Solar hydrogen has the potential to replace fossil fuels with a sustainable energy carrier that can be produced from sunlight and water via &quotewater splitting&quote. This study investigates the use of hematite (Fe&sub2O&sub3) as a photoelectrode for photoelectrochemical water splitting. Fe&sub2O&sub3 has a narrow indirect band-gap, which allows the utilization of a substantial fraction of the solar spectrum. However, the water splitting efficiencies for Fe&sub2O&sub3 are still low due to poor absorption characteristics, and large losses due to recombination in the bulk and at the surface. The thesis investigates the use of nanostructured composite electrodes, where thin films of Fe&sub2O&sub3 are deposited onto a nanostructured metal oxide substrate, in order to overcome some of the factors that limit the water splitting efficiency of Fe&sub2O&sub3. Doped (Si, Ti) and undoped Fe&sub2O&sub3 thin films were prepared using vacuum deposition techniques, and their photoelectrochemical, electrical, optical and structural properties were characterised. The doped Fe&sub2O&sub3 exhibited much higher photoelectrochemical activity than the undoped material, due to an improvement of the surface transfer coefficient and some grain boundary passivation. Schottky barrier modeling of Fe&sub2O&sub3 thin films showed that either the width of the depletion region or the diffusion length is the dominant parameter with a value around 30 nm, and confirmed that the surface charge transfer coefficient is small. An extensive review of the conduction mechanisms of Fe&sub2O&sub3 is presented. ZnO and SnO&sub2 nanostructures were investigated as substrates for the Fe&sub2O&sub3 thin films. Arrays of well-aligned high aspect ratio ZnO nanowires were optimised via the use of nucleation seeds and by restricting the lateral growth of the nanostructures. The geometry of the nanostructured composite electrodes was designed to maximise absorption and charge transfer processes. Composite nanostructured electrodes showed lower quantum efficiencies than equivalent thin films of Fe&sub2O&sub3, though a relative enhancement ofcollection of long wavelength charge carriers was observed, indicating that the nanostructured composite electrode concept is worthy of further investigation. The rate-limiting step for water splitting with Fe&sub2O&sub3 is not yet well understood and further investigations of the surface and bulk charge transfer properties are required in order to design electrodes to overcome specific shortcomings.

Solar hydrogen has the potential to replace fossil fuels with a sustainable energy carrier that can be produced from sunlight and water via &quotewater splitting&quote. This study investigates the use of hematite (Fe&sub2O&sub3) as a photoelectrode for photoelectrochemical water splitting. Fe&sub2O&sub3 has a narrow indirect band-gap, which allows the utilization of a substantial fraction of the solar spectrum. However, the water splitting efficiencies for Fe&sub2O&sub3 are still low due to poor absorption characteristics, and large losses due to recombination in the bulk and at the surface. The thesis investigates the use of nanostructured composite electrodes, where thin films of Fe&sub2O&sub3 are deposited onto a nanostructured metal oxide substrate, in order to overcome some of the factors that limit the water splitting efficiency of Fe&sub2O&sub3. Doped (Si, Ti) and undoped Fe&sub2O&sub3 thin films were prepared using vacuum deposition techniques, and their photoelectrochemical, electrical, optical and structural properties were characterised. The doped Fe&sub2O&sub3 exhibited much higher photoelectrochemical activity than the undoped material, due to an improvement of the surface transfer coefficient and some grain boundary passivation. Schottky barrier modeling of Fe&sub2O&sub3 thin films showed that either the width of the depletion region or the diffusion length is the dominant parameter with a value around 30 nm, and confirmed that the surface charge transfer coefficient is small. An extensive review of the conduction mechanisms of Fe&sub2O&sub3 is presented. ZnO and SnO&sub2 nanostructures were investigated as substrates for the Fe&sub2O&sub3 thin films. Arrays of well-aligned high aspect ratio ZnO nanowires were optimised via the use of nucleation seeds and by restricting the lateral growth of the nanostructures. The geometry of the nanostructured composite electrodes was designed to maximise absorption and charge transfer processes. Composite nanostructured electrodes showed lower quantum efficiencies than equivalent thin films of Fe&sub2O&sub3, though a relative enhancement ofcollection of long wavelength charge carriers was observed, indicating that the nanostructured composite electrode concept is worthy of further investigation. The rate-limiting step for water splitting with Fe&sub2O&sub3 is not yet well understood and further investigations of the surface and bulk charge transfer properties are required in order to design electrodes to overcome specific shortcomings.

