Charge transfer efficiency at the organic/transparent conducting oxide (TCO) interface is one of the key parameters controlling the overall efficiency of organic photovoltaics (OPVs). Modification of this interface with a redox-active organic surface modifier may further enhance the charge transfer across the interface by providing a charge-transfer pathway between the electrode and the organic active layer. Functionalized perylene diimide molecules (PDI) are useful for modifying metal oxide/acceptor interfaces for inverted solar cell devices because their LUMO energy level is close to some commonly used acceptor molecules. The effects of PDI structural parameters on the interfacial charge transfer processes across the organic/ITO interface were investigated. Six different PDI monolayers with different structural parameters were deposited on ITO surfaces to investigate the relationship between molecular orientation, linker length, aggregation and charge transfer process. The PDI orientation, degree of PDI aggregation and charge transfer process acrosses PDI/ITO interfaces were characterized by polarized ATR spectroscopy, PM-ATR spectroscopy and photoelectrochemistry. Both linker length and orientation affected the tunneling distance between PDI and ITO, therefore affecting the charge transfer rate constant across the PDI/ITO interfaces. PDI aggregation forced a more out-of-plane orientation of PDI molecules and increased the overall measured charge transfer rate constant. However, PDI aggregation also increased the excited state recombination rate which ultimately led to decrease of the charge collection efficiency. The first application of a PM-TIRF platform to characterize the electron-transfer processes of PDI monomeric films across the organic/electrode interface is presented. The PM-TIRF technique provides higher sensitivity as well as the capability to measure very fast charge transfer events, compared to other commonly used potential-modulated spectroscopy techniques. PDI-phenyl-PA monomeric films exhibited a more in-plane orientation compared with aggregated films and showed a smaller charge transfer rate constant across the PDI/ITO interfaces compared with PDI films with higher degrees of aggregation after normalizing the tunneling distance contributions.

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

A dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of requirements for the degree of Master of Science. Johannesburg, 2015. / Organic Photovoltaic (OPVs) is a promising alternative technology to provide clean and inexhaustible energy due to their excellent optoelectronic properties of the active polymer blends. The organic polymers have low weight, tunable electrical and optical properties besides being relatively insensitive to film imperfections which in the long run enable low-cost high-throughput roll-to-roll processing. However, their photo-conversion efficiency (PCE) and instability to air remains their greatest drawback as these preclude their commercialization. Indeed the highest power-conversion efficiency reported in literature is between 10-12 % compared to their inorganic counterparts (40 %). Therefore there is great need for improvement to make them competitive with grid parity. In this thesis, the major factors limiting the efficiency of organic solar cells such as light absorption, exciton diffusion and dissociation as well as charge collection are investigated and discussed. Despite the high thickness dependent absorption coefficients (>105 cm-1) within the visible spectrum the materials exhibit short exciton diffusion lengths (10-20 nm) which limit the optimal active layer thickness to a few nanometers. Improving optical absorption within this thickness forms the basis of this project. We report the use of surface Plasmons synthesized by both thermal evaporation and Radio Frequency (RF) magnetron sputtering system to tune and enhance optical absorption and scattering using the surface Plasmon resonance effect. The NPs were annealed at various temperatures and for different times to reconstruct and modify their shapes, sizes as well as the inter-particle distance (coverage). Stability is of paramount importance in organic semiconductor devices. Serious degradation in air constrains their applications potential. The study further investigates the mechanisms that determine the stability of organic photovoltaic devices. Our results depict the degradation mechanisms and their circumvention through the use of high mobility pentacene to improve stability.

