An electrical driven organic solid state laser is a very challenging goal which is so far well beyond reach. As a step towards realization, we monolithically implemented an Organic Light Emitting Diode (OLED) into a dielectric, high quality microcavity (MC) consisting of two Distributed Bragg Reflectors (DBR). In order to account for an optimal optical operation, the OLED structure has to be adapted. Furthermore, we aim to excite the device not only electrically but optically as well. Different OLED structures with an emission layer consisting of Alq3:DCM (2 wt%) were investigated. The External Quantum Efficiencies (EQE) of this hybrid structures are in the range of 1-2 %, as expected for this material combination. Including metal layers into a MC is complicated and has a huge impact on the device performance. Using Transfer-Matrix-Algorithm (TMA) simulations, the best positions for the metal electrodes are determined. First, the electroluminescence (EL) of the adjusted OLED structure on top of a DBR is measured under nitrogen atmosphere. The modes showed quality factors of Q = 60. After the deposition of the top DBR, the EL is measured again and the quality factors increased up to Q = 600. Considering the two 25-nm-thick-silver contacts a Q-factor of 600 is very high. The realization of a suitable encapsulation method is important. Two approaches were successfully tested. The first method is based on the substitution of a DBR layer with a layer produced via Atomic Layer Deposition (ALD). The second method uses a 0.15-mm-thick cover glass glued on top of the DBR with a 0.23-µm-thick single-component glue layer. Due to the working encapsulation, it is possible to investigate the sample under ambient conditions.

In the scope of this diploma thesis the optical properties of organic multilayers and mixed layers were investigated by means of spectroscopic ellipsometry und infrared spectroscopy. The samples were prepared by organic molecular beam deposition in high vacuum on hydrogen passivated Silicon(111) substrates. The structures consist either of N,N-Di(naphthalene-1-yl)-N,N`-diphenyl-benzidine (a-NPD) and tris(8-hydroxyquinoline) aluminium (Alq3) or 3,4,9,10-perylene-tetracarboxylic dianhydride (PTCDA) and copper phthalocyanine (CuPc). The optical response of the multilayers consisting of Alq3 and a-NPD could be modelled using the isotropic dielectric functions of single layers assuming sharp interfaces. The planar structure of PTCDA and the CuPc molecules and their orientation in the stack lead to an overlapping of the p-orbitals strongly influencing the optical properties and the orientation of the molecules. It was found that in multilayers as well as in mixed layers the CuPc molecules adopt the orientation of PTCDA molecules with the molecular plane parallel to the substrate. The multilayers were described using the anisotropic dielectric functions of the constituents including intermixing and roughness at the interfaces. The deviation between the simulation and the experiment suggests an electronic interaction due to coupling between the p-orbitals of CuPc and PTCDA at the interfaces. The simulation of the mixed layers reveals a change in line shape of the Q-band of CuPc. Beside ellipsometry and infrared spectroscopy techniques like x-ray reflectometry and AFM were used for investigations. Additionally in this diploma thesis a special sample holder and manipulator was designed with which in-situ-ellipsometry measurements in ultra high vacuum can be performed. / Im Rahmen dieser Diplomarbeit wurden die optischen Eigenschaften von organischen Multilayern und Mischschichten untersucht. Die Schichtstrukturen wurden im Hochvakuum nach dem Verfahren der organischen Molekularstrahldeposition (OMBD) auf H-passivierten Silizium(111)-Substraten hergestellt. Die optische Charakterisierung erfolgte mit dem Verfahren der spektroskopischen Ellipsometrie und der Infrarotspektroskopie. Dabei wurden zwei verschiedene Materialienpaarungen untersucht, die zum einen aus den organischen Substanzen Aluminium 8-Hydroxichinolat (Alq3) und N,N'-Di(1-naphthyl)-N,N'-diphenylbenzidin (a-NPD) und zum anderen aus Perylentetracarbonsäuredianhydrid (PTCDA) und Kupferphthalocyanin (CuPc) bestanden. Das optische Verhalten der Multilayer und der Mischschichten bestehend aus Alq3 und a-NPD konnte mit den isotropen dielektrischen Funktionen der Einzelschichten simuliert werden. In den PTCDA/CuPc-Schichtsystemen führt die planare Struktur der Moleküle zu einer starken Überlappung der p-Orbitale, was einen großen Einfluss auf die optischen Eigenschaften und die Orientierung der Moleküle hat. Es wurde festgestellt, dass sowohl in den Multilayern als auch in den Mischschichten die CuPc-Moleküle die Anordnung der PTCDA-Moleküle annehmen. Die Multilayer wurden unter Verwendung der anisotropen dielektrischen Funktionen der beteiligten Materialien und unter Berücksichtigung von Grenzflächenrauhigkeit simuliert. Die Unterschiede zwischen Experiment und Modell sind auf eine Kopplung zwischen den p-Orbitalen zurückzuführen. Die Simulationen der Mischschichten zeigten eine Veränderung der Linienform des Q-Bandes von CuPc. Als Untersuchungsmethoden kamen neben der Ellipsometrie und der Infrarotspektroskopie auch die Röntgen-Reflektometrie und das AFM zum Einsatz. Darüber hinaus wurde in dieser Arbeit eine Messeinrichtung aufgebaut, mit der in-situ-Ellipsometriecharakterisierung von Proben im Ultrahochvakuum möglich ist.

