Optoelectronic characterisation techniques are assessed in their application to three solar cell systems. Charge injection barriers are found in PbS/ZnO colloidal quantum dot solar cells through the use of temperature dependent current-voltage and capacitance-voltage measurements. The injection barriers are shown to complicate the Mott-Schottky capacitance analysis which determines built-in bias and doping density. A model that incorporates depletion capacitance and a constant capacitance arising from the injection barriers is given to explain the Mott-Schottky plots. The junction mechanism at the PbS/ZnO interface is found to transition from excitonic to p-n behaviour based on the amount of UV photodoping the cell has received. External quantum efficiency analysis at different photodoping times reveals a growing charge collection region within the material, demonstrating the shift to p-n behaviour. This is further supported by the observance of depletion capacitance behaviour after, but not before, UV photodoping. Defects within GaAs cells containing InAs quantum dots are found to enhance the sub-bandgap performance of the cell using external quantum efficiency analysis. This is verified by illuminated current-voltage analysis using a 1000 nm high pass optical filter to block photons of larger energy than the bandgap. Using capacitance-voltage analysis, high temperature rapid thermal annealing is shown to induce defects in dilute nitride cells, which explains the drop in open circuit voltage compared to lower temperature annealed cells. The doping level of polymer solar cells exposed to air is found to increase with continued exposure using Mott-Schottky capacitance analysis. Current-voltage measurements show the formation of an Al2O3 barrier layer at the polymer/aluminium interface. The usefulness of capacitance-voltage measurements to probe the polymer/fullerene interface is investigated in thermally evaporated thiophene/C60 cells.

In recent years, the confocal and two photon microscopes have become ubiquitous tools in life science laboratories. The reason for this is that both these systems can acquire three dimensional image data from biological specimens. Specifically, this is done by acquiring a series of two-dimensional images from a set of equally spaced planes within the specimen. The resulting image stack can be manipulated and displayed on a computer to reveal a wealth of information. These systems can also be used in time lapse studies to monitor the dynamical behaviour of specimens by recording a number of image stacks at a sequence of time points. The time resolution in this situation is, however, limited by the maximum speed at which each constituent image stack can be acquired. Various techniques have emerged to speed up image acquisition and in most practical implementations a single, in-focus, image can be acquired very quickly. However, the real bottleneck in three dimensional imaging is the process of refocusing the system to image different planes. This is commonly done by physically changing the distance between the specimen and imaging lens, which is a relatively slow process. It is clear with the ever-increasing need to image biologically relevant specimens quickly that the speed limitation imposed by the refocusing process must be overcome. This thesis concerns the acquisition of data from a range of specimen depths without requiring the specimen to be moved. A new technique is demonstrated for two photon microscopy that enables data from a whole range of specimen depths to be acquired simultaneously so that a single two dimensional scan records extended depth of field image data directly. This circumvents the need to acquire a full three dimensional image stack and hence leads to a significant improvement in the temporal resolution for acquiring such data by more than an order of magnitude. In the remainder of this thesis, a new microscope architecture is presented that enables scanning to be carried out in three dimensions at high speed without moving the objective lens or specimen. Aberrations introduced by the objective lens are compensated by the introduction of an equal and opposite aberration with a second lens within the system enabling diffraction limited performance over a large range of specimen depths. Focusing is achieved by moving a very small mirror, allowing axial scan rates of several kHz; an improvement of some two orders of magnitude. This approach is extremely general and can be applied to any form of optical microscope with the very great advantage that the specimen is not disturbed. This technique is developed theoretically and experimental results are shown that demonstrate its potential application to a broad range of sectioning methods in microscopy.