Neste trabalho, nós estudamos as propriedades ópticas de absorção e emissão de polímeros conjugados luminescentes baseados no poli(p-fenileno de vinilideno) (PPV). Este material foi processado na forma de filme pelas técnicas casting, spin-coating, self-assembled (SA) e Langmuir-Blodgett (LB), disponíveis no Grupo de Polímeros Bernhard Gross, e caracterizado opticamente e quimicamente As propriedades ópticas do PPV foram investigadas através das seguintes técnicas: fotoluminescência (PL), fotoluminescência por excitação seletiva e absorção óptica. As medidas foram realizadas em função da temperatura da amostra e polarização luz de excitação e emissão. A caracterização química e estrutural do material estudado foi feita através de espectroscopia de infravermelho e analise de elementos. A anisotropia molecular no plano de filmes LB-PPV foi estudada por dicroísmo circular e medidas de birrefringência. Uma nova metodologia do material usado e de preparação de filmes de PPV também foi desenvolvida neste trabalho. Nós adotamos uma rota alternativa que consiste na substituição do contra-íon do precursor, poli(cloreto de tetrahidrotiofeno de xililideno) (PTHT), em solução aquosa por um íon de cadeia longa, o sal de sódio do ácido dodecilbenzenosulfonico (DBS). A vantagem da utilização deste polímero precursor está na possibilidade de converter filmes de PPV com alto grau de conjugação a 115 °C em apenas 3 minutos. Usando o DBS, os filmes de PPV podem ser convertidos sobre atmosfera ambiente e temperaturas de 80 °C, com propriedades ópticas melhores que as obtidas pelos métodos convencionais de conversão de filmes a temperaturas acima de 200 °C sobre vácuo. Filmes estáveis de Langmuir de PTHT-DBS foram transferidas sobre substratos de quartzo. Os filmes LB-PPV apresentaram uma grande anisotropia, demonstrada pelos experimentes de dicroísmo linear observados por absorção óptica e emissão de luz linearmente polarizada e por medidas de birrefringência. Além do mais, filmes SA-PPV foram produzidos por uma metodologia diferente. A adsorção alternada das camadas de PTHT e DBS resulta em filmes de PPV com grande grau de conjugação e espectros com estrutura bem resolvida. Um grande aumento da PL causado pela luz de excitação, na presença de ar, foi observado em filmes de PPV. Este efeito é acompanhado por um deslocamento para o azul do espectro de absorção, resultado da diminuição do comprimento de conjugação efetivo e formação de defeitos estruturais como o grupo carbonila. O aumento da PL pode ser explicado considerando a difusão dos portadores de carga por transferência de energia de via Förster para a região não degradada do filme de PPV, este processo é ativado pela formação de um perfil energético ao longo do filme devido a uma distribuição de segmentos conjugados gerados por foto-oxidação. O modelo teórico baseado nos dados experimentais e considerando o parâmetro geométrico é proposto. Finalmente, a análise de linha espectral da absorção e emissão do PPV com diferentes graus de conjugação foi realizada com sucesso na região das transições eletrônicas entre os estados não localizados p-p* pela análise de Franck-Condon. / In this work, we studied the optical proprieties of absorption and emission of luminescent conjugated polymers based on poly(p-phenylene vinylene) (PPV). This material was processed in thin films by casting, spin-coating, self-assembled (SA) e Langmuir-Blodgett (LB) techniques, available in the Grupo de Polímeros Bernhard Gross, where the samples were characterized optically and chemically. The optical proprieties of PPV were investigated by the following techniques: photoluminescence (PL), photoluminescence excitation spectroscopy and optical absorption. The measurements were carried out in function of sample temperature and polarization of the excitation and the emission light. The chemical and structural characterization of the material was performed by infrared spectroscopy and elemental analysis. The molecular anisotropy in plane of LB-PPV films were studied by circular dichroism and birefringence experiments. A new methodology in the material and film processing was developed in this work. Here we have adopted an alternative approach consisting in substituting the chloride counter ion of a water-soluble precursor, poly(xylylidene tetrahydrothiophenium chloride) (PTHT), by a long chain sulfonic counter ion (DBS) using a sodium salt of dodecylbenzenesulfonic acid. The advantage of this precursor polymer lies in the possibility of converting PPV films with a high conjugation length at 115 °C within only 3 min. Using DBS allowed PPV films to be converted under atmospheric pressure at temperatures as low as 80 oC, with conjugation length and optical properties better than for standard films converted at temperatures above 200 oC under controlled atmospheres. Stable Langmuir PTHT-DBS monolayers were transferred onto quartz substrates in the form of LB films. These LB-PPV films are highly anisotropic as demonstrated by linear dichroism experiments using linearly polarized optical absorption and emission and by birefringence measurements. Furthermore, SA-PPV films were produced by a different methodology. The adsorption on alternate PTHT and DBS layers result in PPV films with high conjugation degree and well-resolved spectral structure. These results are not similar in the literature. A strong PL enhancement was observed in PPV films caused by light excitation in the presence of air. This effect is accompanied by a blue-shift in the absorption spectrum resulting in shortened effective conjugation length and by a formation of defects such as carbonyl groups. The PL enhancement can be explained by an efficient incoherent diffusion of excited carriers to non-degraded PPV segments by Förster transfer, which is activated by the formation of an energy profile in the film due to distribution conjugation lengths generated by photodegradation. A theoretical model based on experimental data and considering the geometric parameters is proposed. Finally, the spectral line shape of absorbance and emission of PPV with different conjugation degrees was analyzed with success in the region of p-p* non-localized electronic transitions by Franck-Condon analysis.

