Neste trabalho, foram investigados os processos de migração e dissociação do éxciton em filmes ultrafinos de poli(9,9 dioctilfluoreno) (PFO) com espessura menores que o raio típico de migração excitônica (10 nm) próximos de interface semicondutora orgânica e inorgânica. Os filmes de PFO foram produzidos utilizando a técnica de <span style=\'color:black;font-style:italic;language:PT-BR\'>spin-coating<span style=\'color:black;language:PT-BR\'> a partir de soluções de PFO em clorofórmio e em tolueno. Sabe-se que ao se utilizar o clorofórmio como solvente, os filmes de PFO apresentam uma estrutura amorfa. Com isso foi possível obter filmes com espessuras menores que o raio de migração do éxciton com qualidades ideais para o estudo de processos fotofísicos. Esses filmes foram depositados sobre uma camada de nanopartículas de dióxido de titânio (TiO<span style=\'color:black;language:PT-BR\'>2<span style=\'color:black;language:PT-BR\'>) formando assim uma interface orgânica/inorgânica. Técnicas espectroscópicas, tais como, microscopia confocal de fluorescência (LSCM), microscopia de imagem do tempo de vida (FLIM), fotoluminescência de onda contínua e resolvida no tempo bem como espectroscopia de absorção foram utilizadas no presente trabalho. Inicialmente o espectro de fotoluminescência dos filmes de PFO foram caracterizados através da dependência da intensidade da transição puramente eletrônica <span style=\'color:black;font-style:italic;language:PT-BR\'>I<span style=\'color:black;language:PT-BR\'>, largura da linha a meia altura <span style=\'font-family:Symbol;color:black;language:PT-BR\'>G<span style=\'color:black;language:PT-BR\'>o<span style=\'color:black; language:PT-BR\'>, energia da transição puramente eletrônica <span style=\'color:black;font-style:italic;language:PT-BR\'>E<span style=\'color:black;language:PT-BR\'> e parâmetro de Huang-Rhys <span style=\'color:black;font-style:italic;language:PT-BR\'>S<span style=\'color:black;language:PT-BR\'> variando a temperatura. Verificou-se que a intensidade pode ser descrita em termos da ativação térmica da migração do éxciton. Além disso, a temperatura introduz uma desordem térmica que afeta diretamente o tamanho dos segmentos conjugados que é observado em termos dos parâmetros, <span style=\'font-family:Symbol;color:black;language:PT-BR\'>G<span style=\'color:black;language:PT-BR\'>o<span style=\'color:black; language:PT-BR\'>, <span style=\'color:black;font-style:italic; language:PT-BR\'>E<span style=\'color:black;language:PT-BR\'> e <span style=\'color:black;font-style:italic;language:PT-BR\'>S<span style=\'color:black;language:PT-BR\'>. Com os filmes de PFO produzidos com o solvente tolueno foi observado que frações de fase <span style=\'font-family:\"Times New Roman\";color:black;font-style:italic; language:EL\'>&#946;<span style=\'font-family:\"Times New Roman\"; color:black;language:EL\'> <span style=\'color:black;language:PT-BR\'>já são induzidas nesses filmes e que esta fase não está dispersa na matriz amorfa e sim em forma de domínios formados por moléculas na fase <span style=\'font-family:\"Times New Roman\";color:black;font-style:italic; language:EL\'>&#946; <span style=\'color:black;language:PT-BR\'>que correspondente ao ordenamento nos anéis aromáticos do PFO. Também foi observado que nos filmes com espessura menor que 10 nm preparados em clorofórmio, a fase <span style=\'font-family:\"Times New Roman\";color:black;font-style:italic; language:EL\'>&#946;<span style=\'font-family:\"Times New Roman\"; color:black;language:EL\'> <span style=\'color:black;language:PT-BR\'>é induzida e sugerimos que isso ocorre devido a forte interação filme/substrato. Além disso, outros métodos bem conhecidos na literatura, tais como, tratamento a vapor de tolueno e ciclos térmicos de resfriamento/aquecimento foram utilizados para induzir a fase <span style=\'font-family:\"Times New Roman\";color:black;font-style:italic; language:EL\'>&#946;<span style=\'font-family:\"Times New Roman\"; color:black;language:EL\'> <span style=\'color:black;language:PT-BR\'>em filmes de PFO amorfo. Com relação aos filmes contendo a interface TiO<span style=\'color:black;language:PT-BR\'>2<span