The Pi-cell is known to have the fastest response time amongst commercialised nematic LCD applications due to the bend configuration. The Bend configuration can be obtained when a high voltage is applied to a Pi-cell initially treated to have a splay configuration, but transition is complex because the splay and the bend states are topologically not identical. Although two possible mechanisms (anchoring breaking and order reconstruction) can explain the bend transition, it is still difficult to be certain of the mechanism in some cases. In this thesis, therefore, the bend transition mechanism in the Pi-cell is investigated. Whichever mechanism is present, the bend transition speed is expected to increase when a high voltage is applied to the cell. However, in some cases, the application of a higher voltage reduces the bend transition speed. These phenomena are discussed based on various experimental results, and the reasons are also discussed. Four different regimes are suggested depending on the bend transition speed change. From these results, it is possible to understand the best way to obtain the bend state quickly in a TFT-LCD in the Pi-cell mode. During the experiments, unexpected light leakage was observed in the extinction position. It was proved that the light leakage came from the residual twist angle caused by the manufacturing process. In addition, two new methods were suggested for measuring the residual twist angle from the light leakage. One of the methods, the analytic method, was extended to the TN-cell. Allowing for the residual twist angle in the Pi-cell, the reason for lower CR compared to other LCD modes is discussed, and methods are suggested in this thesis to improve the CR of Pi-cell devices.

In my diploma thesis, there was created the summary of solar construcion, toys and another elements, which are available on the market. At first some construction were selected, than there were the experiments were drawn up and at the end the experiments were done by students dutiny the lessons.There is also a short movie including these experiment. The diploma thesis contains my own design of solar construction, the description of its manufactory and its use in teaching physics. There is also the description of accompanying website. On this website i tis possible to download the wokrsheets. These worksheets were tested dutiny the teaching and later than at work evalueted.

La structure traditionnelle d'un oscillateur optoélectronique (OEO) s'appuie sur une boucle de fibre optique très longue, servant de ligne à retard et lui conférant la grande pureté spectrale, ou le très faible bruit de phase de l'oscillateur. Un tel oscillateur fonctionnant à la fréquence de 8 GHz a été mis en œuvre aux laboratoires SATIE/LPQM de l'ENS Cachan. Néanmoins un tel système présente des inconvénients comme les dimensions un peu grandes, la difficulté de contrôler la température et un large peigne de fréquences parmi lequel il est difficile d'extraire un seule mode. Il est en fait possible d'éliminer ses inconvénients en remplaçant la boucle de fibre par un micro-résonateur optique de grand facteur de qualité. Dans cette thèse deux types résonateurs ont été fabriqués et étudiés. Des microsphères ont été fabriquées à partir de fibres optiques de fibres optiques monomodes. Les modes de galeries de ces résonateurs sont caractérisés grâce à couplage avec une fibre effilée. L'étude expérimentale met en évidence un facteur de qualité pouvant atteindre une valeur de 106 et un intervalle spectral libre (FSR) dépendant du diamètre de la sphère. Ainsi pour un diamètre de 300 µm on obtient un FSR de 0,2 nm soit 25 GHz en fréquence. Mais pour un OEO fonctionnant à la fréquence de 8 GHz il faudrait un FSR plus petit et donc une sphère dont le diamètre serait de taille millimétrique, donc très difficile à fabriquer. Un autre type de résonateur, en forme d'hippodrome, a été conçu et étudié. L'étude expérimentale a été conduite par un couplage avec de fibres lentillées. Le spectre en transmission présente des pics de résonances avec un facteur de qualité moyen de 0,050 ± 0.003 nm (correspondant en fait à 6 GHz) sur une plage de longueurs d'onde allant de 1534 nm à 1610 nm. Les caractéristiques les plus intéressantes de ce résonateur en forme d'hippodrome sont un facteur de qualité élevé et un intervalle spectral libre tout à fait en accord avec les besoins de l'OEO étudié. Néanmoins le couplage avec les fibres lentillées induit des pertes optiques trop importantes pour satisfaire aux conditions d'oscillations. Les travaux futurs devront porter sur l'amélioration du couplage ainsi que sur l'asservissement des pics de résonnance du micro-résonateur sur la longueur d'onde du laser employé dans l'OEO. / The classical structure of an Opto-Electronic Oscillator (OEO) is based on a long fiber loop acting as a delay line and leading to the high spectral purity, or very low phase noise, of the oscillator. Such an OEO has been developed in SATIE/LPQM laboratory at ENS Cachan, operating at 8 GHz frequency. However, this system has some main disadvantages such as a bulky size, the difficulty to control temperature and a wide range of peaks among which it is difficult to select only one mode. In order to eliminate these disadvantages, high quality factor optical resonator can be used instead of the optical fiber loop. In this thesis, two resonator structures are produced and investigated. Microspheres are fabricated based on optical single mode fiber. Whispering gallery modes of these resonators are characterized by tapered fiber –resonator coupling. The experimental results show that the quality factor of the microsphere is up to 106 and FSR depends on the diameter of the resonator. A microsphere with a diameter of 300 µm, presents a FSR of 0.2 nm corresponding to a frequency of 25 GHz. However, for an OEO system which should work at 8 GHz, microsphere with a smaller FSR or with diameter of some millimeters should be fabricated- that is really difficult to obtain. Another add/drop racetrack resonator is designed and investigated. Optical experimental behavior of racetrack is characterized via fiber micro-lens coupling. The transmission spectrum shows resonance dips with average quality factor of 105 and a small FSR of 0.050 ± 0.003 nm (actually corresponding to 6 GHz) for a scanning wavelength range from 1534 nm to 1610 nm. The most promising features of the racetrack resonator are its high quality factor, and its free spectral range, which give it the high suitability for being used in the OEO system. Nevertheless the coupling with fiber lens leads to high losses and it is not possible to fulfill the oscillation conditions. Future work should be conducted for improving the coupling and for controlling the resonance dips position in agreement with the wavelength of the laser used in the OEO.