As the rapid development of the applications of unconventional semiconductors in the 21th century, the new electronic and bioengineering revolutions based on solid state devices have become possible, that is facilitated through the understanding of electron or energy transfer process at the functionalized interfaces of organic semiconductors and two-dimensional (2D) materials. Especially in applications of photovoltaics and biosensors, the attributes of the interfaces play an important role in performance advancement. In this thesis, I have focused on the utilization of organic small molecule semiconductors as energy cascade materials to modify the interfaces between donor and acceptor of P3HT/PC₆₁BM binary organic solar cell, so as to improve the device performance. The charge transfer process at the interface of P3HT and functionalized graphene has also been investigated through P3HT/functionalized graphene blending photovoltaic devices. Moreover, I have concentrated on the interface of single layer MoS₂ and fluorescently-labeled DNA, where the electrons were transferred from fluorescent groups of DNA to MoS₂, resulting in fluorescence quenching. This quenching characteristic can be useful in other related biosensors. / In Chapter 1, an introduction to organic semiconductors and two-dimensional materials for applications in photovoltaics and biosensors has been presented. In Chapter 2, the experimental details used in this thesis have been discussed. / In Chapter 3, a novel small organic semiconductor molecule (CPA) with ambipolar attribute as an energy cascade material has been employed, to fabricate bulk heterojucntion solar cells. The organic photovoltaic devices with ternary structures, demonstrates a step of energy cascade to assist charge transfer between the electron-donating P3HT and electron-accepting PC₆₁BM. The ternary structure offers a distinct platform and an easily applicable approach to overcome shortcomings in P3HT-PC₆₁BM system by increasing the attainable product of short circuit current (JSC) and open circuit voltage (VOC). This ternary structure also retains the simplicity of a single processing step for photoactive layer. / In Chapter 4, to explore the potential of the p-type small organic semiconductor DTDCTB as energy cascade material in ternary blend bulk heterojunction (BHJ) solar cells, I have studied a BHJ system based on poly (3-hexylthiophene) (P3HT), [6,6]-phenyl C₆₁ butyric acid methyl ester (PC₆₁BM) and DTDCTB. This ternary structure demonstrates the improvement of power conversion efficiency (PCE) as compared to that of the binary devices composed of P3HT/PC₆₁BM alone. A systematic spectroscopic study was carried out to elucidate the underlying mechanism. Wavelength-dependent external quantum efficiency measurement confirmed the DTDCTB contribution to the increased photocurrent. Photoinduced spectroscopy and transient photovoltage measurements unambiguously revealed that the charges generated in DTDCTB were efficiently transferred to and transported in P3HT and PC₆₁BM. The results also suggested that despite the realization of cascade charge transfer, the bimolecular charge recombination process in the ternary system is still dominated by the P3HT/PC₆₁BM interface. / In Chapter 5, a simple method by using aryl diazonium salt reaction has been devised to achieve covalent bond formation by altering the hybridization of carbon atom in configuration of sp² to sp³. Afterwards the group of benzoic acid has been grafted onto pristine graphene, to open a band gap of