style=\'color:black;language:PT-BR\'>/PFO, a dissociação do éxciton na interface foi observada através da redução da intensidade da fotoluminescência. Em filmes ultrafinos, a eficiência do processo de dissociação do éxciton na interface é superior a 90%. A partir desses resultados, obteve-se que o raio de migração do éxciton no PFO é de (13 <span style=\'font-family:Symbol;color:black;language:PT-BR\'>±<span style=\'color:black;language:PT-BR\'> 3) nm. Além disso, devido à alta fluência (~ 10<span style=\'color:black;language:PT-BR\'>25<span style=\'color:black;language:PT-BR\'> fótons/cm<span style=\'color:black;language:PT-BR\'>2<span style=\'color:black;language:PT-BR\'>s), efeitos de autoaniquilamento de éxcitons em filmes ultrafinos foram observados nas medidas de tempo de decaimento radiativo. Por fim, em filmes de PFO (contendo a fase <span style=\'font-family:\"Times New Roman\";color:black;font-style:italic; language:EL\'>&#946;<span style=\'font-family:\"Times New Roman\"; color:black;language:EL\'>) <span style=\'color:black;language:PT-BR\'>depositados sobre o TiO<span style=\'color:black;language:PT-BR\'>2<span style=\'color:black;language:PT-BR\'>, somente os éxcitons das regiões amorfas migram até a interface do TiO<span style=\'color:black;language:PT-BR\'>2<span style=\'color:black;language:PT-BR\'> e são dissociados por ela. A energia térmica a temperatura ambiente promove uma maior eficiência da dissociação do éxciton do que em baixas temperaturas (~5 K). No entanto, mesmo em temperatura ambiente, as moléculas de fase <span style=\'font-family:\"Times New Roman\";color:black;font-style:italic; language:EL\'>&#946;<span style=\'font-family:\"Times New Roman\"; color:black;language:EL\'> <span style=\'color:black;language:PT-BR\'>atuam como centros de captura dos éxcitons competindo com o processo de dissociação. A partir desses resultados, obteve-se que o raio de transferência de energia no PFO é igual a (3,5 <span style=\'color:black;text-decoration:underline;language:PT-BR\'>+<span style=\'color:black;language:PT-BR\'> 0,5) nm.<span style=\'color:black; language:PT-BR\'> <![if !vml]> <![endif]> / In this work, we investigated the process of exciton dissociation and migration in ultra-thin films of poly (9,9 dioctilfluoreno) (PFO) with a thickness smaller than the typical radius of excitonic migration (10 nm) and near to organic and inorganic semiconductor interface. The PFO films were produced using the spin-coating technique from a PFO solution in chloroform and toluene. It is known that when using chloroform as solvent, the PFO films have an amorphous structure. Thus, it was possible to obtain films that have thicknesses smaller than the radius of the exciton migration qualities, which is ideal to study photophysical processes. These films were deposited on the titanium dioxide (TiO<span style=\'language:EN\'>2<span style=\'language:EN\'>) nanoparticles layer forming an organic/inorganic interface. Spectroscopic techniques such as fluorescence confocal microscopy (LSCM), fluorescence lifetime imaging microscopy (FLIM), continuous wave photoluminescence and time resolved and absorption spectroscopy were used in this study. First, the photoluminescence spectrum of PFO films were characterized by the dependence of the purely electronic transition intensity <span style=\'font-style:italic;language:EN\'>I<span style=\'language:EN\'>, full width at half maximum <span style=\'font-family:Symbol;language:EN\'>G<span style=\'language: EN\'>o<span style=\'language:EN\'>, purely electronic transition energy <span style=\'font-style:italic;language:EN\'>E<span style=\'language:EN\'> and Huang-Rhys parameter <span style=\'font-style:italic;language:EN\'>S <span style=\'language:EN\'>with the temperature. It was showed that the intensity can be described according to thermal activation of the exciton migration. Furthermore, the temperature introduces a thermal disorder affecting directly the conjugated segment length which is observed according to the parameters, <span style=\'font-family:Symbol;language:EN\'>G<span style=\'language: EN\'>o<span style=\'language:EN\'>, <span