Rate optimal estimation of quadratic functionals in inverse problems with partially unknown operator and application to testing problems

We consider the estimation of quadratic functionals in a Gaussian sequence model where the eigenvalues are supposed to be unknown and accessible through noisy observations only. Imposing smoothness assumptions both on the signal and the sequence of eigenvalues, we develop a minimax theory for this problem. We propose a truncated series estimator and show that it attains the optimal rate of convergence if the truncation parameter is chosen appropriately. Consequences for testing problems in inverse problems are equally discussed: in particular, the minimax rates of testing for signal detection and goodness-of-fit testing are derived.Comment: Corrected some typo

Physical vapour deposition of perovskite for solar cell applications

Hybride Metall-Halogen Perowskit basierte Solarzellen haben im letzten Jahrzehnt eine noch nie dagewesene Entwicklung hinsichtlich ihrer Effizienzsteigerung erzielt. Dies ging mit einem rapiden Anstieg des Interesses der Forschungsgemeinschaft einher. Ein wichtiger Faktor für die Realisierung von Forschungsergebnissen ist der Übergang von Laborskalen zu industriellen Dimensionen, was grundlegende Anpassungen im Herstellungsprozess notwenig macht. Hier hat sich die physikalische Gasphasenabscheidung für andere Materialklassen bereits als gute Lösung bei der Herstellung von qualitativ hochwertigen Dünnschichten erwiesen. In dieser Arbeit wird die Vakuumabscheidung von FA₁ ₋ ₓCsₓPbI₃ ₋ ₓBrₓ für die Anwendung in Solarzellen durch Dreiquellenkoverdampfung erforscht. Durch eine Kombination aus optischen und Röntgen-basierten Messverfahren konnte eine Veränderung der Aufnahme des organischen Halogensalzes, Formamidiniumiodid (FAI), in die Perowkitverbindung in Abhängigkeit vom Kammerdruck festgestellt werden. Dadurch tritt eine Stöchiometrieänderung auf, welche sich in einer Bandlückenverschiebung niederschlägt. Außerdem wurde eine Veränderung der Kristallitorientierung beobachtet. Diese Ergebnisse motivieren eine genauere Untersuchung des Verdampfungsverhaltens des organischen Halogensalzes. Mit Hilfe von Massenspektrometriemessungen und einer detaillierten Erfassung der Prozessparameter konnte eine Zersetzung von FAI während der Verdampfung festgestellt werden. Desweiteren wurden weitere Besonderheiten im Abscheideverhalten, wie zum Beispiel Verdampfunsgrenzen und Veränderungen des Toolingfaktors beobachtet. Die Ergebnisse leisten einen wesentlichen Beitrag zum tieferen Verständnis der Vakuumabscheidung von organischinorganischen Metall-Halogen Perowskiten.:Kurzfassung iv Abstract v List of publications vi 1. Introduction 1 2. Theoretical background 5 2.1. Basics of thin-_lm solar cells . . . . . . . . . . . . . . . . . . . . . . . . . 5 2.2. Status of current thin-_lm solar cell technologies . . . . . . . . . . . . 7 2.3. The Perovskite system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 2.4. Organic-inorganic mixed-halide metal perovskites . . . . . . . . . . . 14 2.5. Deposition methods of metal halide perovskite . . . . . . . . . . . . . 18 2.6. Vacuum deposition of perovskite . . . . . . . . . . . . . . . . . . . . . . 21 3. Experimental methods 27 3.1. Physical vapor deposition . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 3.2. Vacuum deposition of perovskite layers . . . . . . . . . . . . . . . . . . 29 3.3. Analytical techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 4. Pressure dependent triple-source co-evaporation of methylammoniumfree perovskite 39 4.1. Precursor puri_cation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 4.2. Film deposition procedure . . . . . . . . . . . . . . . . . . . . . . . . . . 42 4.3. Crystallographic characterisation . . . . . . . . . . . . . . . . . . . . . . 43 4.4. Optical characterisation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49 4.5. Incorporation of FAI into thin-_lms . . . . . . . . . . . . . . . . . . . . . 50 4.6. Photovoltaic devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51 4.7. Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55 5. Evaporation properties of formamidinium iodide 57 5.1. Degradation reactions of formamidinium iodide . . . . . . . . . . . . 57 5.2. Evaporation behaviour of formamidinium iodide . . . . . . . . . . . . 58 5.3. Theoretical considerations during the deposition process . . . . . . 61 5.4. Tooling behaviour of Formamidinium iodide . . . . . . . . . . . . . . . 63 5.5. Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68 6. Summary & Outlook 71 A. Appendix 75 List of Figures 81 List of Tables 82 List of Abbreviations 86 Bibliography 86In the last decade, hybrid metal halide perovskite-based solar cells have enjoyed an unprecedented surge in development within the research community. The next steps to further improve this technology will involve the transition from the laboratory to commercial-scale production, which will require adjustments in their fabrication processes. Here, physical vapour deposition has proven to be a good option for the fabrication of high-quality thin films for perovskites and other materials, like organic semiconductors. In this work, triple-source co-evaporation deposition of FA₁ ₋ ₓCsₓPbI₃ ₋ ₓBrₓ for the production of thin films for solar cell applications is investigated. With a combination of optical and X-ray-based measurement methods, a decrease in the incorporation of the organic halide salt formamidinium iodide (FAI) was found with increasing background pressure. This decrease results in a change in stoichiometry of the compound and, with it, a shift of the band gap. Furthermore, a change in crystallite orientation was observed. These findings motivate the examination of the evaporation behaviour of formamidinium iodide in more detail. With mass spectrometry measurements and detailed tracking of the process parameters, a degradation of FAI during evaporation was found. Furthermore, several effects of the deposition behaviour, evaporation limits, and tooling shifts were observed. These findings will be substantial for the deeper understanding of vacuum deposition of organic-inorganic metal halide perovskites, and will be significant in the expansion of perovskite-based solar technology.:Kurzfassung iv Abstract v List of publications vi 1. Introduction 1 2. Theoretical background 5 2.1. Basics of thin-_lm solar cells . . . . . . . . . . . . . . . . . . . . . . . . . 5 2.2. Status of current thin-_lm solar cell technologies . . . . . . . . . . . . 7 2.3. The Perovskite system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 2.4. Organic-inorganic mixed-halide metal perovskites . . . . . . . . . . . 14 2.5. Deposition methods of metal halide perovskite . . . . . . . . . . . . . 18 2.6. Vacuum deposition of perovskite . . . . . . . . . . . . . . . . . . . . . . 21 3. Experimental methods 27 3.1. Physical vapor deposition . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 3.2. Vacuum deposition of perovskite layers . . . . . . . . . . . . . . . . . . 29 3.3. Analytical techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 4. Pressure dependent triple-source co-evaporation of methylammoniumfree perovskite 39 4.1. Precursor puri_cation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 4.2. Film deposition procedure . . . . . . . . . . . . . . . . . . . . . . . . . . 42 4.3. Crystallographic characterisation . . . . . . . . . . . . . . . . . . . . . . 43 4.4. Optical characterisation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49 4.5. Incorporation of FAI into thin-_lms . . . . . . . . . . . . . . . . . . . . . 50 4.6. Photovoltaic devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51 4.7. Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55 5. Evaporation properties of formamidinium iodide 57 5.1. Degradation reactions of formamidinium iodide . . . . . . . . . . . . 57 5.2. Evaporation behaviour of formamidinium iodide . . . . . . . . . . . . 58 5.3. Theoretical considerations during the deposition process . . . . . . 61 5.4. Tooling behaviour of Formamidinium iodide . . . . . . . . . . . . . . . 63 5.5. Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68 6. Summary & Outlook 71 A. Appendix 75 List of Figures 81 List of Tables 82 List of Abbreviations 86 Bibliography 8

