This thesis consists of three main studies: magnetic field effects in thermally activated delayed fluorescent (TADF) organic light emitting diodes (OLEDs), magnetic field effects in bipolar and unipolar polythiophene (P3HT) devices and a study of hybrid organic/inorganic perovskite devices. Spin-dependent transport and recombination processes of spin-pair species have been detected by magnetic field effect (MFE) technique in carbon-based semi- conductor devices. Magneto-electroluminescence (MEL) and magneto-conductivity have been measured as a function of the applied magnetic field, B, in light emitting diodes. TADF materials have been used instead of simple fluorescent materials in OLEDs. We have observed very large magnetic response with TADF materials. The second study is magnetic field effects of regio-regular P3HT based OLED devices. P3HT is a well known semiconducting polymer, and its electrical properties such as magneto-conductance can be affected by an applied magnetic field. P3HT was chosen because it exhibits a sign change in magnetoresistance (MR) as the bias is increased. Unipolar and bipolar devices have been fabricated with different electrode materials to understand which model can be best to explain organic magnetoresistance effect, possibly depending on the operating regime of the device. Transport and luminescence spectroscopies were studied to isolate the different mechanisms and identify their fingerprints. The third study is on hybrid organic-inorganic perovskite devices. With the potential of achieving very high efficiencies and the very low production costs, perovskite solar cells have become commercially attractive. Scanning electron microscopy (SEM) images and absorption spectrum of the films were compared in single-step solution, two-step solution and solution-assisted vapor deposition techniques. Grain size, morphology and thickness parameters of perovskite films were studied within these techniques. Perovskite solar cells were fabricated and their efficiencies were measured.

>Magister Scientiae - MSc / Organic-inorganic lead-based perovskite has exhibited great performance in the past few years. However, the lead (Pb) embedded in those compounds is a significant drawback to further progress, due to its environmental toxicity. As an alternative, tin (Sn) based-perovskites have demonstrated promising results in terms of electrical and optical properties for photovoltaic devices, but the oxidation of tin ion- from stannous ion (Sn2+) to stannic ion (Sn4+) presents a problem in terms of performance and stability when exposed to ambient conditions. A more feasible approach may be in a Pb-Sn binary metal perovskite in pursuit of efficient, stable perovskite solar cells (PSCs) with reduced Pb-content, as compared to pure Pb- or Sn-based PSCs. Here, we report on the deposition of a Pb-Sn binary perovskite by sequential chemical vapor deposition.

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第20405号 / 工博第4342号 / 新制||工||1673(附属図書館) / 京都大学大学院工学研究科高分子化学専攻 / (主査)教授 大北 英生, 教授 赤木 和夫, 教授 木村 俊作 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DGAM

Der Schwerpunkt der vorliegenden Arbeit liegt in der Charakterisierung der elektronischen Eigenschaften von hybriden organisch-anorganischen Perowskit (HOIP)-Schichten während der Schichtbildung und in verschiedenen Umgebungen mittels Photoelektronenspektroskopie (PES). Insbesondere wird der Methylammonium-Blei-Iodid-Chlorid-Perowskit (MAPbI3-xClx) untersucht. Als erstes werden Änderungen in den elektronischen Eigenschaften, der Zusammensetzung, sowie der Kristallstruktur mittels PES, Flugzeit-Sekundärionenmassenspektrometrie, sowie Röntgendiffraktometrie mit streifendem Einfall analysiert. Die Resultate weisen auf die entscheidende Rolle von Chlor im texturierten Wachstum der Perowskitschicht hin. Die auskristallisierte Perowskitschicht weist eine stärkere n-Typ Eigenschaft auf, welche auf die Änderung der Zusammensetzung während der Schichtbildung zurückgeführt werden kann. Außerdem beweisen die Ergebnisse eindeutig die Ablagerung von Chlor an der Grenzfläche zwischen der Perowskitschicht und dem Substrat. Zweitens werden die separaten Einflüsse von Wasser, Sauerstoff, und Umgebungsluft auf die elektronischen Eigenschaften von MAPbI3-xClx-Schichtoberflächen untersucht. Bereits geringste Wassermengen ähnlich wie im Hochvakuum oder in inerter Umgebung können eine reversible Reduzierung der Austrittsarbeit hervorrufen. Höherer Wasserdampf-Partialdruck führt zu einer Verschiebung des Valenzbandmaximums (VBM) weit vom Fermi-Niveau, sowie zu einer Reduzierung der Austrittsarbeit. Im Gegensatz dazu führt eine Sauerstoffexposition zu einer Verschiebung des VBM in Richtung des Fermi-Niveaus und zu einer Steigerung der Austrittsarbeit. Analog kommt es zu einer Verschiebung von bis zu 0.6 eV bei einer Exposition gegenüber Umgebungsluft, was den vorwiegenden Einfluss von Sauerstoff demonstriert. Die vorliegenden Untersuchungen betonen den kritischen Einfluss der Schichtbildung, der Zusammensetzung, sowie der Umgebungsbedingungen auf die elektronischen Eigenschaften von HOIP. / The present thesis aims at characterizing the electronic properties of solution-processed hybrid organic-inorganic perovskites (HOIPs) in general, and the HOIP methyl ammonium (MA) lead iodide-chloride (MAPbI3-xClx) films, in particular, at different stages, namely from its formation to its degradation, by means of photoelectron spectroscopy (PES). Firstly, the formation of MAPbI3-xClx films upon thermal annealing is monitored by a combination of PES, time-of-flight secondary ion mass spectrometry, and grazing incidence X-ray diffraction for disclosing changes in electronic properties, film composition, and crystal structure, respectively. Overall, the results point to the essential mediating role of chlorine in the formation of a highly textured perovskite film. The film formation is accompanied by a change of composition which leads to the film becoming more n-type. The accumulation of chlorine at the interface between perovskite and the underlying substrate is also unambiguously revealed. Secondly, the separate effects of water and oxygen on the electronic properties of MAPbI3-xClx film surfaces are investigated by PES. Already low water exposure – as encountered in high vacuum or inert conditions – appears to reversibly impact the work function of the film surfaces. Water vapor in the mbar range induces a shift of the valence band maximum (VBM) away from the Fermi level accompanied by a decrease of the work function. In contrast, oxygen leads to a VBM shift towards the Fermi level and a concomitant increase of the work function. The effect of oxygen is found to predominate in ambient air with an associated shift of the energy levels by up to 0.6 eV. Overall, the findings contribute to an improved understanding of the structure-property relationships of HOIPs and emphasize the impact of least variation in the environmental conditions on the reproducibility of the electronic properties of perovskite materials.