Free-space optics (FSO), or wireless optical communications, has received extensive research due to its promise of practically limitless bandwidths. However, FSO has challenges yet to be met for a cost effective realisation. This D.Phil thesis explores a solution using a ferro-electric liquid crystal spatial light modulator (FLC SLM) and binary phase holograms to significantly reduce the hardware complexity of an FSO system with auto-alignment and turbulence compensation. The theory of binary phase hologram is presented and extended to obtain a new algorithm that is suitable for a FLC SLM. The algorithm is able to be used in a demonstration system to broadcast data streams to multiple receivers, showing the capability of using FLC SLM to form any beam configuration. An FSO transmitter is then developed that uses retro-reflectors as markers for the receivers. The transmitter combines an imaging system with the FLC SLM as a reconfigurable beam steering system for acquiring the retro-reflector location. The FLC SLM is also used to reduce aberrations in the optics, resulting in a significant increase in the transmitted beam power density. The accuracy of the acquisition is measured to give a small steering error without the use of a closed loop controller. An optical turbulence simulator, using the principals of binary phase hologram, is constructed to simulate optical beam propagation in turbulent conditions. The simulator accurately produces aberrations that have the same statistics with the theoretical prediction. Analysis of the phase distortion due to turbulence is performed and a wavefront sensorless turbulence compensation method based on the FLC SLM gives significant reduction in calculated bit error rates. New scintillation index derivation for multiple optical beams is described and then used to demonstrate further decrease in bit error rates.