On rate optimal private regression under local differential privacy

We consider the problem of estimating a regression function from anonymized data in the framework of local differential privacy. We propose a novel partitioning estimate of the regression function, derive a rate of convergence for the excess prediction risk over H\"older classes, and prove a matching lower bound. In contrast to the existing literature on the problem the so-called strong density assumption on the design distribution is obsolete.Comment: Revised versio

Automated Cryptanalysis of Bloom Filter Encryptions of Health Records

Privacy-preserving record linkage with Bloom filters has become increasingly popular in medical applications, since Bloom filters allow for probabilistic linkage of sensitive personal data. However, since evidence indicates that Bloom filters lack sufficiently high security where strong security guarantees are required, several suggestions for their improvement have been made in literature. One of those improvements proposes the storage of several identifiers in one single Bloom filter. In this paper we present an automated cryptanalysis of this Bloom filter variant. The three steps of this procedure constitute our main contributions: (1) a new method for the detection of Bloom filter encrytions of bigrams (so-called atoms), (2) the use of an optimization algorithm for the assignment of atoms to bigrams, (3) the reconstruction of the original attribute values by linkage against bigram sets obtained from lists of frequent attribute values in the underlying population. To sum up, our attack provides the first convincing attack on Bloom filter encryptions of records built from more than one identifier.Comment: Contribution to the 8th International Conference on Health Informatics, Lisbon 201

Probing the nucleon at large momentum tramsfer

The central role of soft nucleon matrix elements in reactions of high energy electrons or real photons with nucleons is emphasized. These soft matrix elements are described in terms of skewed parton distributions. Their connections to ordinary parton distributions, form factors, Compton scattering and hard meson electroproduction is discussed.Comment: 11 pages, 12 Postscript figures, fleqn, espcrc1, epsfi