style=\'font-style: italic;language:EN\'>E<span style=\'language:EN\'> e <span style=\'font-style:italic;language:EN\'>S<span style=\'language:EN\'>. The PFO films produced with the solvent toluene analysis showed that the fractions of <span style=\'font-family:\"Times New Roman\";font-style:italic;language:EN\'>&#946;<span style=\'language:EN\'> phase are already induced and that this phase is not dispersed in the amorphous matrix. On the order hand, they are shaped domains formed by <span style=\'font-family:\"Times New Roman\";font-style:italic;language:EN\'>&#946;<span style=\'language:EN\'> phase molecules that are related to the PFO aromatic rings organization. It was also observed that the films with thickness smaller than 10 nm prepared using chloroform, the <span style=\'font-family:\"Times New Roman\";font-style:italic;language:EN\'>&#946;<span style=\'language:EN\'> phase is induced, which may be occurring due to the strong interaction observed between film and substrate. Other methods reported in the literature, such as toluene steam treatment and thermal cycles of cooling/heating were used to induce <span style=\'font-family:\"Times New Roman\";font-style:italic;language:EN\'>&#946;<span style=\'language:EN\'> phase in amorphous PFO films as well. The exciton dissociation at the interface in films containing TiO<span style=\'language:EN\'>2<span style=\'language:EN\'>/PFO interface were observed by reduction of photoluminescence intensity; and this same efficiency in ultra-thin films is higher than 90%. From these results, it was reported that the exciton migration radius in PFO is (13 <span style=\'font-family:Symbol;language:EN\'>±<span style=\'language:EN\'> 3) nm. Furthermore, effects of excitons annihilation in ultra-thin films were observed in the decay time radiative measurements due to high fluency (~ 10<span style=\'language:EN\'>25<span style=\'language:EN\'> photons/cm<span style=\'language:EN\'>2<span style=\'language:EN\'>s). Finally, in PFO films (with the <span style=\'font-family:\"Times New Roman\";font-style:italic;language:EN\'>&#946;<span style=\'language:EN\'> phase) deposited on the TiO<span style=\'language:EN\'>2 <span style=\'language:EN\'>just the exciton of amorphous regions migrates to the TiO<span style=\'language:EN\'>2<span style=\'language:EN\'> interface, which dissociates them. The thermal energy at room temperature promotes higher efficiency than the exciton dissociation at low temperatures (~ 5 K). However, even at room temperature, the <span style=\'font-family:\"Times New Roman\";font-style:italic;language:EN\'>&#946;<span style=\'language:EN\'> phase molecules act as the most important molecules to capture exciton, competing to the exciton dissociation process. These results conducted to conclude that the energy transfer radius in PFO is equal to (3.5 <span style=\'text-decoration:underline;language:EN\'>+<span style=\'language: EN\'> 0.5) nm. <![if !vml]> <![endif]>

Neste trabalho, foram investigados os processos de migração e dissociação do éxciton em filmes ultrafinos de poli(9,9 dioctilfluoreno) (PFO) com espessura menores que o raio típico de migração excitônica (10 nm) próximos de interface semicondutora orgânica e inorgânica. Os filmes de PFO foram produzidos utilizando a técnica de <span style=\'color:black;font-style:italic;language:PT-BR\'>spin-coating<span style=\'color:black;language:PT-BR\'> a partir de soluções de PFO em clorofórmio e em tolueno. Sabe-se que ao se utilizar o clorofórmio como solvente, os filmes de PFO apresentam uma estrutura amorfa. Com isso foi possível obter filmes com espessuras menores que o raio de migração do éxciton com qualidades ideais para o estudo de processos fotofísicos. Esses filmes foram depositados sobre uma camada de nanopartículas de dióxido de titânio (TiO<span style=\'color:black;language:PT-BR\'>2<span style=\'color:black;language:PT-BR\'>) formando assim uma interface orgânica/inorgânica. Técnicas espectroscópicas, tais como, microscopia confocal de fluorescência (LSCM), microscopia de imagem do tempo de vida (FLIM), fotoluminescência de onda contínua e resolvida no tempo bem como espectroscopia de