In this study, silicon nanocrystals (NC) were synthesized in silicon dioxide matrix by ion implantation followed by high temperature annealing. Annealing temperature and duration were varied to study their effect on the nanocrystal formation and optical properties. Implantation of silicon ions was performed with different energy and dose depending on the oxide thickness on the silicon substrate. Before device fabrication, photoluminescence (PL) measurement was performed for each sample. From PL measurement it was observed that, PL emission depends on nanocrystal size determined by the parameters of implantation and annealing process. The peak position of PL emission was found to shifts toward higher wavelength when the dose of implanted Si increased. Two PL emission bands were observed in most cases. PL emission around 800 nm originated from Si NC in oxide matrix. Other emissions can be attributed to the luminescent defects in oxide or oxide/NC interface. In order to see electroluminescence properties Light Emitting Devices (LED) were fabricated by using metal oxide semiconductor structure, current-voltage (I-V) and electroluminescence (EL) measurements were conducted. I-V results revealed that, current passing through device depends on both implanted Si dose and annealing parameters. Current increases with increasing dose as one might expect due to the increased amount of defects in the matrix. The current however decreases with increasing annealing temperature and duration, which imply that, NC in oxide behave like a well controlled trap level for charge transport. From EL measurements, few differences were observed between EL and PL results. These differences can be attributed to the different excitation and emission mechanisms in PL and EL process. Upon comparision, EL emission was found to be inefficient due to the asymmetric charge injection from substrate and top contact. Peak position of EL emission was blue shifted with respect to PL one, and approached towards PL peak position as applied voltage increased. From the results of the EL measurements, EL emission mechanisms was attributed to tunneling of electron hole pairs from top contact and substrate to NC via oxide barrier.

This thesis concerns with electrical and optoelectical properties of thin organic semiconductor layers. In the research, organic electroluminescent devices were prepared and the effect of illumination and inclusion of organic interlayers, that act as alternative electrodes, on charge injection and transport were investigated on them by means of electrical measurement and impedance spectroscopy. On the basis of measured data, the thesis attempts to determine materials best suited for interlayers, which could make an improvement of electric properties of electroluminescent devices possible. The sence of using a combination of direct current measurement and impedance spectroscopy was also discussed in the thesis.

This thesis discusses modern methods for fast defect detection of solar cells. For the means of the defect classification, the technological production process of crystalline silicon solar cells is described. The defects are researched by the electroluminescence and prohtoluminescence methods. The Photoluminiscence method is improved by the posibility of using different wavelenght of excitacion sources. The range of using in industrial production is determined for the discussed methods.

The aim of the diploma work is to introduce analytical methods concerning solar panels and systems. Firstly, the attention is drawn to a principle of photovoltaic conversion including an explanation of photoelectric phenomenon as well as the issue of P-N junction considered to be the fundamental building block of a solar cell. With respect to the fact that the diploma work is to be focused on testing of solar panels and the identification of defects in solar cells, the work describes individual solar cells, solar panels as well as individual methods of defect identification. Secondly, the work includes sections dealing with the assessment of the measurement performed by using electroluminescence method as well as the measurement method of volt-ampere parameters. The last section of the work includes the assessment of solar panel aging after one-year performance using the electroluminescence measurement method.