this two-dimensional material. It was well functionalized, dissolved in organic solvents to provide the various of fabrication processes for electron devices. The LUMO of functionalized graphene below the LUMO of P3HT and close to that of PC₆₁BM indicates its suitability as an electron-acceptor for OPV applications. Then the bulk heterojunction solar cells composed of P3HT/functionalized graphene composite as active layer have been further prepared, achieving a PCE efficiency of 1.1%. / In Chapter 6, a novel MoS₂-based fluorescent biosensor for DNA detections via hybridization chain reactions (HCRs) has been demonstrated. MoS₂, as an emerging nanomaterial, has excellent fluorescence quenching ability and distinct adsorption properties for single- and double-stranded DNA. In the sensing method, MoS₂ nanosheets were used to suppress the background signal and control the “on” and “off” states of fluorescence emission of the detection system with and without the presence of the target DNA. In addition, the signal generation was amplified through the target-triggered HCRs between two hairpin probes. The utilization of MoS₂ and HCRs guaranteed the high sensitivity of the detection strategy with the detection limit of 15pM. The biosensor also exhibited very good selectivity over mismatched DNA sequences. The detection took place in solutions and requires only one “mix-and-detect” step. The high sensitivity, selectivity, and operational simplicity demonstrate that MoS₂ can be a promising nanomaterial for versatile biosensing. / In Chapter 7, I provide the conclusions and a brief prospect of the further development in ternary system of perovskite solar cells and in based-two dimensional materials micro-fluidic biological monitoring FET. / 對於二十一世紀，隨著人們對非传统半导体材料应用的發展有著迫切的需求，新的基於固態器件的電子工程和生物工程的革命正在悄然進行，這是基於對有機半導體材料和二維層狀材料的功能化的界面上發生的電子或者能量轉移的理解，特別是在太陽能電池器件和生物傳感器方面上的應用。本論文主要是關注與利用有機半導體小分子作為能級梯級材料去调节P3HT/PC₆₁BM二元有機光伏器件中給體與受體見的界面，從而得到更好性能的器件。同時也關注了P3HT和功能化的石墨烯界面上的電荷轉移，并通過P3HT/功能化石墨烯混合有機光伏器件來研究界面上的電荷轉移。另外，還關注了單層硫化鉬和螢光標記的DNA間的界面，在這個界面上DNA螢光基團的能量會轉移到二硫化鉬上從而導致螢光淬滅，並且應用這一淬滅特性在生物傳感上。 / 在第一章中，本論文對有機半導體和二維材料在光伏器件和生物傳感器件中的應用給出了一個簡單的介紹。第二章展示了論文涉及到的檢測方法。 / 在第三章中，本論文利用一種新型的具有雙極性的有機半導體小分子(CPA)作為能級梯級材料去製作異質結太陽能器件。這些具有三元體系結構的太陽能器件展示了能級梯級變化的過程，這個過程是為了改善電子給體P3HT和電子受體PC₆₁BM間的電荷轉移。這種三元體系結構提供了一種顯著而且簡單的方法來克服P3HT-PC₆₁BM二元體系的不足，并通過提高其短路電流和開路電壓的乘積來實現，同時保持簡單的一步光敏層的製作方式。 / 在第四章中，為了探索P型有機半導體小分子DTDCTB能否作為級聯材料在有機異質結太陽能器件中使用，本論文研究了三元體系包含P3HT，PC₆₁BM和DTDCTB的有機異質結太陽能器件。這種三元結構器件展現出更佳的性能對比與P3HT/PC₆₁BM二元體系器件。另外，三元體系中電荷轉移的內在機制通過一系列系統的光譜來闡明。光誘導光譜和瞬態光電壓測試明確的揭示了DTDCTB中產生的電荷會被有效的通過P3HT和PC₆₁BM傳輸走。這些結果還表明，儘管存在級聯電荷傳輸，但是雙分子間的電荷複合過程主要發生在P3HT/PC₆₁BM界面。 / 第五章提出一個簡單的通過使用芳香基重氮鹽反應的方法，實現了碳碳共價鍵合成的反應，這種反應是通過改變碳原子sp²雜化成sp³雜化的方式進行的，而且可以移植苯甲酸官能團到原味的石墨烯上來打開石墨烯的帶隙。石墨烯這種二維層狀材料通過明確的的功能化后，可以溶在有機溶劑中從而提供了其作為電子器件的製作工藝的多元化。功能化后的石墨烯的LUMO能級比P3HT的LUMO能級要低，並且接近于PC₆₁BM的LUMO能級，這一特性意味著功能化后的石墨烯作為電子受體在有機光伏器件中的應用是可行的。因此，本論文進一步展示了以P3HT和功能化后的石墨烯複合材料作為光敏層的異質結太陽能器件，並且其具有1.1%的光電轉化效率。 / 在第六章中，本論文提出了一種新型基於二硫化鉬的螢光生物傳感器，這一傳感器通過雜交連鎖反應(HCRs)應用於DNA檢測。二硫化鉬作為新興的納米材料，有著對單鏈或者雙鏈DNA的良好螢光淬滅和顯著的吸附特性。在此檢測方法中，二硫化鉬納米片被用來抑制背景信號，並且通過存在或者不存在目標DNA來控制檢測體系中螢光發射的開啟和閉合。另外，檢測信號通過兩個髮夾型DNA探針間的目標觸發的HCR方法放大。通過使用二硫化鉬和HCR實現了高靈敏度的檢測，其檢測極限是15pM。這個傳感器對於DNA的錯配具有良好的選擇性。這個檢測在溶解中進行，並且僅僅需要簡單的一步混合來實現。高的靈敏度、選著性和工藝簡單等特性表明了二硫化鉬這種納米材料可以在多種生物檢測中使用。 / 第七章三元體系鈣鈦礦結構光伏器件和基於二維材料微流生物檢測器件的應用。 / Ye, Lei. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2014. / Includes bibliographical references. / Abstracts also in Chinese. / Title from PDF title page (viewed on 04, October, 2016). / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only.