absorção foram utilizadas no presente trabalho. Inicialmente o espectro de fotoluminescência dos filmes de PFO foram caracterizados através da dependência da intensidade da transição puramente eletrônica <span style=\'color:black;font-style:italic;language:PT-BR\'>I<span style=\'color:black;language:PT-BR\'>, largura da linha a meia altura <span style=\'font-family:Symbol;color:black;language:PT-BR\'>G<span style=\'color:black;language:PT-BR\'>o<span style=\'color:black; language:PT-BR\'>, energia da transição puramente eletrônica <span style=\'color:black;font-style:italic;language:PT-BR\'>E<span style=\'color:black;language:PT-BR\'> e parâmetro de Huang-Rhys <span style=\'color:black;font-style:italic;language:PT-BR\'>S<span style=\'color:black;language:PT-BR\'> variando a temperatura. Verificou-se que a intensidade pode ser descrita em termos da ativação térmica da migração do éxciton. Além disso, a temperatura introduz uma desordem térmica que afeta diretamente o tamanho dos segmentos conjugados que é observado em termos dos parâmetros, <span style=\'font-family:Symbol;color:black;language:PT-BR\'>G<span style=\'color:black;language:PT-BR\'>o<span style=\'color:black; language:PT-BR\'>, <span style=\'color:black;font-style:italic; language:PT-BR\'>E<span style=\'color:black;language:PT-BR\'> e <span style=\'color:black;font-style:italic;language:PT-BR\'>S<span style=\'color:black;language:PT-BR\'>. Com os filmes de PFO produzidos com o solvente tolueno foi observado que frações de fase <span style=\'font-family:\"Times New Roman\";color:black;font-style:italic; language:EL\'>&#946;<span style=\'font-family:\"Times New Roman\"; color:black;language:EL\'> <span style=\'color:black;language:PT-BR\'>já são induzidas nesses filmes e que esta fase não está dispersa na matriz amorfa e sim em forma de domínios formados por moléculas na fase <span style=\'font-family:\"Times New Roman\";color:black;font-style:italic; language:EL\'>&#946; <span style=\'color:black;language:PT-BR\'>que correspondente ao ordenamento nos anéis aromáticos do PFO. Também foi observado que nos filmes com espessura menor que 10 nm preparados em clorofórmio, a fase <span style=\'font-family:\"Times New Roman\";color:black;font-style:italic; language:EL\'>&#946;<span style=\'font-family:\"Times New Roman\"; color:black;language:EL\'> <span style=\'color:black;language:PT-BR\'>é induzida e sugerimos que isso ocorre devido a forte interação filme/substrato. Além disso, outros métodos bem conhecidos na literatura, tais como, tratamento a vapor de tolueno e ciclos térmicos de resfriamento/aquecimento foram utilizados para induzir a fase <span style=\'font-family:\"Times New Roman\";color:black;font-style:italic; language:EL\'>&#946;<span style=\'font-family:\"Times New Roman\"; color:black;language:EL\'> <span style=\'color:black;language:PT-BR\'>em filmes de PFO amorfo. Com relação aos filmes contendo a interface TiO<span style=\'color:black;language:PT-BR\'>2<span style=\'color:black;language:PT-BR\'>/PFO, a dissociação do éxciton na interface foi observada através da redução da intensidade da fotoluminescência. Em filmes ultrafinos, a eficiência do processo de dissociação do éxciton na interface é superior a 90%. A partir desses resultados, obteve-se que o raio de migração do éxciton no PFO é de (13 <span style=\'font-family:Symbol;color:black;language:PT-BR\'>±<span style=\'color:black;language:PT-BR\'> 3) nm. Além disso, devido à alta fluência (~ 10<span style=\'color:black;language:PT-BR\'>25<span style=\'color:black;language:PT-BR\'> fótons/cm<span style=\'color:black;language:PT-BR\'>2<span style=\'color:black;language:PT-BR\'>s), efeitos de autoaniquilamento de éxcitons em filmes ultrafinos foram observados nas medidas de tempo de decaimento radiativo. Por fim, em filmes de PFO (contendo a fase <span style=\'font-family:\"Times New Roman\";color:black;font-style:italic; language:EL\'>&#946;<span style=\'font-family:\"Times New Roman\"; color:black;language:EL\'>) <span style=\'color:black;language:PT-BR\'>depositados sobre o TiO<span style=\'color:black;language:PT-BR\'>2<span style=\'color:black;language:PT-BR\'>, somente os