Les propriétés intrinsèques extraordinaires de ces matériaux de faible dimension dépendent fortement de l'environnement auquel ils sont soumis. Par conséquent, ils doivent être préparés, traités et caractérisés sans défauts. Dans cette thèse, je discute de la manière de contrôler l'environnement des nanomatériaux de faible dimension tels que le graphène, le MoS$_{2}$ et les nanotubes de carbone afin de préserver leurs propriétés physiques intrinsèques. De nouvelles solutions pour l'amélioration des propriétés sont discutées en profondeur. Dans la première partie, nous fabriquons des dispositifs d'hétérostructure à base de graphène de Van der Waals (VdW) de dernière génération, en contact avec les bords, encapsulés dans du nitrure de bore hexagonal (hBN), afin d'obtenir un transport balistique. Nous utilisons une technique basée sur des mesures de bruit 1 / f pour sonder le transport de masse et de bord lors de régimes Quantum Hall entiers et fractionnaires. Dans la deuxième partie, le même concept de fabrication des hétérostructures VdW a été étendu pour encapsuler la couche monocouche MoS $_{2}$ dans le hBN afin d'en modifier les propriétés optiques. À cet égard, nous présentons une étude approfondie sur l'origine et la caractérisation des défauts intrinsèques et extrinsèques et leur incidence sur les propriétés optiques. En outre, nous décrivons une technique pour sonder le couplage entre couches ainsi que la génération de lumière avec une résolution spatiale inférieure à la limite de diffraction de la lumière. Enfin, nous discutons d'un processus systémique naturel visant à améliorer les propriétés mécaniques de la soie polymérique naturelle à l'aide d'une nanotubes de carbone à paroi unique fabriqués par HipCO comme aliment pour le ver à soie. / The extraordinary intrinsic properties of low dimensional materials depend highly on the environment they are subjected to. Hence they need to be prepared, processed and characterized without defects. In this thesis, I discuss about how to control the environment of low dimensional nanomaterials such as graphene, MoS2 and carbon nanotubes to preserve their intrinsic physical properties. Novel solutions for property enhancements are discussed in depth. In the first part, we fabricate state-of-the-art, edge-contacted, graphene Van der Waals(VdW) heterostructuredevices encapsulated in hexagonal-boron nitride(hBN), to obtain ballistic transport. We use a technique based on 1/f-noise measurements to probe bulk and edge transport during integer and fractional Quantum Hall regimes. In the second part, the same fabrication concept of VdW heterostructures has been extended to encapsulate monolayer MoS2 in hBN to improve optical properties. In this regard we present an extensive study about the origin and characterization of intrinsic and extrinsic defects and their affect on optical properties. Further, we describe a technique to probe the interlayer coupling along with the generation of light with spatialresolution below the diffraction limit of light. Finally, we discuss a natural systemic process to enhance the mechanical properties of natural polymer silk using HipCO-made single walled carbon nanotubes as a food for silkworm.

Dès à présent, le monde est face à des enjeux majeurs : augmentation de la production d'énergie, réduction des impacts de la production et de la consommation d'énergie sur l'environnement. La transition vers des énergies durables a déjà commencé. Le photovoltaïque a sa place parmi les énergies renouvelables qui permettront de relever ce défi. Ce travail de thèse porte sur les pérovskites hybrides halogénées et plus particulièrement leur utilisation dans des cellules solaires. En effet très récemment, ces matériaux ont attiré l'attention de la communauté scientifique en raison de leurs propriétés optoélectroniques remarquables : bande interdite directe, forte absorption de la lumière, longueurs importantes de diffusion des porteurs, propriétés optoélectroniques accordables mais aussi une fabrication aisée et à bas coût. En quelques années, le rendement a connu une augmentation spectaculaire de 3,8 % en 2009 à 22,7 % en 2017. Ainsi, ces derniers résultats placent les cellules pérovskites comme des concurrents potentiels face aux cellules solaires à base de silicium cristallin qui représentent aujourd'hui 90 % des cellules en service. Dans la conception des cellules solaires à base de pérovskite, la couche de pérovskite est généralement intercalée entre deux couches de transporteurs de charges : les couches de transporteurs d'électron et de trou (ETM et HTM, respectivement). La qualité de ces couches est essentielle pour obtenir de hauts rendements. Dans ce travail, les propriétés optoélectroniques des pérovskites halogénées sont étudiées ainsi que plusieurs couches de transport de charge. / In the future, the world has to face up to major challenges: increasing the energy production, reducing the environmental impact, moving towards sustainability in energy, etc. Renewable energies such as photovoltaics can meet these challenges. This thesis concerns hybrid halide perovskite materials and their use in solar cells. These materials have recently attracted a lot of attention owing to their direct bandgaps, strong light absorption, large carrier diffusion lengths, tunable optoelectronic properties, and their facile and low-cost fabrication In few years, their energy conversion efficiency has rapidly increased from 3.8 % in 2009 to 22.7 % in 2017, hence approaching efficiencies of crystalline silicon based-devices which represent 90% of commercial photovoltaic cells. In the design of perovskite cells, the perovskite photoabsorber is generally sandwiched by two interfacial layers that yield selective charge collections: the hole and electron transport layers (HTM and ETM). Good quality and adapted interfacial layers are required to obtained high efficiency cells. In this thesis, both the perovskite material and the interfacial layers are investigated.

