large-scale industrial projects

Surface Passivation and Detrimental Heat Induced Diffusion Effects in RbF Treated Cu In,Ga Se2 Solar Cell Absorbers

Alkali postdeposition treatments of Cu In,Ga Se2 absorbers with KF, RbF, and CsF have led to remarkable efficiency improvements for chalcopyrite thin film solar cells. However, the effect of such treatments on the electronic properties and defect physics of the chalcopyrite absorber surfaces are not yet fully understood. In this work, we use scanning tunneling spectroscopy and X ray photoelectron spectroscopy to compare the surface defect electronic properties and chemical composition of RbF treated and nontreated absorbers. We find that the RbF treatment is effective in passivating electronic defect levels at the surface by preventing surface oxidation. Our X ray photoelectron spectroscopy XPS data points to the presence of chemisorbed Rb on the surface with a bonding configuration similar to that of a RbInSe2 bulk compound. Yet, a quantitative analysis indicates Rb coverage in the submonolayer regime, which is likely causing the surface passivation. Furthermore, ab initio calculations confirm that RbF treated surfaces are less prone to oxidation in the form of Ga, In, and Se oxides than bare chalcopyrite surfaces. In addition, elemental diffusion of Rb along with Na, Cu, and Ga is found to occur when the samples are annealed under ultrahigh vacuum conditions. Magnetic sector secondary ion mass spectrometry measurements indicate that there is a homogeneous spatial distribution of Rb on the surface both before and after annealing, albeit with an increased concentration at the surface after heat treatment. Depth resolved magnetic sector secondary ion mass spectrometry measurements show that Rb diffusion within the bulk occurs predominantly along grain boundaries. Scanning tunneling and XPS measurements after subsequent annealing steps demonstrate that the Rb accumulation at the surface leads to the formation of metallic Rb phases, involving a significant increase of electronic defect levels and or surface dipole formation. These results strongly suggest a deterioration of the absorber window interface because of increased recombination losses after the heat induced diffusion of Rb toward the interfac

Guidelines for the use of flow cytometry and cell sorting in immunological studies (second edition)

These guidelines are a consensus work of a considerable number of members of the immunology and flow cytometry community. They provide the theory and key practical aspects of flow cytometry enabling immunologists to avoid the common errors that often undermine immunological data. Notably, there are comprehensive sections of all major immune cell types with helpful Tables detailing phenotypes in murine and human cells. The latest flow cytometry techniques and applications are also described, featuring examples of the data that can be generated and, importantly, how the data can be analysed. Furthermore, there are sections detailing tips, tricks and pitfalls to avoid, all written and peer-reviewed by leading experts in the field, making this an essential research companion