Electrical doping of organic semiconductors with molecular oxidants (p-type) or reductants (n-type) can greatly improve charge injection and conductivity in devices. Simple one electron reductants that are capable of reducing most electron-transport materials will inevitably also be sensitive to reaction with oxygen. Coupling electron transfer step with bond breaking/ making processes in principle can address this problem. The rhodocene dimer and related ruthenium and iridium dimeric sandwich compounds have been discussed as example of such n-dopants, reducing a variety of organic semiconductors to the corresponding radical anions, while forming monomeric cations. This class of n-dopants can be used in both vapor- and solution-processed devices, and the dopant monomer cations are large and, therefore, fairly stable with respect to diffusion. This thesis focused on increasing the utility of these and related electrical dopants. In order to reduce various electron-transport materials with lower electron affinities, which are frequently used in OLEDs, strategies and limitations to develop stronger n-dopants is discussed. Controlling the kinetics of the dopant / semiconductor reactions to allow film processing in ambient conditions, with activation of the dopants being carried out thermally or photochemically in subsequent steps is presented. An approach to covalently tether monomeric cations with themselves, surfaces or electron-transport materials is described. Electrochemical studies that further our understanding of dopant kinetics and thermodynamics is described. The dimer dopant chemistry is also compared to the corresponding hydride-reduced complexes of the cations and manganese tricarbonyl benzene dimer. The directions for future dopant design with improved properties is discussed.

Organic π-conjugated Donor-Acceptor copolymers are emerging as potential candidate materials for organic field effect transistor (OFET) and organic photovoltaic (OPV) applications. The electron-deficient benzothiadiazole group coupled with an electron-rich oligothiophene to form donor-acceptor copolymers has attracted significant attention. These low optical band gap materials absorb photons in the range of 400-800 nm and exhibit good thermal stability. In particular, poly(benzothiadiazole-sexithiophene) (PBT6) exhibits excellent performance in optoelectronic devices and high thermal stability. Here, we present the chemical synthesis and characterization of the polymer, PBT6. Three samples of PBT-6 with differing molecular weights in the range of Mn 18000-45000 Da were synthesized. Each polymer was characterized with respect to its photophysical, thermal properties and field-effected mobility was determined. Devices were prepared by drop-casting polymer solutions in 1,2-dichlorobenzene (DCB) onto an OFET (bottom gate/bottom contact) substrate and the devices were used to examine the charge transport properties of each polymer system. The optimal solvent to be used for processing technique was determined and surface techniques using OTS-8 and OTS-18 were compared through contact angle measurements. The measured charge carrier mobilities were in the range of 0.45-0.6 cm² / V.s. Polymer films prepared via drop-casting and which were thermal annealed exhibit mobilities as high as 0.825 cm² / V.s. This work examines the effect of molecular weight on the charge carrier transport properties and demonstrates the correlation of performance with molecular ordering. Drop-casted films of PBT-6 exhibit highly ordered crystalline lamellar structure with high degree of π- π stacking with edge-on orientation on the substrate. The longer conjugation lengths promote intrachain charge transfer. This high degree of molecular ordering in high MW samples of PBT6 improves the interchain and intrachain charge transfer leading to enhanced mobilities. The increased molecular weight (MW) facilitates in forming more uniform thin films which is vital in processing and application of polymer thin film technologies. These results and observations clearly demonstrate the potential of PBT-6 as a semiconducting material for Optoelectronic devices.

The creation of organic electronics is not only an attractive replacement for amorphous silicon devices, but offers the ability to produce novel technologies such as flexible displays and chemical or biological sensors. Control of the semiconducting film for such devices is of great importance. The fabrication of monolayer devices of a high performance offer a desirable way of creating high sensitivity sensors. Achieving a high level of performance for ultra-thin and monolayer devices, where the charge transport layer is effectively the thickness of the film, requires the careful control of deposition conditions. Thin films of the molecule 5,5'-bis(4-n-hexylphenyl)-2,2'-bithiophene (PTTP) were investigated with respect to their crystal structure, growth dynamics and device performance. Optimised conditions led to the highest reported performance for PTTP, to the best of our knowledge, with mobilities greater than 0.1 cm2V-1s-1. These results allowed the creation of monolayer and multilayer devices, resulting in a saturation thickness of approximately 2.1 monolayers, where the bulk performance was reached. This confirmed the presence of the conduction channel within the first few monolayers and could potentially lead to an optimised device for chemical or biological sensing. The development of a solution processed method for creating monlayers of PTTP was also investigated. Creating a compound with the ability to self assemble on a surface, allowing a controlled monolayer to form, involved the use of a trichlorosilane anchoring group attached to a PTTP core by an alkyl spacer. Solution processed self assembled monolayer field effect transistors (SAMFETs) were formed in less than 10 hours, reaching mobilities as high as 1.7 X 10-2 cm2V-1s-1 . This simple method for creating transistors could further the use of monolayer devices in sensing applications and integrated circuits. Furthermore, the development of solution processed PTTP was undertaken. By blending the small molecule with the insulating polymer PMMA, phase separation of the components led to the creation of thin, crystalline films of PTTP. Working devices were fabricated that required as little as 0.05 \% w/v of the small molecule. This attractive method, of reducing the required material and combination of both insulating and semiconducting components, is a versatile approach to greatly simplify the device processing steps required.