Solar photovoltaic modules provide clean electricity from sunlight but will not be able to compete on an open market until the cost of the electricity they produce is comparable to that produced by traditional methods. At present, modules based on crystalline silicon wafer solar cells account for nearly 90% of photovoltaic production capacity. However, it is anticipated that the ultimate cost reduction achievable for crystalline silicon solar cell production will be somewhat limited and that thin film solar cells may offer a cheaper alternative in the long term. The highest energy conversion efficiencies reported for thin film solar cells have been for devices based around chalcopyrite Cu(In, Ga)(Se, S)2 photovoltaic absorbers. The most efficient Cu(In, Ga)(Se, S)2 solar cells contain absorber layers deposited by vacuum co-evaporation of the elements. However, the cost of ownership of large area vacuum evaporation technology is high and may be a limiting factor in the cost reductions achievable for Cu(In, Ga)(Se, S)2 based solar cells. Therefore, many alternative deposition methods are under investigation. Despite almost thirty companies being in the process of commercialising these technologies there is no consensus as to which deposition method will lead to the most cost effective product. Non-vacuum deposition techniques involving powders and chemical solutions potentially offer significant reductions in the cost of Cu(In, Ga)(Se, S)2 absorber layer deposition as compared to their vacuum counterparts. A wide range of such approaches has been investigated for thirty years and the gap between the world record Cu(In, Ga)(Se, S)2 solar cell and the best devices containing non-vacuum deposited absorber layers has closed significantly in recent years. Nevertheless, no one technique has demonstrated its superiority and the best results are still achieved with some of the most complex approaches. The work presented here involved the development and investigation of a new process for performing one of the stages of non-vacuum deposition of Cu(In, Ga)(Se, S)2 absorber layers. The new process incorporates copper into an initial Group III-VI precursor layer, e.g. indium gallium selenide, through an ion exchange reaction performed in solution. The ion exchange reaction requires only very simple, low-cost equipment and proceeds at temperatures over 1000°C lower than required for the evaporation of Cu under vacuum. In the new process, indium (gallium) selenide initial precursor layers are immersed in solutions containing Cu ions. During immersion an exchange reaction occurs and Cu ions from the solution exchange places with Group III ions in the layer. This leads to the formation of an intimately bonded, laterally homogeneous copper selenide – indium (gallium) selenide modified precursor layer with the same morphology as the initial precursor. These modified precursor layers were converted to single phase chalcopyrite CuInSe2 and Cu(In, Ga)Se2 by annealing with Se in a tube furnace system. Investigation of the annealing treatment revealed that a series of phase transformations, beginning at low temperature, lead to chalcopyrite formation. Control of the timing of the Se supply was demonstrated to prevent reactions that were deemed detrimental to the morphology of the resulting chalcopyrite layers. When vacuum evaporated indium (gallium) selenide layers were used as initial precursors, solar cells produced from the absorber layers exhibited energy conversion efficiencies of up to 4%. While these results are considered promising, the devices were characterised by very low open circuit voltages and parallel resistances. Rapid thermal processing was applied to the modified precursor layers in an attempt to further improve their conversion into chalcopyrite material. Despite only a small number of solar cells being fabricated using rapid thermal processing, improvements in open circuit voltage of close to 150mV were achieved. However, due to increases in series resistance and reductions in current collection only small increases in solar cell efficiency were recorded. Rapid thermal processing was also used to demonstrate synthesis of single phase CuInS2 from modified precursor layers based on non-vacuum deposited indium sulphide. Non-vacuum deposition methods provide many opportunities for the incorporation of undesirable impurities into the deposited layers. Analysis of the precursor layers developed during this work revealed that alkali atoms from the complexant used in the ion exchange baths are incorporated into the precursor layers alongside the Cu. Alkali atoms exhibit pronounced electronic and structural effects on Cu(In, Ga)Se2 layers and are beneficial in low concentrations. However, excess alkali atoms are detrimental to Cu(In, Ga)Se2 solar cell performance and the problems encountered with cells produced here are consistent with the effects reported in the literature for excess alkali incorporation. It is therefore expected that further improvements in solar cell efficiency might be achieved following reformulation of the ion exchange bath chemistry.

Vacuum deposition techniques like thermal evaporation and CVD with their precise layer control and high layer purity often cannot be applied for the deposition of chemical or biological molecules. The molecules are usually decomposed by heat. To overcome this problem, the Electrospray ionization (ESI) process known from mass spectroscopy is employed to transfer molecules into vacuum and to deposit them on a substrate. In this work, a homemade ESI tool was used to deposit BSA (Bovine serum albumin) layers with high deposition rates. Solutions with different concentrations of BSA were prepared using a methanol:water (MeOH:H2O) mixture (1:1) as solvent. The influence of the substrate distance on the deposition rate and on the transmission current was analyzed. Furthermore, the layer thickness distribution and layer adhesion were investigated.