Wong, Man Keung. / "November 2010." / Thesis (M.Phil.)--Chinese University of Hong Kong, 2011. / Includes bibliographical references. / Abstracts in English and Chinese. / Abstract --- p.i / Table of contents --- p.iii / List of Figures --- p.vi / List of Tables --- p.ix / Chapter Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Background --- p.1 / Chapter 1.2 --- History of organic photovoltaic cells --- p.2 / Chapter 1.2.1 --- Single layer organic photovoltaic cells --- p.2 / Chapter 1.2.2 --- Bilayer organic photovoltaic cells --- p.3 / Chapter 1.2.3 --- Bulk Heterojunction organic photovoltaic cells --- p.6 / Chapter 1.3 --- Device physics of organic photovoltaic cells --- p.9 / Chapter 1.4 --- Device fabrication and characterization --- p.12 / Chapter 1.5 --- Thesis outline --- p.14 / Chapter Chapter 2 --- Instrumentation --- p.18 / Chapter 2.1 --- Keithley 236 source measure unit --- p.18 / Chapter 2.2 --- CHI 660C electrochemical instrument --- p.18 / Chapter 2.3 --- Tensor Alpha Step 500 Profilometer --- p.19 / Chapter 2.4 --- Fourier Transform Infrared (FTIR) spectroscopy --- p.20 / Chapter 2.5 --- Thermogravimetric Analysis --- p.22 / Chapter 2.6 --- X-ray Diffraction --- p.23 / Chapter 2.7 --- Scanning electron microscopy --- p.24 / Chapter 2.8 --- Atomic force microscopy --- p.26 / Chapter Chapter 3 --- Surface functionalization of Carbon Nanotube --- p.28 / Chapter 3.1 --- Introduction --- p.28 / Chapter 3.2 --- Oxidative treatment --- p.28 / Chapter 3.2.1 --- Experimental procedures --- p.28 / Chapter 3.2.2 --- Characterization --- p.29 / Chapter 3.3 --- Hydrothermal treatment --- p.35 / Chapter 3.3.1 --- Experimental procedures --- p.35 / Chapter 3.3.1.1 --- Synthesis of MWCNTols --- p.35 / Chapter 3.3.1.2 --- Synthesis of MWCNT-PEDOT --- p.36 / Chapter 3.3.2 --- Characterization --- p.37 / Chapter 3.4 --- Summary --- p.42 / Chapter Chapter 4 --- P3HT/f-CNT/PCBM Composites for Organic Photovoltaic Cells --- p.45 / Chapter 4.1 --- Introduction --- p.45 / Chapter 4.2 --- Fabrication procedures --- p.48 / Chapter 4.3 --- IV characteristics of organic photovoltaic cells --- p.51 / Chapter Chapter 5 --- Vertically aligned poly(3-hexylthiophene) nanobrushes of high aspect ratio for photoelectrochemical solar cells --- p.60 / Chapter 5.1 --- Introduction --- p.60 / Chapter 5.2 --- Sample preparation --- p.63 / Chapter 5.3 --- IV characteristics of P3HT nanobrushes --- p.65 / Chapter 5.4 --- AFM and XRD analysis --- p.66 / Chapter 5.5 --- Summary --- p.71 / Chapter Chapter 6 --- Conclusions --- p.74 / Chapter 6.1 --- Conclusions --- p.74

Zhao, Wei. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2008. / Includes bibliographical references. / Abstracts in English and Chinese. / Acknowledgements --- p.v / Chapter Chapter 1 --- Introduction --- p.1 / Chapter Chapter 2. --- H-bonded Acenes- An Approach to Self- assembled Organic Semiconductors --- p.16 / Chapter 2.1 --- Introduction --- p.16 / Chapter 2.2 --- Result and discussion --- p.17 / Chapter 2.3 --- Experiment --- p.23 / Chapter Chapter 3. --- Transistors from a Conjugated Macrocycle Molecule: Field and Photo Effects --- p.30 / Chapter 3.1 --- Introduction --- p.30 / Chapter 3.2 --- Result and discussion --- p.31 / Chapter 3.3 --- Conclusion --- p.37 / Chapter 3.4 --- Experiment --- p.37 / Chapter Chapter 4 --- Synthesis of Soluble and liquid crystalline Conjugated Macrocylces --- p.48 / Chapter 4.1 --- Introduction --- p.48 / Chapter 4.2 --- Result and Discussion --- p.49 / Chapter 4.3 --- Conclusion --- p.54 / Chapter 4.4 --- Experiment --- p.55 / Appendix --- p.65