Existem algumas técnicas destinadas ao estudo das características fotofísicas de materiais orgânicos ou dispositivos eletrônicos e optoeletrônicos a base de semicondutores orgânicos. A exemplo disso, a técnica de espectroscopia de absorção fotoinduzida de onda contínua (Continuous Wave Photoinduced Absorption/cw-PIA) apresenta grande sensibilidade como método destinado ao estudo dos processos eletrônicos envolvendo espécies excitadas de vida longa. Esta técnica emprega dois feixes ópticos distintos, um para excitação da amostra e outro (feixe de prova) para investigar os estados excitados remanescentes em amostra após bombeio óptico. O presente trabalho tem como objetivo a construção, desenvolvimento e caracterização de um aparato experimental para espectroscopia cw-PIA. A montagem bem sucedida da técnica foi testada em filme do polímero semicondutor P3HT, em filme de blenda (1:1) de P3HT/PCBM (comumente utilizada como camada ativa em células solares orgânicas) e em filmes automontados camada-a-camada (LbL) do tipo doador-aceitador de carga (P3KHT/P6N), sendo que a molécula P6N foi sintetizada pelo Grupo de Polímeros Bernhard Gross do IFSC-USP. Os filmes LbL de P3KHT/P6N, em comparação aos filmes blenda de P3HT/PCBM, demonstraram uma eficiência maior quanto a geração de portadores de carga com tempo de vida longo. / There are some techniques for the study of photophysical characteristics of organic materials or electronic and optoelectronic devices based on organic semiconductors. For example, the technique of continuous wave photoinduced absorption spectroscopy (cw-PIA) is a highly sensitive method for the study of the electronic processes involving long-lived excited species. This technique uses two distinct optical beams, one for sample excitation and another for probing the excited states remaining in the sample after optical pumping. The present work aims at the construction, development and characterization of an experimental apparatus for cw-PIA spectroscopy. The successful implementation of the technique was tested in a film of the semiconducting polymer P3HT and of the blend (1:1) P3HT/ PCBM (usually employed as active layer in organic solar cells), and also in a Layer-by-Layer (LbL) film of donor-acceptor molecules P3KHT/P6N, where the P6N molecule has been synthesized by Polymer Group Bernhard Gross at IFSC- USP. The comparison between P3KHT / P6N LbL film and the blend P3HT/PCBM has demonstrated higher charge carrier generation efficiency (with long lifetime) for the LbL film.

Organic electronic devices are becoming commonplace in many academic and industrial materials laboratories, and commercial application of these technologies is underway. To maximize our fundamental understanding of organic electronics, a wide array of molecular frameworks is necessary, as it allows for a variety of optical and electronic properties to be systematically investigated. With the ability to further tune each individual scaffold via derivatization, access to a broad spectrum of interesting materials is possible. Of particular interest in the search for organic semiconducting materials are the cyclopenta-fused polyaromatic hydrocarbons, including those based on the fully conjugated indenofluorene (IF) system, which is comprised of five structural isomers. This dissertation represents my recent contributions to this area of research. Chapter I serves as a historical perspective on early indenofluorene research and a review of more current research on their synthesis and applications in organic electronic devices. Chapters II and III cover our early work developing the synthesis of the fully-reduced indeno[1,2-b]fluorene scaffold, with the latter of these chapters showing the first example of its application in an organic electronic device, a field effect transistor. Chapter IV demonstrates the first syntheses of fully-reduced indeno[2,1-c]fluorene derivatives. Chapter V expands our research to encompass isoelectronic heteroatomic derivatives of that same scaffold, introducing the fully-reduced diindeno[2,1-b:1',2'-d]thiophene scaffold and showing that our synthetic methodology also can be used to produce a quinoidal thiophene core. Chapter VI concludes with a review of the similarities between the indeno[2,1-c]fluorene and diindeno[2,1-b:1',2'-d]thiophene molecular architectures and introduces benzo[a]indeno[2,1-b]fluorene derivatives, demonstrating the first example of a fully-reduced indenofluorene that possesses a non-quinoidal core, illustrating that the quinoidal core is not a prerequisite for the strong electron affinities seen across the families of fully-reduced indenofluorenes. This dissertation encompasses previously published and unpublished co-authored material. / 2015-10-10