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 86 / In 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 86

>Magister Scientiae - MSc / To study nuclear reactions and nuclear structures, target materials are bombarded with high-energy particles. The target material can either be in a form of a metal film or gas. A target material designed to study certain nuclear reactions or to produce nuclei to study their structure should yield as minimum as possible of competing reactions under ion bombardment. This requires a chemically and isotopically pure target material prepared as a self supporting thin film, or as alternative, prepared on a thin career foil. Additional requirement for lifetime measurement experiments are homogeneity and precise thickness of the target material. Some of the data obtained from the stopping power experiment where targets of 114Cd were used for lifetime measurement are presented. Moreover, a nuclear target should influence the spectroscopic resolution as little as possible. Thus, film thickness must be adjusted to the respective reaction under study while observing the optimum thickness homogeneity.

Le contexte du réchauffement climatique entraîne un développement des technologies CSP (Concentrated Solar Power). La réduction des coûts de production de ces technologies passe par une amélioration de la durabilité et de l'efficacité des composants des centrales solaires. Les températures de fonctionnement élevées du CSP (250-600°C) nécessitent d'employer des absorbeurs spectralement sélectifs afin de limiter les pertes par radiation. Cette thèse propose une architecture originale d'absorbeurs sélectifs stables à haute température sous air en combinant un dépôt de TiAlN en couches minces avec un réseau de diffraction. L'ajout d'une texturation de surface augmente l'absorption solaire du dépôt par un effet d'absorption et de gradient des indices optiques effectifs conduisant à une augmentation du rendement photothermique de l'absorbeur. Dans ce mémoire, la modélisation du comportement optique des absorbeurs texturés, les méthodes de fabrication du réseau de diffraction ainsi que le dépôt des couches minces par PVD et PECVD seront abordés et les mesures expérimentales seront comparées aux modélisations. L'analyse des absorbeurs texturés fabriqués confirme un gain de rendement photothermique pouvant atteindre +3% ainsi qu'une stabilité thermique remarquable à 500°C sous air jusqu'à 300 h de recuit / The global warming context reinforces the development of CSP technologies. Cost reduction of CSP requires the improvement of component durability and efficiency. The solar absorbers should be spectrally selective since the high working temperatures of CSP plants increase the radiative thermal losses. This thesis proposes an original, spectrally selective absorber structure combining TiAlN based coatings and diffractive gratings. The surface texturing provided by the diffractive gratings improves the solar absorption of the thin coating by an effective optical index gradation effect leading toincreased photothermal efficiency. In this thesis, the modeling of the textured absorber’s optical behavior, fabrication methods of diffractive gratings, as well as layer deposition by PVD/PECVD will be discussed. Experimental measurements will be compared to the theoretical modelling. The experimental analysis of textured absorbers confirms the increase of photothermal efficiency by almost 3%, as well as a good thermal stability at 500°C in air for 300 hours of annealing

