In this thesis, we investigated charge carrier properties of two series of organic semiconductors with time of flight measurement. Charge carrier mobility is calculated in different electron filed and fitted to Poole-Frenkel model. In the first part, we investigated carrier properties of pyrrole derivatives .The mea- surement result of pyrrole derivatives with different functional group indicate that trans- port properties may effected by this different functional group and the bonding position. There have two different type of transport properties that is single transport and bipolar transport. In addition, carrier mobility have more than two order difference with this different functional group. Finally, we investigated carrier properties of anthracene derivatives. The measure- ment result indicate that the intermolecular aggregation can be solved by synthesizing another functional group to form polymer. This method not only perform excellent thin film stability but also keep bipolar transport property after synthesizing.

The effects of morphology on electronic and optical properties in solution processable photovoltaic (PV) materials have been studied through two different approaches. One approach, scanning photocurrent (PC) and photoluminescence (PL) microscopy, involved mapping PC generation and PL in functional PV devices on the length scale of around 250-500 nm. Additionally, local diode characteristics were studied from regions of interest in the PV through local voltage-dependent photocurrent (LVPC) measurements. In a PV made from a Copper Indium Gallium Selenide (CIGS) nanocrystal (NC) "ink", two morphological features were found to cause the spatial heterogeneity in PC generation. Cadmium Sulfide (CdS) aggregates lowered PC generation by blocking incident light to the photoactive layer, and cracks in the CIGS-NC film enhanced PC generation through improved charge carrier extraction. LVPC measurements showed all regions to have similar diode characteristics with the main difference being the PC generated at zero bias voltage. For another PV made from a donor/acceptor blend of poly(9,9-dioctylfluorene-co-bis-N,N-(4-butylphenyl)-bis-N,Nphenyl- 1,4-phenylenediamine (PFB) and poly(9,9-dioctylfluorene-co-benzothiadiazole)(F8BT), two incident laser wavelengths were used to selectively illuminate only one or both polymers. The results showed that when F8BT is illuminated, the PFB-rich regions produced the most PC and when both polymers are illuminated (but mostly PFB), the F8BT-rich regions produce the most PC; showing PC generation is more affective when less absorber material is present in the morphology. The other approach to study morphological effects on PV properties was to fabricate particles that mimicked morphological variations known to occur in solution-processable PVs. Through solution processing of an oligothiophene molecule, a range of weakly coupled H-aggregate particles were made. These particles, identifiable by shape, were shown to have a varying degree of energetic disorder (as gauged by the 0-0 vibronic band intensity in the emission spectrum), despite all particles showing a similarly high degree of molecular order from fluorescence dichroism (FD) measurements. A trend was observed correlating a decrease in energetic disorder with an increase in the local contact potential (LCP) difference as measured with Kelvin probe force microscopy (KPFM). The LCP difference was found to range by 70 mV between particles of moderate to low energetic disorder.

Since their experimental discovery in 2008, topological insulators have been catapulted to the forefront of condensed matter physics research owing to their potential to realize both exciting new technologies as well as novel electronic phases that are inaccessible in any other material class. Their exotic properties arise from a rare quantum organization of its electrons called ``topological order,'' which evades the conventional broken symmetry based-classification scheme used to categorize nearly every other state of ordered matter. Instead, topologically ordered phases are classified by topological invariants, which characterize the phase of an electron's wavefunction as it moves through momentum space. When a topologically ordered phase is interfaced with an ordinary phase, such as the vacuum, a novel metallic state appears at their shared boundary. In topological insulators, this results in the formation of a two-dimensional metallic state that spans all of its surfaces. The surface state electronic spectrum is characterized by a single linearly dispersing and helically spin-polarized Dirac cone that is robust against disorder. The helical nature of the surface Dirac cone is highly novel because the Dirac electrons carry a net magnetic moment and are capable of transporting 100% spin-polarized electrical currents, which are the long-sought electronic properties needed for many spin-based electronic applications. However, owing to the small bulk band gap and intrinsic electronic doping inherent to these materials, isolating the surface electronic response from the bulk has proven to be a major experimental obstacle. In this thesis, we demonstrate the means by which light can be used to isolate and study the surface electronic response of topological insulators using optoelectronic and nonlinear optical techniques. In chapter 1, we overview the physics of topological order and topological insulators. In chapter 2, we show how polarized light can be used to generate and control surface electrical currents that originate from the helical Dirac cone. In chapter 3, we demonstrate that the nonlinear second harmonic generation of light from a topological insulator is a sensitive surface probe and can be used to detect the breaking of space-time symmetries and monitor changes in the surface carrier density. / Physics