elementares da eletrônica orgânica, vêm sendo desenvolvidos e integrados para realização de dispositivos eletrônicos de baixo custo, alto volume e flexíveis. Nesta tese foi proposta uma tecnologia para a construção de OFETs sobre substrato flexível e a caracterização destes dispositivos foi feita. Transistores com diferentes comprimentos de canal (L= 5, 10, 20 e 40 μm) foram construídos e avaliados. As características e configuração do poli (álcool vinílico) (PVA) como dielétrico de porta foram definidas através da otimização da reticulação, grau de hidrólise e peso molecular. O PVA utilizado como dielétrico de porta foi de alto peso molecular, hidrolização incompleta e reticulado com dicromato de amônia. O desafio de compatibilização entre os filmes de PVA e poli (3-hexiltiofeno) (P3HT) com diferentes polaridades foi superado e abriu caminho para construção de OFETs e capacitores, estes últimos usados para extrair a capacitância por unidade de área do conjunto PVA-P3HT. Os processos desenvolvidos de fotolitografia e de oxidação por plasma de oxigênio possibilitaram a construção de transistores flexíveis inéditos de Ni-P3HT-PVA-Al com uma arquitetura top-gate, bottom-contacts. Os transistores apresentaram boas características de saída, baixa tensão de operação (< |-6 V|), boa mobilidade (0,015 cm2/V*s) e razões ION/IOFF aceitáveis (~300). A resistência de contato e mobilidade efetiva foram obtidas através do método de linhas de transmissão. Uma boa estabilidade temporal foi atingida, porém ocorreram instabilidades na operação quando os transistores foram testados. A corrente do transistor não se manteve estável, primeiramente aumentou e depois diminuiu com a realização de sucessivas medidas. As razões deste comportamento foram discutidas. Inversores foram demonstrados e caracterizados. O aperfeiçoamento da tecnologia desenvolvida possibilitará a construção de circuitos orgânicos analógicos e digitais para aplicações cotidianas que demandem baixo custo e alto volume. / Organic field effect transistors (OFETs), the elementary components of organic electronics, are constantly developed and integrated to realize low cost, high volume, flexible electronic devices. In this thesis a technology for creating OFETs on flexible substrates is proposed and their characterization is performed. Flexible transistors with different channel lengths (L= 5, 10, 20 and 40 μm) were built and evaluated. The characteristics and configurations of the poly (vinyl alcohol) (PVA) as gate dielectric were defined through the optimization of crosslinking, the degree of hydrolysis and the molecular weight. The chosen PVA is cross-linked with ammonium dichromate, has a high molecular weight and incomplete hydrolization. The challenge of integrating polymers of different polarities: PVA and poly (3-hexyl thiophene) (P3HT), the chosen organic semiconductor, was overcome and opened a path to the construction of OFETs and capacitors. From the later capacitance per unit area was extracted. The developed processes of photolithography and oxygen plasma etching allowed the construction of unprecedented Ni-P3HT-PVA-Al flexible top-gate, bottomcontacts transistors. The transistors showed good output characteristics, low operation voltages (< |-6 V|), acceptable carrier mobilities (0,015 cm2/V*s) and ION/IOFF fractions (~300). Contact resistance and effective mobility were extracted through transmission line method. The transistors showed great temporal stability, but when operated instabilities occurred. The transistor output current first increased and later degraded with successive testing. Organic PMIS inverters were demonstrated and characterized. The optimization of this technology may lead to construction of flexible logic organic devices for everyday applications.