Solar cells and photodetectors rely on similar physical principles based on the interaction of light and matter. Both types of optoelectronic devices are indispensable in a wide range of technological applications, from large-scale renewable power conversion to everyday consumer items. In this thesis, the use of facile solution-processable semiconductors in solar cells and light sensors is studied with a focus on antimony sulfide (Sb₂S₃) and antimony sulfoiodide (SbSI). The improvement of the photovoltaic performance in Sb₂S₃ sensitized solar cells upon the controlled partial oxidation of the absorber layer is investigated. A reduction in charge carrier recombination is the reason for the improved efficiency, caused by the oxidation process. Further, a new chemical bath deposition method for antimony sulfide is developed. Carried out at room temperature, this technique eliminates the necessity of cooling equipment during the deposition process. The antimony sulfide from this method decreases the density of trap states compared to the conventional deposition. Power-conversion efficiencies of up to η=5.1% are achieved in antimony sulfide sensitised solar cells using the new room temperature deposition method. Finally, antimony sulfide is used as a precursor to form films of antimony sulfoiodide (SbSI) micro-crystals in a facile physical vapour process. These films are then used to fabricate photodetectors. With PMMA as an insulating spacer layer, the devices are built in a sandwich-type architecture. Optoelectronic characterisation shows that these devices have the shortest response and recovery times reported for SbSI photodetectors to date.

Atomically thin two-dimensional nanomaterials such as graphene and transition metal dichalcogenides (TMDCs) have seen a rapid growth of exploration since the isolation of monolayer graphene. These materials provide a rich field of study for physics and optoelectronics applications. Many applications seek to combine a two dimensional (2D) material with another nanomaterial, either another two dimensional material or a zero (0D) or one dimensional (1D) material. The work in this thesis explores the consequences of these interactions from 0D to 2D. We begin in Chapter 2 with a study of energy transfer at 0D-2D interfaces with quantum dots and graphene. In our work we seek to maximize the rate of energy transfer by reducing the distance between the materials. We observe an interplay with the distance-dependence and surface effects from our halogen terminated quantum dots that affect our observed energy transfer. In Chapter 3 we study supercapacitance in composite graphene oxide- carbon nanotube electrodes. At this 2D-1D interface we observe a compounding effect between graphene oxide and carbon nanotubes. Carbon nanotubes increase the accessible surface area of the supercapacitors and improve conductivity by forming a conductive pathway through electrodes. In Chapter 4 we investigate effective means of improving sample quality in TMDCs and discover the importance of the monolayer interface. We observe a drastic improvement in photoluminescence when encapsulating our TMDCs with Boron Nitride. We measure spectral linewidths approaching the intrinsic limit due to this 2D-2D interface. We also effectively reduce excess charge and thus the trion-exciton ratio in our samples through substrate surface passivation. In Chapter 5 we briefly discuss our investigations on chemical doping, heterostructures and interlayer decoupling in ReS₂. We observe an increase in intensity for p-doped MoS₂ samples. We investigated the charge transfer exciton previously identified in heterostructures. Spectral observation of this interlayer exciton remained elusive in our work but provided the motivation for our work in Chapter 4. We also discuss our preliminary results on interlayer decoupling in ReS₂.