Die vorliegende Arbeit beschäftigt sich mit dem Aufbau von Nanokristall-LEDs. Dazu werden der Synthese, der Abscheidung und dem Aufbau und der Charakterisierung von Nanopartikeln und LEDs Platz eingeräumt. CdTe-Nanopartikel werden über eine wässrige Synthese, die auf elektrochemisch erzeugten Tellurwasserstoff beruhte, hergestellt. Der Vorteil besteht im geringen Aufwand und der guten Reproduzierbarkeit. Es konnte festgestellt werden, dass sich ein hoher Überschuss an Cadmiumionen in der Lösung positiv auf die Wachstumsgeschwindigkeit der Nanopartikel auswirkt. Statt des anfänglich benutzten Layer-by-Layer-Tauchverfahrens wurde ein Layer-by-Layer-Sprühverfahren entwickelt, das die schnelle Herstellung homogener Filme, bestehend aus alternierenden Schichten einer Matrix und der Nanopartikel, ermöglichte. Nachteilig ist der hohe Verbrauch an Nanopartikeln gegenüber dem Tauchverfahren. Dem Tauchverfahren lastet der Umstand an, die kolloidalen Lösungen durch häufiges Eintauchen des Substrats zu verunreinigen. Dies wird beim Sprühverfahren vermieden, da alles nicht adsorbierte Material nach unten abfließt. Es wurde gezeigt, dass sich Polyelektrolyte durch anorganische Gele ersetzen lassen, die über einen Sol-Gel-Prozess darstellbar sind, wobei es möglich wurde „All inorganic“-LEDs aufzubauen mit dem Vorteil der hohen Temperaturstabilität. Wobei sich die Reinheit der dargestellten Aluminiumoxid-Sole stark auf das Bestreben Aluminiumoxid-Kristalle zu bilden, auswirkt, die die Funktionsfähigkeit der LED behindern können. Die Verwendung einer isolierenden Matrix wie Poly-(diallyldimethylammoniumchlorid) oder Aluminiumoxid als Zwischenschicht zum Aufbau von mehrlagigen Nanopartikelschichten stellte sich als unproblematisch heraus, da sich Ladungsträger über einen „hopping“-Mechanismus zwischen den Halbleiternanopartikeln bewegen können. Größere Probleme bereitete die Verwendung von Nanopartikeln größerer Bandlücken wie ZnSe (2,7eV) als Elektrolumineszenz-Emitter. Es konnte nur eine weissbläuliche Emission beobachtet werden. Mit Nanopartikeln kleiner Bandlücke wie CdTe (1,6eV) wurde eine schmalbandige rote Emission festgestellt. Vorteilhaft erwies sich die Verwendung von Kern-Schale-Teilchen wie CdSe/CdS. Mit einer Matrix aus Aluminiumoxid-Gel konnte eine LED mit sehr niedriger Onset-Spannung (2,3V) hergestellt werden, die eine Lebensdauer von 33,5h besaß und noch bei einer Temperatur von 150°C emittierte. Ein weiterer Weg Nanopartikel zu stabilisieren, stellt der Einbau in makrokristalline Einkristalle durch Mischkristallbildung in Wasser oder organischen Lösungsmitteln dar. Die erhaltenen Kristalle zeichnen sich durch hohe photochemische und thermische Stabilität aus. Sie zeigen die Emissionseigenschaften der Nanopartikel, die nach Auflösung der Matrix wieder kolloidal in Lösung gehen. Allerdings liegen die Nanopartikel in der Kristallmatrix nicht regulär verteilt vor. Die Mischkristalle wurden erfolgreich als Luminophor in einer Gasentladungslampe und als Konversionsschicht einer kommerziellen LED getestet, die die Emission der Nanopartikel aufwies.

The aim of the thesis is to suggest a comprehensive and inexpensive method of diagnosing the solar cell quality via a conventional digital camera. The following questions are answered, Can a conventionaldigital camera be used for diagnosing the quality of solar cells?; If so,is the experimental setup for the quality diagnosing constrained to a laboratory and single solar cells or can it be done in a private home for a full-sized solar panel?; What are the defects that can be observed in this experiment? A conventional digital camera has been modified to acquire the electroluminescence (EL) images and dark thermography(RevEL) images. The experiment has been done in two locations with different types of samples. Multi-crystalline p-type single solar cells are used during the laboratory experiment. In the experiment set up at the private home, a conventional solar panel with 36 quadraturemulti crystalline silicon solar cells, that are equivalent to 9 full solarcells, is used. The EL imaging has been performed under the forward bias whereas the dark thermography imaging has been performed under reverse bias. The contrast in EL images is due to the radiativeand non-radiative recombination of injected excess minority charge carriers. A large non-radiative recombination site produces a large dark area in the EL image. Similarly, the contrast in RevEL images is due to the generation of charge carriers that are associated with the non-radiative recombination sites in the depletion layer. A large defect area produces a large bright area in the RevEL image. Hence,the EL image and the RevEL image are some what inverted images of each other. It is also found that the IV characteristics and the semi-log curves are in a good agreement with the EL and the RevEL images. When the EL image is combined with the hand-on devices like a mobile camera and a macro lens, it reveals defected areas like finger-interruptions, microcracks, grain boundaries and planar defects. Whereas the RevEL images, when combined with the image processing software tool, reveal the morphology of the defected sites. This justifies the beauty and the simplicity of using an every day digitalcamera as a diagnostic tool for the quality control of the solar cell

No description available.

No description available.