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Organic semiconductors (OSCs) present an electron mobility lower by several orders of magnitude than the hole mobility, giving rise to an electron-hole charge imbalance in organic devices such as organic light-emitting diodes (OLEDs) and organic light-emitting transistors (OLETs). In this thesis project, I tried to achieve an efficient electron transport and injection properties in opto-electronic devices, using inorganic n-type metal oxides (MOs) instead of organic n-type materials and a polyethyleneimine ethoxylated (PEIE) thin layer as electron transport (ETLs) and injection layers (EILs), respectively. In the first part of this thesis, inverted OLEDs were fabricated in order to study the effect of the PEIE layer in-between ZnO and two different emissive layers (EMLs): poly(9,9-dioctylfluorene-alt-benzothiadiazole) polymer (F8BT) and tris(8-hydroxyquinolinato) aluminum small molecule (Alq3), based on a solution and thermal evaporation processes, respectively. Different concentrations (0.80 %, 0.40 %) of PEIE layers were used to further study electron injection capability in OLEDs. After a series of optimizations in the fabrication process, the opto-electrical characterization showed high-performance of devices. The inverted OLEDs reported a maximum luminance over 104 cd m-2 and a maximum external quantum efficiency (EQE) around 1.11 %. The results were attributed to the additional PEIE layer which provided a good electron injection from MOs into EMLs. In the last part of the thesis, OLETs were fabricated and discussed by directly transferring the energy modification layer from OLEDs to OLETs. As metal oxide layer, ZnO:N was employed for OLETs since ZnO:N-based thin film transistors (TFTs) showed better performance than ZnO-based TFTs. Finally, due to their short life-time, OLETs were characterized electrically but not optically.

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Submitted by OSWALDO NUNES NETO null (netfisic@fc.unesp.br) on 2016-08-13T20:37:55Z No. of bitstreams: 1 Tese_Doutorado_Oswaldo.pdf: 4276326 bytes, checksum: e73a2086ffde0d12d2f5875fb168f8c1 (MD5) / Approved for entry into archive by Ana Paula Grisoto (grisotoana@reitoria.unesp.br) on 2016-08-16T14:27:21Z (GMT) No. of bitstreams: 1 nunesneto_o_dr_bauru.pdf: 4276326 bytes, checksum: e73a2086ffde0d12d2f5875fb168f8c1 (MD5) / Made available in DSpace on 2016-08-16T14:27:21Z (GMT). No. of bitstreams: 1 nunesneto_o_dr_bauru.pdf: 4276326 bytes, checksum: e73a2086ffde0d12d2f5875fb168f8c1 (MD5) Previous issue date: 2016-04-28 / Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / Materiais e dispositivos baseados em compostos orgânicos desempenham um importante papel em diversas áreas da aplicação tecnológica devido às suas interessantes propriedades eletro-magneto- ópticas, adicionadas às suas características mecânicas únicas, facilidade de processamento, versatilidade de síntese e baixo custo relativo. Apesar do proeminente campo de aplicação destes materiais, muitos aspectos associados à sua ciência básica são ainda pouco compreendidos. Nesse cenário destaca-se o fenômeno de Magnetoresistência Orgânica (OMAR, da sigla em inglês). Tal fenômeno encontra-se associado a variações significativas da condutividade elétrica de dispositivos orgânicos induzidas por pequenos campos magnéticos externos em temperatura ambiente e tem sido observado em diversificados materiais poliméricos e moleculares. No presente trabalho avaliou-se o fenômeno de OMAR apresentado por um Diodo Emissor de Luz baseado na molécula de Alq3. Medidas de Espectroscopia de Impedância Elétrica na presença de um Campo Magnético estático externo (EIE-CM) foram realizadas sobre o referido dispositivo para diferentes temperaturas. Métodos diferenciados de aquisição e manipulação de dados foram empregados a fim de remover a dependência temporal dos sinais tipicamente observados. Os seguintes Efeitos de Campo Magnético (MFE, da sigla em inglês) foram observados sobre a resposta elétrica do dispositivo: (i) redução de cerca de 1% na resistência, efeito praticamente constante para todo o espectro de frequência e; (ii) variações significativas na capacitância, com intensificação do efeito de Capacitância Negativa em baixas frequências. Como suporte para a interpretação dos resultados experimentais foram realizadas simulações empregando-se duas abordagens: Circuitos Equivalentes e Análise de perturbações de pequenos sinais (em inglês, Small Signal Analysis ) via soluções numéricas das equações de transporte de Boltzmann numa aproximação por Drift-Diffusion empregando-se dispositivos simplificados. As análises sugerem que os MFE evidenciados podem estar associados a um aumento da mobilidade efetiva dos portadores de carga e a uma redução na taxa de recombinação bimolecular no dispositivo. Os resultados foram interpretados em termos dos modelos atualmente aceitos para o fenômeno de OMAR. Esta tese também apresenta um estudo de processos de geração e transferência de carga em corantes Cianinas, materiais promissores para aplicações em células solares com absorção no infravermelho. Técnicas de Ressonância de Spin Eletrônico induzida por Luz foram empregadas em blendas destes corantes com o polímero MEH-PPV e com o fulereno (C60) a fim de avaliar, respectivamente, o caráter aceitador e doador de elétrons das Cianinas. / Materials and devices based on organic compounds play an important role in various technological applications, mainly due to their interesting electrical-magneto-optical properties combined with their unique mechanical properties, easy processing, versatility of synthesis and relatively low cost. Despite the prominent application field of these materials many aspects associated with their basic science are still not well understood. In this context the Organic Magnetoresistance phenomenon (OMAR) deserves to be highlighted. This phenomenon is associated with significant changes in the electrical conductivity of organic devices induced by the presence of small external magnetic fields at room temperature, being observed in various polymeric and molecular materials. In this study we have investigated the OMAR phenomenon in Alq3-based OLEDs. Electrical impedance spectroscopy technique in the presence of an external static magnetic field (EIS-MF) was employed in the experiments; distinct temperatures were considered. Differentiated methods of acquisition and data manipulation were employed to remove the typically observed signal time dependence. The following magnetic field effects (MFE) were observed on the electrical response of the device: (i) a constant reduction of around 1% in the resistance over the entire frequency spectrum and; (ii) significant changes in the capacitance followed by an intensification of the negative capacitance effect at low frequencies. Simulations employing two different approaches were carried out for the interpretation of the experimental results: (i) Equivalent Circuits and (ii) Small Signal Analysis via numerical solutions of the Boltzmann transport equations by Drift-Diffusion approach. The results suggest that the observed MFE can be associated with an increase in the effective mobility of the charge carriers and a reduction in the bimolecular recombination rate in the device. The results were interpreted in terms of the currently accepted models for the OMAR phenomenon. This thesis also presents a study about generation and charge transfer processes in cyanine dyes (near infrared absorbing compounds) which are promising materials for applications in solar cells. Light induced Electron Spin Resonance (L-ESR) technique was employed to study the presence/formation of paramagnetic centers in blends of these dyes with MEH-PPV polymer and fullerene (C60) to evaluate, respectively, the electron acceptor and donor character of cyanine dyes. / FAPESP: 2011/21830-6 / CNPq: 204432/2013-8