Indium-tin oxide (ITO) is commonly used as the transparent electrode in organic photovoltaic (OPV) devices. ITO's transparent properties come at the expense of less than ideal electrode characteristics arising from insulating over-oxidized surface species. OPVs fabricated on the native ITO surface tend to exhibit poor performance with a high degree of variability from device to device. Aggressive acid etching of the ITO surface removes the majority of the insulating surface species leading to improvements in OPV efficiency with greater reproducibility and increased device to device consistency.Organic light emitting diodes (OLEDs) are planar electroluminescent light sources that naturally couple a portion of their emission into internally reflected modes within the device substrate. Although this coupling property is well known, few attempts have been made to integrate OLEDs as light sources for internal reflection elements. Furthermore, OPVs share the optical coupling properties of OLEDs and therefore can be used as integrated internal reflection detectors. Integrating both an OLED light source and an OPV detector onto the same substrate results in an internal reflection sensing platform that requires no free-space optics, has low power consumption requirements, and can be easily fabricated on substrates occupying an area less than one square inch. In this work we establish a functional prototype design, characterize the fundamental coupling properties, and demonstrate several surface sensing responses of this fully integrated optical sensing platform.The net solar power production from OPVs arises from the interactions between multiple currents through the device. The photocurrent is the only power producing current in the device and understanding the voltage dependent nature of this current is essential in OPV research. Analysis methods of conventional, inorganic photovoltaics do not adequately describe the photocurrent behavior commonly observed in OPVs. OPV analysis is therefore somewhat limited by the methods commonly employed. To improve upon the convention methods we develop a simplified method of OPV photocurrent analysis based on electrochemical methods that accurately describes the voltage dependence of the photocurrent and leads to greater insight into the key parameters involved in solar power production from OPVs.