As key components of flexible organic electronics, the synthesis of polythiophenes via less toxic and more cost-effective routes is demanded. An efficient synthetic route for the production of thienyl-containing homopolymers and copolymers has been developed. The synthetic approach consists of: i) the synthesis in high yield and high purity of thienyl borane monomers protected with N-methyliminodiacetic acid (MIDA) via C-H electrophilic borylation. This reaction uses a combination of inexpensive reagents BCl3, AlCl3, and 2,6-dichloropyridine (Cl2Py) for the regioselective electrophilic aromatic substitution of thiophenes, followed by addition of a second aprotic amine pre-esterification to reduce the Brønsted acidity of the reaction mixture. In situ esterification provided the desired thienyl MIDA boronateester monomers in one-pot at room temperature. ii) Subsequent Suzuki-Miyaura polymerisation of the synthesised monomers to produce well defined thienyl containing pie-conjugated polymers in high molecular weight and high yields. Key reaction parameters for successful Suzuki-Miyaura polymerisation of thienyl-derived MIDA boronate esters under mild temperatures (i.e., 55 °C in THF) were found: a) an optimal monomer:H2O:base ratio, which enables controlled hydrolysis of the BMIDA moiety into its corresponding boronic acid at appropriate rates for high fidelity polymerisation. b) Nature of the base, where K3PO4 provided the best results for production of homopolymers (e.g., rr-P3HT), or KOH which gave excellent results for the formation of copolymers across a range of electronically different comonomers (e.g., pCPDT-BT). Thus, it is demonstrated that the approach is a general strategy for the highly efficient production of thienyl containing pie-conjugated regioregular, regiosymmetric and Donor-Acceptor polymers.

This thesis is concerned with study of vibrational dynamics and their effect on charge transport in thin films of organic semiconductors. Two classes of organic semiconductors are investigated- crystalline small molecules and conjugated polymers. Although device performance of both classes of materials has greatly improved over last two decades, detailed understanding of relationship between structure and transport properties is still missing- so far development of organic semiconductors has mostly been based on experimental approach, with theoretical models providing post factum justification rather than guiding rational design of novel compounds. In this thesis I establish methodology to investigate both inter- and intramolecular vibrational modes by combining latest computational techniques with experimental pressure-dependent Raman spectroscopy. The dominant factor limiting charge delocalization in crystalline small molecules are low frequency, large amplitude intermolecular modes. However, theoretical modeling of these modes require use of periodic boundary conditions increasing computational cost by orders of magnitude when compared to commonly used vacuum phase simulations. I report comparative study of two implementations (CRYSTAL09 and CASTEP) of density functional theory (DFT) and dispersion correction (Grimme and Tkatchenko-Scheffler) and evaluate their applicability to predict low frequency vibrational modes in 2,7-Dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT) and 2,8-Difl uoro-5,11-bis(triethylsilylethynyl)anthradithiophene (dif-TES-ADT). Charge transport in conjugated polymers is strongly affected by energetic disorder arising from spatial variations in backbone conformation. I combine vacuum phase DFT simulations of intramolecular vibrational modes with pressure-dependent Raman spectroscopy to study planarity and torsional backbone disorder of 2,5-bis(3-alkylthiophene-2-yl)thieno[3,2-b]thiophene (pBTTT), indacenodithiophene-co-benzo-thiadiazole (IDT-BT), diketopyrrolopyrrole-benzotriazole (DPP-BTZ) and naphtalene-bithiophene (NDI-T2) at pressures up to 3.9 GPa. It is shown that Raman spectra of pBTTT and NDI-T2 demonstrate dependence of mode intensities on hydrostatic pressure, whereas spectra of IDT-BT and DPP-BTZ exhibit lack of dependence. Simulations of theoretical spectra performed as a function of backbone torsion indicate that pBTTT undergoes deplanarization of already non-planar backbone and that NDI-T2 backbone is planarized, whereas backbones of IDT-BT and DPP-BTZ are resilient to changes of conformation. Finally, I perform large scale molecular dynamics simulations of crystalline, semi-crystalline and disordered phases of IDT-BT and DPP-BT in order to investigate effect of disorder on backbone conformation. Both compounds were previously reported to exhibit extremely low degree of energetic disorder- I assign this phenomenon to their surprisingly strong resilience to side chain disorder. In both systems simulations demonstrate novel mechanism of disorder accommodation- their backbones bend rather than twist and retain low degree of torsional variation even in amorphous phase.