Wu, Chin Kong. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2009. / Includes bibliographical references (p. 122-131). / Abstract also in Chinese. / ABSTRACT (English) --- p.i / ABSTRACT (Chinese) --- p.iii / ACKNOWLEDGMENTS --- p.v / TABLE OF CONTENTS --- p.vi / Chapter CHAPTER 1 --- Introduction --- p.1 / Chapter 1.1 --- Organic light-emitting- diode (OLED) --- p.2 / Chapter 1.2 --- Organic photovoltaics --- p.5 / Chapter 1.3 --- Organic field-effect transistor --- p.10 / Chapter CHAPTER 2 --- Properties of organic semiconductor --- p.17 / Chapter 2.1 --- Organic semiconductors --- p.17 / Chapter 2.2 --- Electronic structure of organic semiconductors --- p.18 / Chapter 2.3 --- Disorder and traps in organic semiconductors --- p.19 / Chapter 2.4 --- Charge carriers transport in organic semiconductors --- p.20 / Chapter 2.4.1 --- Polaron model --- p.21 / Chapter 2.4.2 --- Scher-Montroll model --- p.21 / Chapter 2.4.3 --- Gaussian disorder model --- p.23 / Chapter 2.5 --- Metal/organic interfaces --- p.25 / Chapter CHAPTER 3 --- Experimental details --- p.28 / Chapter 3.1 --- Sample preparation --- p.28 / Chapter 3.1.1 --- Organic semiconductors used in this thesis --- p.28 / Chapter 3.1.2 --- Cleaning of substrate --- p.29 / Chapter 3.1.3 --- Deposition of organic layer --- p.29 / Chapter 3.1.4 --- Deposition of metal --- p.31 / Chapter 3.2 --- Electrical characterization methods --- p.32 / Chapter 3.2.1 --- Current density 一 voltage (J-V) measurement --- p.32 / Chapter 3.2.2 --- Dark Injection Space-Charge-Limited (DI-SCL) transient current measurement --- p.38 / Chapter 3.2.3 --- Temperature varied J-V measurement --- p.43 / Chapter 3.2.4 --- Admittance spectroscopy --- p.44 / Chapter CHAPTER 4 --- Charge transport properties in single-organic-layer devices --- p.51 / Chapter 4.1 --- Experimental scheme --- p.51 / Chapter 4.2 --- Experimental results and discussion --- p.53 / Chapter 4.2.1 --- J-V measurements --- p.53 / Chapter 4.2.1.1 --- MTDATA --- p.53 / Chapter 4.2.1.2 --- NPB --- p.59 / Chapter 4.2.2 --- DI-SCL transient current measurement --- p.64 / Chapter 4.2.3 --- Admittance spectroscopy --- p.68 / Chapter 4.2.3.1 --- MTDATA --- p.68 / Chapter 4.2.3.2 --- NPB --- p.75 / Chapter 4.3 --- Conclusion --- p.79 / Chapter CHAPTER 5 --- Charge transport properties in double-organic-layer devices with organic-organic heterojunction --- p.81 / Chapter 5.1 --- Introduction --- p.81 / Chapter 5.2 --- Experimental scheme --- p.82 / Chapter 5.3 --- Experimental results and discussion --- p.84 / Chapter 5.3.1 --- ITO/MTDATA/NPB/A1 device --- p.84 / Chapter 5.3.2 --- ITO/MTDATA/Alq3/LiF/Al device --- p.105 / Chapter 5.4 --- Conclusion --- p.115 / Chapter CHAPTER 6 --- Conclusions and future work --- p.101 / Chapter 6.1 --- Conclusions --- p.118 / Chapter 6.2 --- Future work --- p.120 / REFERENCES --- p.122

Notre thèse consiste en l’étude des relations entre la morphologie microscopique et les propriétés optoélectroniques de films minces de matériaux organiques pi-conjugués. En particulier, nous avons porté notre attention sur des oligomères, polymères et copolymères pi-conjugués à base de thiophène et/ou de fluorène, particulièrement intéressants pour des applications dans des dispositifs optiques et électroniques « plastiques ». Nous avons montré que l’assemblage des molécules peut mener à des (nano)structures de taille et de forme spécifiques, par exemple des structures fibrillaires (unidimensionnelles), des plaquettes (bidimensionnelles), ou des agrégats non-texturés, en fonction de l’architecture moléculaire, du solvant et du substrat utilisés dans la préparation des films minces. La modélisation moléculaire nous a permis d’une part de proposer des modèles d’assemblages de molécules au sein des différentes