The emergence of complex, carefully designed, molecular architectures incorporating either a lanthanide ion or the porphyrinic macrocycle have stimulated significant interest of late, particularly in the fields of molecular switches, molecular machines and data storage systems. The integration of these emissive species has been shown to permit the analysis of conformational, coordinative, or electronic change, and employed, in the case of the porphyrinic macrocycle, to acquire a deeper understanding of the natural process of photosynthesis, thus opening up the possibility of developing more efficient and inexpensive photovoltaic cells. This thesis begins by providing insight into the generation of cathodic photocurrent density within both monophasic and biphasic self-assembled monolayers, before documenting how the magnitude of such photoelectochemical output can be gated upon the integration of an electron relay moiety, both at the interface and into solution. The introduction of an electron relay moiety into solution has been shown to bring about increases of up to 283 % in the magnitude of the cathodic photocurrent density acquired, whilst optimisation of the distances between the metallic interface, the electron relay moiety and the porphyrinic macrocycle has also proven beneficial. Greatest photoelectrochemical output (5.1 x 1014 nA mol-1 cm-2) is realised when the porphyrinic macrocycle is covalently tethered at a distance of 4.6 nm from the quenching, metallic interface, and the relay moiety integrated at a distance of 1.7 nm from the interface and 2.9 nm from the porphyrinic macrocycle, respectively. However, greatest variation (94 %) in the magnitude of the cathodic photocurrent densities acquired is observed when the distance between the porphyrinic macrocycle and the gold surface is kept at 3.3 nm, and the relay moiety situated at either 1.2 nm or 1.7 nm from the interface, respectively. Research then moved towards trying to integrate this established conformational ruler within a porphyrin-appended, bistable [2]rotaxane. Its implementation served to try to ensure that photoelectrochemical differentiation of the ground state coconformation (GSCC) and the metastable state co-conformations (MSCC) was viable, thus enabling the efficient resolution of anion-induced molecular motion within a dynamic supramolecular architecture by means of a novel approach. The focus of this thesis then shifts to the assembly of novel, optically switchable, ternary complexes exhibiting charge-transfer based on the donor-acceptor interaction between an electron-rich naphthalene derivative (EuNap) and MV2+, an electron-poor, redox-addressable moiety. Prior to the deposition of (MV, EuNap)-CB[8] at the interface, the homoternary analogue ((MV+.)2-CB[8]) was acquired upon one electron reduction of (MV, EuNap)-CB[8] in the presence of excess MV2+. This process was revealed to be reversible upon the application of a stream of oxygen, and the relative concentration of each complex present in solution quantified upon mathematical manipulation of the biexponential decay curve acquired; upon the addition of sodium thiosulfate (Na2S2O3), the percentage of uncomplexed EuNap (τ = 0.60 ms cf. τ = 0.1 ms (MV, EuNap)-CB[8]) present in solution increased in accordance with the generation of ((MV+.)2-CB[8]) and loss of the charge-transfer interaction (λmax = 390, 490 nm), of which has been shown to quench lanthanide luminescence (Eu3+, Yb3+, Nd3+). Thus, the assembly of a molecular switch is documented which may be followed qualitatively at higher concentration by a visible colour change, and at low concentrations quantitatively by virtue of luminescence spectroscopy. No optical output (λex = 227 nm, λem = 616 nm) was acquired upon the deposition of (MV, EuNap)CB[8]) due to the occurrence of surface energy transfer (SET). As a result, 1-(10-mercaptodecyl)-1'methyl-[4,4'-bipyridine]-diium bromide and 1-methyl-1'-(10-(naphthalen-2yloxy)decyl)-[4,4'bipyridine]-1,1'-diium bromide iodide were synthesised and the assembly of a molecular film envisaged in which the molecular recognition properties of CB[n] were maintained and significant optical output from the lanthanide ion (Eu3+, λem 616 nm) detected; the assembly of such a film centred on the formation of 1:2 intermolecular heteroternary complexes and the recruitment of EuNap at a distance ≥ 3.2 nm from the gold substrate. It was envisaged that the modulation of any emissive output would be brought about upon manipulating the oxidation state of a surface-confined metallocene. This thesis ends by summarising the research conducted and assessing how the inclusion chemistry of cucurbit[8]uril and the photophysical properties of the porphyrinic macrocycle can be combined in order to fabricate a dynamic, photoresponsive molecular assembly. The electrical energy generated from the efficient harvesting of light energy could be used in a multitude of applications, most notably as a nanoscale power supply to drive and control molecular and supramolecular actuations.

Modern studies on charge transfer reaction and conductivity measurements of DNA have shown that the electrical behavior of DNA ranges from that of an insulator to that of a wide bandgap semiconductor. Based on this property of DNA, a metal-semiconductor-metal photodetector is fabricated using a self-assembled layer of deoxyguanosine derivative (DNA base) deposited between gold electrodes. The electrodes are lithographically designed on a GaN substrate separated by a distance L (50nm < L < 100nm). This work examines the electrical and optical properties of such wide-bandgap semiconductor based biomaterial systems for their potential application as photodetectors in the UV region wherein most of the biological agents emit. The objective of this study was to develop a biomolecular electronic device and design an experimental setup for electrical and optical characterization of a novel hybrid molecular optoelectronic material system. AFM results proved the usage of Ga-Polar substrate in conjugation with DG molecules to be used as a potential electronic based sensor. A two-terminal nanoscale biomolectronic diode has been fabricated showing efficient rectification ratio. A nanoscale integrated ultraviolet photodetector (of dimensions less than 100 nm) has been fabricated with a cut-off wavelength at ~ 320 nm.

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