This work aims at improving the understanding of the fundamental physics behind molecular doping of organic semiconductors, being a requirement for efficient devices like organic light-emitting diodes (OLED) and organic photovoltaic cells (OPV). The underlying physics is studied by electrical conductivity and thermoelectrical Seebeck measurements and the influences of doping concentration and temperature are investigated. Thin doped layers are prepared in vacuum by thermal co-evaporation of host and dopant molecules and measured in-situ. The fullerene C60, known for its high electron mobility, is chosen as host for five different n-dopants. Two strongly ionizing air-sensitive molecules (Cr2(hpp)4 and W2(hpp)4) and three air-stable precursor compounds (AOB, DMBI-POH and o-MeO-DMBI-I) which form the active dopants upon deposition are studied to compare their doping mechanism. High conductivities are achieved, with a maximum of 10.9 S/cm. Investigating the sample degradation by air-exposure, a method for regeneration is proposed, which allows for device processing steps under ambient conditions, greatly enhancing device fabrication possibilities. Various material combinations for p-doping are compared to study the influence of the molecular energy levels of host (MeO-TPD and BF-DPB) and dopant (F6-TCNNQ and C60F36). Corrections for the only estimated literature values for the dopant levels are proposed. Furthermore, the model system of similar-sized host pentacene and dopant F4-TCNQ is studied and compared to theoretical predictions. Finally, a model is developed that allows for estimating charge carrier mobility, density of free charge carriers, doping efficiency, as well as the transport level position from combining conductivity and Seebeck data. / Diese Arbeit untersucht organische Halbleiter und den Einfluss von molekularer Dotierung auf deren elektrische Eigenschaften, mit dem Ziel effizientere Bauelemente wie organische Leuchtdioden oder Solarzellen zu ermöglichen. Mittels Leitfähigkeitsuntersuchungen sowie thermoelektrischen Seebeck-Messungen werden die Einflüsse der Dotierkonzentration sowie der Temperatur auf die elektrischen Eigenschaften dünner dotierter Schichten analysiert. Das Abscheiden der Schichten durch Koverdampfen im Vakuum ermöglicht eine in-situ Analyse. Das Fulleren C60, bekannt für besonders hohe Elektronenbeweglichkeit, wird als Wirt für fünf verschieden n-Dotanden, zwei extrem stark ionisierende luftreaktive (Cr2(hpp)4 und W2(hpp)4) sowie drei luftstabile (AOB, DMBI-POH und o-MeO-DMBI-I), verwendet. Dies ermöglicht Schlüsse auf die unterschiedlichen zugrunde liegenden Dotiermechanismen und das Erreichen von Leitfähigkeiten von bis zu 10.9 S/cm. Für einen der luftreaktiven Dotanden wird die Probendegradation an Luft untersucht und eine Regenerationsmethode aufgezeigt, die Prozessierungsschritte in Luft erlaubt und somit entscheidend für zukünftige Bauelementfertigung sein könnte. Verschiedene p-dotierte Materialkombinationen werden untersucht, um den Einfluss der molekularen Energieniveaus von Wirt (MeO-TPD und BF-DPB) und Dotand (F6-TCNNQ und C60F36) auf die Dotierung zu studieren. Dies ermöglicht Schlussfolgerungen auf die in der Literatur bisher nur abgeschätzten Energieniveaus dieser Dotanden. Ferner werden die Eigenschaften des bereits theoretisch modellierten Paares Pentacen und F4-TCNQ mit den Vorhersagen verglichen und die Abweichungen diskutiert. Abschießend wird ein Modell entwickelt, das die Abschätzung von Dotiereffizienz, Ladungsträgerkonzentration, Ladungsträgerbeweglichkeit sowie der Position des Transportniveaus aus Leitfähigkeits- und Seebeck-Messungen erlaubt.

This thesis discusses vacuum deposited organic solar cells. It focuses on the investigation of new donor molecules blended with the standard electron acceptor C60. These donor-acceptor heterojunctions form the photoactive system of organic solar cells. In addition, the influence of the processing conditions on the morphology of the blend layers is investigated, as the morphology is crucial for an efficient generation of free charge carriers upon photon absorption. Bulk heterojunction solar cells with the donor DTDCTB are deposited at different substrate temperatures. We identify three substrate temperature regimes, discriminated by the behavior of the fill factor (FF ) as a function of the blend layer thickness. Devices deposited at RT have a maximum FF between 50 and 70 nm blend thickness, while devices deposited at 110 °C have a monotonically decreasing FF. At Tsub=85 °C, the devices have an S-kinked current-voltage curve. Grazing incidence wide angle X-ray scattering measurements show that this peculiar behavior of the FF is not correlated with a change in the crystallinity of the DTDCTB, which stays amorphous. Absorption measurements show that the average alignment of the molecules inside the blend also remains unchanged. Charge extraction measurements (OTRACE) reveal a mobility for the 110 °C device that is an order of magnitude higher than for the RT device. The difference in mobility can be explained by a higher trap density for the RT samples as measured by impedance spectroscopy. Despite slightly higher carrier lifetimes for the RT device obtained by transient photovoltage measurements, its mobility-lifetime product is still lower than for the 110 °C devices. Based on DTDCTB, three new donor materials are designed to have a higher thermal stability in order to achieve higher yields upon material purification using gradient sublimation. For PRTF, the thermal stability is increased demonstrated by a higher yield upon sublimation. However, all new materials have a reduced absorption as compared to DTDCTB, which limits the short current density, and the FF is more sensitive to an increase of the blend layer thickness. The highest power conversion efficiency is achieved for a PRTF:C60 solar cell with 3.8%. Interestingly, PRTF:C60 solar cells show exceptionally low nonradiative voltage losses of only 0.26 V. Another absorber molecule is the push-pull chromophore QM1. Scanning electron microscope (SEM) measurements show a growth of the molecule in nanowires on several substrates. The nanowires have lengths up to several micrometers and are several tens of nanometers wide. The formation of the nanowires is accompanied by a strong blue shift (650 meV) of the thin film absorption spectrum in comparison to the absorption in solution, which is attributed to H-aggregation of the molecules. Furthermore, the thin film absorption onset reaches up to 1100 nm, making the material a suitable candidate for a near infrared absorber in organic solar cells. For a solar cell in combination with C60, a power conversion efficiency of 1.9% was achieved with an external quantum efficiency of over 19% for the spectral range between 600 and 1000 nm. The method of “co-evaporant induced crystallization” as a means to increase the crystallinity of blend layers without increasing the substrate temperature during the deposition is investigated. Mass spectrometry (LDI-ToF-MS) measurements show that polydimethylsiloxane (PDMS), which is used as a co-evaporant, decomposes during the evaporation and only lighter oligomers evaporate. Quartz crystal microbalance (QCM) measurements prove that the detection of PDMS saturates at higher amounts of evaporated material. LDI-ToF-MS measurements show further that the determination of the volatilization temperature by QCM measurements is highly error prone. The method was applied to zinc phthalocyanine (ZnPc) :C60 solar cells, accepting the insertion of PDMS into the blend layer. Diffraction (GIXRD) measurements show a large increase in crystallinity. ZnPc:C60 solar cells produced by applying the method reveal a similar behavior as solar cells processed at a higher substrate temperature.