In dieser Arbeit wird ein grundlegender Rahmen für das Verständnis von photovoltaischer Ladungserzeugung an Grenzflächen zwischen einem Metalloxid und einem organischen Halbleiter geschaffen. Dabei wird gezeigt, dass hybride Ladungstransferzustände (HCTS) eine entscheidende Rolle im Energieumwandlungsprozess spielen. Vor ihrer endgültigen Trennung bleiben Elektronen und Löcher an gegenüberliegenden Seiten der Grenzfläche durch Coulomb-Interaktion aneinander gebunden. Nur wenn die Trennung eines solchen HCTS gelingt, kann es zu einem Photostrom beitragen. Die planaren Schichtsysteme ZnO/P3HT, ZnMgO/P3HT und SnO2/P3HT dienen als Modellsystem für eine ausführliche Studie über Energiestruktur der Grenzfläche, photovoltaische Energieumwandlung und die damit verbundenen Verluste. Es wird gezeigt, dass ein HCTS aus einem Elektron im Leitungsband des Metalloxids und einem Loch im HOMO des Polymers besteht. Folglich ist seine Entstehung eine intrinsische Eigenschaft von allen derartigen Grenzflächen. Elektrolumineszenzspektroskopie (EL) stellt sich als wirksame Methode zur Untersuchung von HCTS dar. Deren strahlende Rekombination produziert ein breites Signal im nahen Infrarotbereich. Spannungsabhängige EL-Messungen zeigen den hohen Grad an Delokalisierung von beiden Ladungsträgern in einem HCTS. EL-Spektren, die über einen weiten Temperaturbereich aufgenommen wurden, zeigen, dass nichtstrahlende Prozesse mit Abstand der dominierende Zerfallsmechanismus für HCTS bei Zimmertemperatur sind. Ein Modell aus mehreren Schritten für den Stromerzeugungsprozess kann aus temperaturabhängigen photovoltaischen Messungen abgeleitet werden. Hierbei wird deutlich, dass die Bindungsenergie von Elektron und Loch in einem HCTS keine bedeutende Einschränkung für die Leistungsfähigkeit einer Solarzelle darstellt. Die einflussreiche Rolle von nichtstrahlenden Zerfallsprozessen verursacht jedoch in allen untersuchten Materialsystemen schwere Verluste. / In this work, a fundamental framework for the understanding of photovoltaic charge generation at metal-oxide/organic hybrid interfaces is established. It is shown that hybrid charge transfer states (HCTS) play a crucial role in the power conversion process. Prior to full charge separation, pairs of electrons and holes situated at opposite sides of the heterojunction remain bound to each other by Coulomb interaction. Only if an HCTS is dissociated, a contribution to a photocurrent can be made. Planar heterojunctions of the material combinations ZnO/P3HT, ZnMgO/P3HT, and SnO2/P3HT serve as model systems for a broad investigation of interface energetics, photovoltaic power conversion and the loss processes therein. It is shown that an HCTS consists of an electron in the conduction band of the metal-oxide and a hole in the HOMO of the polymer. Consequently, its formation is an intrinsic property of all heterojunctions of that kind. Electroluminescence (EL) spectroscopy proves to be a powerful tool in the analysis of HCTS. Their radiative recombination produces a broad signal in the near-infrared spectral range. Voltage-dependent EL measurements reveal a high degree of delocalization of both carriers in an HCTS, whereas EL spectra recorded over a wide range of temperatures show that non-radiative processes are by far the dominant recombination channel for HCTS at room temperature. A multistep model of the charge generation process is derived from temperature-dependent photovoltaic measurements. It becomes apparent that the binding energy of electron and hole in an HCTS does not impose a significant limitation on device performance. The strong presence of non-radiative decay processes, however, causes severe losses for all material systems that are investigated in this work.

We demonstrate a new approach for fabricating alternating current driven organic electroluminescent devices using the concept of doping in organic semiconductors. Doped charge transport layers are used for generation of charge carriers within the device, hence eliminating the need for injecting charge carriers from external electrodes. The device is an organic-inorganic hybrid: We exploit the mechanical strength and chemical stability of inorganic semiconductors and combine it with better optical properties of organic materials whose emission color can be chemically tuned so that it covers the entire visible spectrum. The device consists of an organic electroluminescence (EL) layer composed of unipolar/ambipolar charge transport materials doped with organic dyes (10 wt% ) as well as molecularly doped charge generation layers enclosed between a pair of transparent insulating metal oxide layers. A transparent indium doped tin oxide (ITO) layer acts as bottom electrode for light outcoupling and Aluminium (Al) as top reflective electrode. The electrodes are for applying field across the device and to charge the device, instead of injection of charge carriers in case of direct current (DC) devices. Bright luminance of up to 5000 cd m-2 is observed when the device is driven with an alternating current (AC) bias. The luminance observed is attributed to charge carrier generation and recombination, leading to formation of excitons within the device, without injection of charge carriers through external electrodes.