Depuis une trentaine d’années, les matériaux organiques semi-conducteurs sont l’objet de recherches fondamentales autant qu’appliquées. Cet intérêt s’explique par des propriétés communément absentes des matériaux inorganiques utilisés jusqu’à présent telles que leur légèreté, leur souplesse et leur mise en forme aisée par des techniques d’impression à bas coût. Cependant, la forte anisotropie de leurs propriétés électroniques, telles que la mobilité des charges, a limité leur intégration dans les appareils de la vie courante.Ainsi, le but de cette thèse est d’étudier de nouveaux concepts de structures moléculaires adaptées au transport de charge tridimensionnel (3D) en phase cristalline. Cette étude concerne la synthèse des molécules, la caractérisation de leurs propriétés optoélectroniques, la résolution de leur structure cristalline, des mesures de dispositifs électroniques ainsi que la modélisation de paramètres clés du transport de charge.Pour atteindre cet objectif, les règles de conception appliquées aux molécules linéaires appartenant à la série du TIPS-pentacene a été étendues à des molécule de symétrie C3h. Les molécules possèdent ainsi un cœur aromatique plan en forme d’étoile à trois bras auxquels sont ajoutés des substituants encombrants proches du centre. Deux empilements sont alors envisagés appelés empilement par les bras ou en colonne décalée pour lesquels un chemin de percolation des sauts de charge est attendu dans les 3 dimensions.Ainsi, 13 triazastarphenes substitués par des amines ou des phényles ont été nouvellement obtenus via des méthodes de synthèses originales et directes. De plus, des systèmes borofluorés ont pu être obtenus ainsi qu’une voie de synthèse originale d’un composé utilisé en OLED. D’autre part, la résolution des structures cristallines a permis d’identifier des empilements proches voir identiques de ceux escomptés. Par exemple, deux benzostarphenes présentent respectivement un empilement par les bras sur la moitié de la maille et un empilement en colonne décalée. Enfin, l’étude théorique a mis en évidence que le transport de charge devrait s’effectuer en 2D pour le premier cas et en 3D pour le second en phase cristalline.Finalement, ce travail décrit pour la première fois la synthèse de composés étendus et solubles en forme d’étoile basés sur un motif acridine. Au-delà des multiples études sur les propriétés de ces molécules ainsi que de leurs intégrations quelquefois réussies dans des dispositifs électroniques (OFETs ou cellules à solaires à perovskites), les nouvelles méthodes de synthèse et les empilements discutés en détails devraient contribuer à l’élaboration de nouvelles règles de conception de composé -conjugué et participer au développement de semi-conducteurs organiques de plus hautes performances. / The research in organic electronics has attracted worldwide attention due to the specific properties of organic materials such as lightness, flexibility, large scale processing ability and low production cost. Compared with inorganic materials, the strong anisotropy and low charge carrier transport mobility limit their integrations in commercial devices. This research aims at developing molecule systems leading to three-dimensional charge transport.To reach this goal, our design strategy is to expand the generally linear-shaped molecular structure into star-shaped structure with C3h symmetry. The designed molecules consist of a planar core of fused aromatic cycles to form efficient - stacking with neighboring molecules and of bulky groups located close to the center to increase the solubility of the materials and prevent 1D columnar packing. Thus, two supramolecular arrangements are speculated (arm and column packing) where charge hopping follows pathways in 3D.Based on this design, 13 triazastarphenes substituted directly by amine or phenyl groups were synthesized and thoroughly characterized. Their electronic properties were carefully determined by UV-visible absorption spectroscopy, cyclic voltammetry and DFT calculations. Results from single crystal XRD showed that the experimental packing is similar to model for few molecules. In detail, one amino-triazastarphene has shown a new 2D layer by layer packing motif, while benzo-triazastarphenes have led to column packing in one case and half arm packing for another as expected. In addition, theoretical approach highlighted 2D and 3D dimensionality for charge carrier transport for the two later examples in the crystal phase.Finally, this work is the first report about straightforward synthesis of extended C3h acridine derivatives. Even though the performances obtained from the devices (OFETs and perovskite solar cells) based on these materials did not reach state of the art performances, the novel synthetic method and the achievement of interesting molecular arrangement motifs in single crystal can contribute to the development of high-performance OSCs.

<p>Electrochemical Transistor(ECT) was reported by David Nilsson in 2002. Later,its dimensios were specified and a SPICE model was developed.</p><p>The main purpose of this diploma work is to check the performance of electrochemical transistors in amplifier circuits. Simple amplifier circuits were simulated using SPICE model of ECT. Lateral and Vertical structures of electrochemical transistors were patterned on orgacon sheet(provided by AGFA),with various electrolytes(EG010,MS-HEC & MS-L). Characteric curves and time responses of these transistors were studied and then were then used as an active component in single amplifier circuits. Screen printed ECT's were also checked with the best available electrolyte. Behaviour of self made and screen printed ECT's were compared on the basis of on-off ratio,slew rate,frequency response and gain. Screen printed transistors showed promising results having less deterioration with time  but  till  an  an  input  signal  frequency  of  2Hz  only. Mismatch with simulation results and Shockley's equation were other findings after data analysis.</p><p><img src="file:///C:/DOCUME%7E1/zia/LOCALS%7E1/Temp/moz-screenshot.jpg" /><img src="file:///C:/DOCUME%7E1/zia/LOCALS%7E1/Temp/moz-screenshot-1.jpg" /></p>