This thesis discusses vacuum deposited organic solar cells. It focuses on the investigation of new donor molecules blended with the standard electron acceptor C60. These donor-acceptor heterojunctions form the photoactive system of organic solar cells. In addition, the influence of the processing conditions on the morphology of the blend layers is investigated, as the morphology is crucial for an efficient generation of free charge carriers upon photon absorption. Bulk heterojunction solar cells with the donor DTDCTB are deposited at different substrate temperatures. We identify three substrate temperature regimes, discriminated by the behavior of the fill factor (FF ) as a function of the blend layer thickness. Devices deposited at RT have a maximum FF between 50 and 70 nm blend thickness, while devices deposited at 110 °C have a monotonically decreasing FF. At Tsub=85 °C, the devices have an S-kinked current-voltage curve. Grazing incidence wide angle X-ray scattering measurements show that this peculiar behavior of the FF is not correlated with a change in the crystallinity of the DTDCTB, which stays amorphous. Absorption measurements show that the average alignment of the molecules inside the blend also remains unchanged. Charge extraction measurements (OTRACE) reveal a mobility for the 110 °C device that is an order of magnitude higher than for the RT device. The difference in mobility can be explained by a higher trap density for the RT samples as measured by impedance spectroscopy. Despite slightly higher carrier lifetimes for the RT device obtained by transient photovoltage measurements, its mobility-lifetime product is still lower than for the 110 °C devices. Based on DTDCTB, three new donor materials are designed to have a higher thermal stability in order to achieve higher yields upon material purification using gradient sublimation. For PRTF, the thermal stability is increased demonstrated by a higher yield upon sublimation. However, all new materials have a reduced absorption as compared to DTDCTB, which limits the short current density, and the FF is more sensitive to an increase of the blend layer thickness. The highest power conversion efficiency is achieved for a PRTF:C60 solar cell with 3.8%. Interestingly, PRTF:C60 solar cells show exceptionally low nonradiative voltage losses of only 0.26 V. Another absorber molecule is the push-pull chromophore QM1. Scanning electron microscope (SEM) measurements show a growth of the molecule in nanowires on several substrates. The nanowires have lengths up to several micrometers and are several tens of nanometers wide. The formation of the nanowires is accompanied by a strong blue shift (650 meV) of the thin film absorption spectrum in comparison to the absorption in solution, which is attributed to H-aggregation of the molecules. Furthermore, the thin film absorption onset reaches up to 1100 nm, making the material a suitable candidate for a near infrared absorber in organic solar cells. For a solar cell in combination with C60, a power conversion efficiency of 1.9% was achieved with an external quantum efficiency of over 19% for the spectral range between 600 and 1000 nm. The method of “co-evaporant induced crystallization” as a means to increase the crystallinity of blend layers without increasing the substrate temperature during the deposition is investigated. Mass spectrometry (LDI-ToF-MS) measurements show that polydimethylsiloxane (PDMS), which is used as a co-evaporant, decomposes during the evaporation and only lighter oligomers evaporate. Quartz crystal microbalance (QCM) measurements prove that the detection of PDMS saturates at higher amounts of evaporated material. LDI-ToF-MS measurements show further that the determination of the volatilization temperature by QCM measurements is highly error prone. The method was applied to zinc phthalocyanine (ZnPc) :C60 solar cells, accepting the insertion of PDMS into the blend layer. Diffraction (GIXRD) measurements show a large increase in crystallinity. ZnPc:C60 solar cells produced by applying the method reveal a similar behavior as solar cells processed at a higher substrate temperature.