éxcitons das regiões amorfas migram até a interface do TiO<span style=\'color:black;language:PT-BR\'>2<span style=\'color:black;language:PT-BR\'> e são dissociados por ela. A energia térmica a temperatura ambiente promove uma maior eficiência da dissociação do éxciton do que em baixas temperaturas (~5 K). No entanto, mesmo em temperatura ambiente, as moléculas de fase <span style=\'font-family:\"Times New Roman\";color:black;font-style:italic; language:EL\'>&#946;<span style=\'font-family:\"Times New Roman\"; color:black;language:EL\'> <span style=\'color:black;language:PT-BR\'>atuam como centros de captura dos éxcitons competindo com o processo de dissociação. A partir desses resultados, obteve-se que o raio de transferência de energia no PFO é igual a (3,5 <span style=\'color:black;text-decoration:underline;language:PT-BR\'>+<span style=\'color:black;language:PT-BR\'> 0,5) nm.<span style=\'color:black; language:PT-BR\'> <![if !vml]> <![endif]> / In this work, we investigated the process of exciton dissociation and migration in ultra-thin films of poly (9,9 dioctilfluoreno) (PFO) with a thickness smaller than the typical radius of excitonic migration (10 nm) and near to organic and inorganic semiconductor interface. The PFO films were produced using the spin-coating technique from a PFO solution in chloroform and toluene. It is known that when using chloroform as solvent, the PFO films have an amorphous structure. Thus, it was possible to obtain films that have thicknesses smaller than the radius of the exciton migration qualities, which is ideal to study photophysical processes. These films were deposited on the titanium dioxide (TiO<span style=\'language:EN\'>2<span style=\'language:EN\'>) nanoparticles layer forming an organic/inorganic interface. Spectroscopic techniques such as fluorescence confocal microscopy (LSCM), fluorescence lifetime imaging microscopy (FLIM), continuous wave photoluminescence and time resolved and absorption spectroscopy were used in this study. First, the photoluminescence spectrum of PFO films were characterized by the dependence of the purely electronic transition intensity <span style=\'font-style:italic;language:EN\'>I<span style=\'language:EN\'>, full width at half maximum <span style=\'font-family:Symbol;language:EN\'>G<span style=\'language: EN\'>o<span style=\'language:EN\'>, purely electronic transition energy <span style=\'font-style:italic;language:EN\'>E<span style=\'language:EN\'> and Huang-Rhys parameter <span style=\'font-style:italic;language:EN\'>S <span style=\'language:EN\'>with the temperature. It was showed that the intensity can be described according to thermal activation of the exciton migration. Furthermore, the temperature introduces a thermal disorder affecting directly the conjugated segment length which is observed according to the parameters, <span style=\'font-family:Symbol;language:EN\'>G<span style=\'language: EN\'>o<span style=\'language:EN\'>, <span style=\'font-style: italic;language:EN\'>E<span style=\'language:EN\'> e <span style=\'font-style:italic;language:EN\'>S<span style=\'language:EN\'>. The PFO films produced with the solvent toluene analysis showed that the fractions of <span style=\'font-family:\"Times New Roman\";font-style:italic;language:EN\'>&#946;<span style=\'language:EN\'> phase are already induced and that this phase is not dispersed in the amorphous matrix. On the order hand, they are shaped domains formed by <span style=\'font-family:\"Times New Roman\";font-style:italic;language:EN\'>&#946;<span style=\'language:EN\'> phase molecules that are related to the PFO aromatic rings organization. It was also observed that the films with thickness smaller than 10 nm prepared using chloroform, the <span style=\'font-family:\"Times New Roman\";font-style:italic;language:EN\'>&#946;<span style=\'language:EN\'> phase is induced, which may be occurring due to the strong interaction observed between film and substrate. Other methods reported in the literature, such as toluene steam treatment and thermal cycles of cooling/heating were used to induce <span style=\'font-family:\"Times New Roman\";font-style:italic;language:EN\'>&#946;<span