Kyoto University (京都大学) / 0048 / 新制・課程博士 / 博士(工学) / 甲第19007号 / 工博第4049号 / 新制||工||1623 / 31958 / 京都大学大学院工学研究科高分子化学専攻 / (主査)教授 伊藤 紳三郎, 教授 赤木 和夫, 教授 辻井 敬亘 / 学位規則第4条第1項該当

Due to their unique properties organic semiconductors may be used for various applications in organic optoelectronic devices: light emitting devices, lasers, field-effect transistors, photovoltaic cells and etc. Despite high perspectives of organic semiconductors they are still upstaged by their inorganic counterparts. Development of organic electronics requires better understanding of electrooptical properties of organic semiconductors and relationships between their structure and functions. The main goal of this thesis is a detailed investigation of ultrafast exciton and charge carrier processes in pure organic semiconductors and their blends with fullerene derivatives. Investigated organic or silicon organic semiconductors were poly-di-n-hexylsilane (PDHS), polyfluorenes F8BT and PSF-BT, merocyanine MD376. C60 fullerene and its derivative PCBM were used in blends. Ultrafast transient absorption, fluorescence, and integral mode photocurrent measurements were used for investigations. The investigation of PDHS nanocomposites revealed that PDHS incorporation into nanopores can be used for improvement of fluorescence properties. Formation of intramolecular charge transfer state was proposed for PSF-BT neat films. Charge transfer scheme of the formation of long-lived charge pair state in PSF-BT/PCBM blend was presented. The charge pair and free charge carrier generation scheme in merocyanine blends with fullerene derivatives were discussed in detail. Analysis of measurement... [to full text] / Dėl savo unikalių savybių organiniai puslaidininkiai gali būti plačiai pritaikyti įvairiuose optoelektroniniuose prietaisuose: organiniuose šviestukuose, organiniuose lazeriuose, organiniuose tranzistoriuose ir organiniuose šviesos elementuose. Visi šie pritaikymai yra galimi dėl organinių molekulių laidumo. Nepaisant didelių organinių puslaidininkių perspektyvų, jie vis dar yra nukonkuruojami neorganinių puslaidininkių. Pagrindinis šių tezių tikslas yra detaliai ištirti eksitonų ir krūvininkų dinamikos procesus grynuose organiniuose puslaidininkiuose ir jų mišiniuose su fulereno dariniais. Buvo matuoti organiniai ir silicio organiniai puslaidininkiai: poli-di-n-heksilsilanas (PDHS), polifluoreno dariniai F8BT ir PSF-BT, merocianinas MD376. Mišiniuose naudoti fulerenai buvo C60 ir jo darinys PCBM. Tyrimams buvo naudoti ultraspartūs skirtuminės sugerties, fluorescencijos ir integralinės fotosrovės matavimai. PDHS tyrimai atskleidė, kad neorganinės matricos sumažina nespindulinį relaksacijos kanalą. PDHS nanokompozitai gali būti naudojami polimero fluorescencijos savybių: stabilumo, kvantinio našumo pagerinimui. Polifluorenų F8BT ir PSF-BT grynų plėvelių tyrimų metu nustatyti eksitonų-eksitonų anihiliacijos ir eksitonų migracijos skirtumai. Vidumolekulinės krūvio pernašos būsenos formavimasis buvo pasiūlytas PSF-BT grynoms plėvelėms. Pristatyta ilgi gyvuojančių krūvininkų porų formavimosi schema PSF-BT/PCBM mišiniuose. Krūvio pernašos būsenų formavimasis buvo ištirtas... [toliau žr. visą tekstą]