structures, et d’autre part de mieux comprendre l’importance des interactions molécule-molécule et molécule-surface. Nous avons ainsi pu établir les relations entre l’ordre structural au sein de ces dépôts minces et les propriétés optiques et électroniques, en étudiant notamment la photoluminescence à l’état solide ou le transport de charges dans des transistors à effet de champ. Nous avons également eu recours à des techniques de lithographie "douce" pour contrôler l’assemblage des molécules conjuguées, ce qui a permis d’améliorer les performances des dispositifs électroniques. Globalement, les résultats obtenus apportent une meilleure compréhension des relations entre l’organisation des molécules conjuguées à l’état solide et les propriétés optoélectroniques des matériaux conjugués semiconducteurs.

Lighting is a big business, lighting consumes considerable amount of the electricity. These facts motivate for the search of new illumination technologies that are efficient. Semiconductor light emitting diodes (LEDs) have huge potential to replace the traditional primary incandescent lighting sources. They are two basic types of semiconductor LEDs being explored: inorganic and organic semiconductor light emitting diodes. While electroluminescence from p-n junctions was discovered more than a century ago, it is only from the 1960s that their development has accelerated as indicated by an exponential increase of their efficiency and light output, with a doubling occurring about every 36 months, in a similar way to Moore's law in electronics. These advances are generally attributed to the parallel development of semiconductor technologies, optics and material science. Organic light emitting diodes (OLEDs) have rapidly matured during the last 30 years driven by the possibility to create large area light-emitting diodes and displays. Another driving force to specifically use semiconducting polymers is the possibility to build the OLED on conventional flexible substrates via low-cost manufacturing techniques such as printing techniques, which open the way for large area productions. This thesis deals with the demonstration and investigation of heterojunction LEDs based on p-organic semiconductor and n-ZnO nanostructures. The ZnOorganic heterojunctions are fabricated using low cost and simple solution process without the need for sophisticated vacuum equipments. Both ZnO-nanostructures and the organic materials were grown on variety of substrates (i.e. silicon, glass and plastic substrates) using low temperature methods. The growth mechanism of the ZnO nanostructures has been systematically investigated with major focus in ZnO nanorods/nanowires. Different organic semiconductor materials and device configurations are explored starting with single polymer emissive layer ending up with separate emissive and blocking layers, or even blends. Interestingly, the photoluminescence and electroluminescence spectra of the hybrid LEDs provided a broad emission band covering entirely the visible spectrum [∼400-∼800nm]. The hybrid light emitting diode has a white emission attributed to ZnO intrinsic defects and impurities in combination with the electroluminescence from the conjugated polymers. The ZnO nanostructures in contact with a high workfunction electrode constitute an air stable electron injecting contact for the organic semiconductor. Hence, we have shown that a white light emission can be achieved in a ZnO-organic hybrid light emitting diode using cheap and low temperature growth techniques for both organic and inorganic materials. / The series number "1504" is incorrect and is changed in the electronic version to the correct number "1405".