style=\'language:EN\'> phase in amorphous PFO films as well. The exciton dissociation at the interface in films containing TiO<span style=\'language:EN\'>2<span style=\'language:EN\'>/PFO interface were observed by reduction of photoluminescence intensity; and this same efficiency in ultra-thin films is higher than 90%. From these results, it was reported that the exciton migration radius in PFO is (13 <span style=\'font-family:Symbol;language:EN\'>±<span style=\'language:EN\'> 3) nm. Furthermore, effects of excitons annihilation in ultra-thin films were observed in the decay time radiative measurements due to high fluency (~ 10<span style=\'language:EN\'>25<span style=\'language:EN\'> photons/cm<span style=\'language:EN\'>2<span style=\'language:EN\'>s). Finally, in PFO films (with the <span style=\'font-family:\"Times New Roman\";font-style:italic;language:EN\'>&#946;<span style=\'language:EN\'> phase) deposited on the TiO<span style=\'language:EN\'>2 <span style=\'language:EN\'>just the exciton of amorphous regions migrates to the TiO<span style=\'language:EN\'>2<span style=\'language:EN\'> interface, which dissociates them. The thermal energy at room temperature promotes higher efficiency than the exciton dissociation at low temperatures (~ 5 K). However, even at room temperature, the <span style=\'font-family:\"Times New Roman\";font-style:italic;language:EN\'>&#946;<span style=\'language:EN\'> phase molecules act as the most important molecules to capture exciton, competing to the exciton dissociation process. These results conducted to conclude that the energy transfer radius in PFO is equal to (3.5 <span style=\'text-decoration:underline;language:EN\'>+<span style=\'language: EN\'> 0.5) nm. <![if !vml]> <![endif]>

This work describes an experimental investigation of methods of synthesis, determination of structural and physical properties, and analysis and correlation of the properties to the structures of semiconductor quantum dots and quantum dot-polymer hybrid structures. These structures are investigated for applications in flexible solar cell devices. The main synthesis process used in the work was a Laser-Assisted Spray (LAS) process that was developed in our laboratory to deposit surfactant-free PbSe quantum dot (QD) films directly on a substrate. The QD films formed by this technique are in close contact with each other forming a percolation path for charge transport. Analytical instruments that include Atomic Force Microscopy (AFM) and Transmission Electron Microscopy (TEM) were used for structural characterization while optical absorption spectroscopy and photoluminescence were used for determining the quantum confinement of charge carriers in PbSe QDs. In addition, charge transport across lithographically patterned paths was used to determine the transport characteristics and generation of photocurrent in the fabricated structures. Absorption spectroscopy confirmed the quantum confinement of PbSe QDs deposited by LAS deposition. Room temperature current-voltage measurements across a 2 micrometer tunnel junction formed by the QDs produced a power-law dependence of the form I ∝ V2.19 that describes a percolation path of dimensionality slightly above two-dimensional. Absence of surfactants in LAS deposited films improved the conductivity by more than three orders of magnitude. Temperature dependent conductance studies showed thermally activated transport at high temperatures and temperature independent tunneling followed by previously unobserved metallic conduction at low temperatures. The LAS system was successfully modified by incorporating two spray nozzles to transport aerosols of two different precursors, one containing the QDs and the other containing the polymer. This new co-deposition system was successfully used to deposit QDs/Polymer hybrid structures. The TEM and XRD studies of LAS co-deposited films were shown to be uniformly distributed and crystalline. The photo-current experiments of QD/polymer hybrid composites showed clear evidence of enhanced carrier generation and transport as a result of intimate contact between quantum dots (QDs).

No description available.