Dėl savo unikalių savybių organiniai puslaidininkiai gali būti plačiai pritaikyti įvairiuose optoelektroniniuose prietaisuose: organiniuose šviestukuose, organiniuose lazeriuose, organiniuose tranzistoriuose ir organiniuose šviesos elementuose. Visi šie pritaikymai yra galimi dėl organinių molekulių laidumo. Nepaisant didelių organinių puslaidininkių perspektyvų, jie vis dar yra nukonkuruojami neorganinių puslaidininkių. Pagrindinis šių tezių tikslas yra detaliai ištirti eksitonų ir krūvininkų dinamikos procesus grynuose organiniuose puslaidininkiuose ir jų mišiniuose su fulereno dariniais. Buvo matuoti organiniai ir silicio organiniai puslaidininkiai: poli-di-n-heksilsilanas (PDHS), polifluoreno dariniai F8BT ir PSF-BT, merocianinas MD376. Mišiniuose naudoti fulerenai buvo C60 ir jo darinys PCBM. Tyrimams buvo naudoti ultraspartūs skirtuminės sugerties, fluorescencijos ir integralinės fotosrovės matavimai. PDHS tyrimai atskleidė, kad neorganinės matricos sumažina nespindulinį relaksacijos kanalą. PDHS nanokompozitai gali būti naudojami polimero fluorescencijos savybių: stabilumo, kvantinio našumo pagerinimui. Polifluorenų F8BT ir PSF-BT grynų plėvelių tyrimų metu nustatyti eksitonų-eksitonų anihiliacijos ir eksitonų migracijos skirtumai. Vidumolekulinės krūvio pernašos būsenos formavimasis buvo pasiūlytas PSF-BT grynoms plėvelėms. Pristatyta ilgi gyvuojančių krūvininkų porų formavimosi schema PSF-BT/PCBM mišiniuose. Krūvio pernašos būsenų formavimasis buvo ištirtas... [toliau žr. visą tekstą] / Due to their unique properties organic semiconductors may be used for various applications in organic optoelectronic devices: light emitting devices, lasers, field-effect transistors and photovoltaic cells and etc. Despite high perspectives of organic semiconductors they are still upstaged by their inorganic counterpart. The efficiency of electrooptical properties of organic semiconductors is tried to increase. The main goal of this thesis is a detailed investigation of ultrafast exciton and charge carrier processes in pure organic semiconductors and their blends with fullerene derivatives. Measured organic or silicon organic semiconductors were poly-di-n-hexylsilane (PDHS), polyfluorenes F8BT and PSF-BT, merocyanine MD376. Fullerenes used in blends were C60 and its derivative PCBM. Ultrafast transient absorption, fluorescence, and integral mode photocurrent measurements were used for investigations. The investigation of PDHS revealed that PDHS nanocomposites can be used for improvement of neat PDHS films fluorescence properties. The formation of intramolecular charge transfer state was proposed for PSF-BT neat films. Charge transfer scheme of the formation of long-lived charge pair state in PSF-BT/PCBM blend was presented. The formation of charge transfer states was explored in neat merocyanine films and blends with fullerene derivatives. The scheme of generation of charge pairs and free charge carriers in merocyanine blends with fullerene derivatives was discussed in... [to full text]

No description available.

La photocatalyse se base sur l’excitation d’un semi-conducteur par des photons d’énergie supérieure ou égale à son gap, générant des paires électron-trous. Celles-ci sont très réactives et susceptibles de réagir à l’interface pour réaliser par exemple l’oxydation totale d’un composé organique. Cette méthode peut être appliquée sur des eaux usées pour éliminer totalement les polluants organiques qui y sont présents. Dans la perspective d’une utilisation du soleil comme source de lumière, cette méthode peut s’avérer très économique et écologique pour le traitement de l’eau.L’interaction lumière-semi-conducteur et la dynamique des porteurs de charge sont des processus physico-chimiques primordiaux pour la photocatalyse, et il est nécessaire de bien les comprendre pour maîtriser le procédé et développer des matériaux plus efficaces. La Time Resolved Microwave Conductivity (TRMC) est une technique qui se base sur la réflexion des micro-ondes sur un semi-conducteur excité qui est directement reliée avec le nombre de porteurs de charge photo-générés. Il s’agit d’un moyen de sonder en temps réel la dynamique des porteurs de charge dans les semi-conducteurs.Ce travail s’inscrit dans le cadre du projet ANR PhotoNorm. Il consiste en une étude par TRMC de dioxyde de titane TiO2 utilisé pour la dépollution de l’eau par photocatalyse. Une partie de cette étude concerne la caractérisation des propriétés opto-électroniques des matériaux, pour lesquels la dynamique des porteurs de charge sera comparée à l’activité photocatalytique. L’effet bénéfique en photocatalyse de la déposition de nanoparticules d'or, d'argent ou bimetallique or-cuivre sur des TiO2 commerciaux sera relié à une capture d’électrons libres observée en TRMC. L’effet bénéfique sur la photocatalyse en lumière visible a été relié à une injection d’électrons dans le TiO2 par des nanoparticules de bismuth. L’autre partie de ce travail consiste en une étude plus fondamentale de la dynamique des porteurs de charge dans des TiO2 commerciaux ou synthétisés dans le cadre du projet PhotoNorm. Il y sera montré l’importance de la longueur d’onde et de l’intensité d’excitation du matériau sur le rendement de génération de porteurs de charge. L’importance des effets de surface et de l’environnement seront aussi mis en évidence de plusieurs façons. La première consiste simplement en un traitement chimique de la surface (lavage), qui peut avoir une grande influence à la fois sur la dynamique des porteurs de charge et sur la photocatalyse, sûrement en lien avec la présence d’impuretés de surface. La seconde consiste à imprégner le TiO2 par des colorants organiques présentant une forte absorption en lumière visible. Les mesures de TRMC sur ces systèmes permettent de mettre en évidence l’interaction entre le semi-conducteur et les molécules extérieures adsorbées à sa surface, notamment l’injection d’électrons du colorant excité vers le semi-conducteur, mais aussi des effets de recombinaison accrus. La troisième méthode consiste à modifier l’atmosphère de travail en TRMC. Il y est observé notamment l’importance de l’oxygène sur la dynamique des porteurs de charge, et notamment les effets de captures d’électrons, phénomènes qui entrent en jeu dans le processus de photocatalyse.Au final, la TRMC s’avère être un bon moyen d’étude de la durée de vie des porteurs de charge dans les semi-conducteurs, qui peut permettre de mieux comprendre les processus fondamentaux associés à la photocatalyse. / The photocatalysis is based on the excitation of semiconductor by photons with an energy superior or equal to the gap, generating electron-hole pairs. These are very reactive and able to react at the interface, involving for exemple the total oxidation of an organic compound. This method can be used on wastewater to eliminate the organic pollutants. With a view to use the sun as a light source this method may become an economical and ecological way for the water treatment. Light interaction between light and semiconductor and the charge-carrier dynamics are fundamental processes for photocatalysis and it is necessary to understand them in order to manage with this process and develop more efficient materials. The Time Resolved Microwave Conductivity (TRMC) is a method based on the reflexion of microwaves on an excited semiconductor which is linked to the number of photo-generated charge-carriers. This method allows us to probe in real time the charge-carrier dynamics in semiconductor. This work is included in the ANR Photonorm project. It consists in a TRMC study on titanium dioxyde TiO2 used for water depollution by photocatalysis. One part of this study consists in the characterization of the opto-electronic properties of materials for which the charge-carrier dynamics will be compared with the photocatalytic activity. The beneficial effect of nanoparticles deposition of gold, silver or gold-copper bimetallics on commercial TiO2 will be linked to the observation of free electrons observed by TRMC . The beneficial effect on photocatalysis in visible light was linked to an electron injection in TiO2 by bismuth nanoparticles. The second part of this work consists in a more fundamental study of charge-carrier dynamics on commercial or synthetized for the Photonorm project. I will be shown the importance of excitation wavelength and intensities on charge carrier generation. The importance of surface effect and environment will be emphasized by several ways. The first one just consist in surface treatment which can have a major importance on charge-carrier dynamics and photocatalysis, probably in connection with the presence or not of impurities on the surface. The second way consists in impregnating TiO2 by organic dyes which show a strong visible light absorption. The TRMC measurements highlight the interaction between the adsorbed molecules and the semiconducteur, including the electron injection from the excited dye to the TiO2 but also an increased recombination effect. The third method consist in modified the working atmosphere in TRMC. The major role of oxygen is so observed on charge-carrier dynamics, with an effect of electron capture, involving in photocatalytic mechanism.Finally TRMC proves to be a convenient method for studying charge-carrier dynamics in semiconductors, which allow a better understanding of fundamental processes bound to photocatalysis.

The developement of a femtosecond-time-resolved spectroscopic ellipsometry setup based on a pump-probe technique is described. The characterization of the setup is presented as well as first results of experiments on a c-plane oriented ZnO thin film are shown. Indications for the study of fast charge-carrier dynamics are given.:Introduction 1 1 Theoretical framework 3 1.1 Zinc oxide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1.1 Crystal and band structure . . . . . . . . . . . . . . . . . . . . . 3 1.1.2 Excitons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 1.2 Dielectric function and electronic transitions . . . . . . . . . . . . . . . . 5 1.2.1 Electronic transitions . . . . . . . . . . . . . . . . . . . . . . . . . 5 1.2.2 Dielectric function . . . . . . . . . . . . . . . . . . . . . . . . . . 5 1.3 Charge carrier dynamics . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 1.3.1 High excitation effects . . . . . . . . . . . . . . . . . . . . . . . . 8 1.3.2 Charge carrier density-dependent dielectric function model . . . . 9 1.4 Light polarization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 2 Preliminary experiments 14 2.1 Methods and instrumentation . . . . . . . . . . . . . . . . . . . . . . . . 14 2.2 Setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 2.3 Experimental challenges . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 2.4 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 2.4.1 Time-integrated micro-ellipsometry . . . . . . . . . . . . . . . . . 28 2.4.2 Time-resolved ellipsometry . . . . . . . . . . . . . . . . . . . . . . 31 2.4.3 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 3 Conclusive experiments at ELI Beamlines 35 3.1 Setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 3.2 Samples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48 3.3 Demonstration of functionality . . . . . . . . . . . . . . . . . . . . . . . . 49 3.3.1 Time-resolved reflectometry . . . . . . . . . . . . . . . . . . . . . 49 3.3.2 Time-resolved ellipsometry . . . . . . . . . . . . . . . . . . . . . . 51 4 Results and discussion 55 4.1 Time-resolved reflectometry . . . . . . . . . . . . . . . . . . . . . . . . . 55 4.2 Time-resolved ellipsometry . . . . . . . . . . . . . . . . . . . . . . . . . . 60 5 Summary and outlook 63

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第19007号 / 工博第4049号 / 新制||工||1623(附属図書館) / 31958 / 京都大学大学院工学研究科高分子化学専攻 / (主査)教授 伊藤 紳三郎, 教授 赤木 和夫, 教授 辻井 敬亘 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

No description available.

Dye-sensitized solar cells (DSSCs) and perovskite solar cells are emerging as promising potential low-cost alternatives to established crystalline silicon photovoltaics. Of the employed functional materials, however, many fundamental optoelectronic properties governing photovoltaic device operation are not sufficiently well understood. This thesis reports on a series of studies using ultrafast THz and photoluminescence spectroscopy on two classes of such materials, providing insight into the dynamics of charge-transport and recombination processes following photoexcitation. For TiO₂-nanotubes, which have been proposed as easy-to-fabricate electron transporters for DSSCs, fast, shallow electron trapping is identified as a limiting factor for efficient charge collection. Trapping lifetimes are found to be about an order of magnitude shorter than in the prevalently employed sintered nanoparticles under similar excitation conditions and trap saturation effects are not observed, even at very high excitation densities. In organo-lead halide perovskites - specifically CH₃NH₃PbI₃ and CH₃NH₃PbI_3-xCl_x, which have only recently emerged as highly efficient absorbers and charge transporters for thin-film solar cells, carrier mobilities and fundamental recombination dynamics are revealed. Extremely low bi-molecular recombination rates at least four orders of magnitude below the prediction of Langevin's model are found as well as relatively high charge-carrier mobilities in comparison to other solution-processable materials. Furthermore a very low influence of trap-mediated recombination channels was observed. Due to a combination of these factors, diffusion lengths reach hundreds of nanometres for CH₃NH₃PbI₃ and several microns for CH₃NH₃PbI_3-xCl_x. These results are shown to hold for both, solution processed and vapour-deposited CH₃NH₃PbI_3-xCl_x and underline the superb suitability of the materials as absorbers in solar cells, even in planar heterojunction architectures. The THz-frequency spectrum of the conductivity of the investigated perovskites is consistent with Drude-like charge transport additionally exhibiting weak signatures of phonon coupling. These coupling effects are also reflected in the luminescence of CH₃NH₃PbI_3-xCl_x, where they are believed to be the cause of the observed homogeneous spectral broadening. Further photoluminescence measurements were performed at temperatures between 4 K and room temperature to study the nature of recombination pathways in the material.

No description available.