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Study of optical properties of thin films of perovskiteFAPbBr3 precursors
Smolková, Denisa ; Čech, Vladimír (referee) ; Zmeškal, Oldřich (advisor)
This thesis examines the preparation of thin layers of material for photovoltaic applications with focused on perovskites and determining their optical properties. Basic information about the photovoltaic panels, especially about the perovskites, and the preparation of thin layers is supplied in the theoretical section. This section includes description of optical properties and the main method of study of optical properties, spectroscopic ellipsometry. Experimental section is focused on the preparation of thin layers of perovskites FAPbBr3 and its precursors by spin-coating. Optical properties are evaluated using profilometry, UV VIS spectrometry and spectroscopic ellipsometry. The conclusion summarizes the results of this experiment with focused on comparison of ellipsometric spectrums of perovskites and its precursors.
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Novel diketopyrrolopyrroles for organic photovoltaics
Hrabal, Michal ; Zmeškal, Oldřich (referee) ; Vala, Martin (advisor)
The aim of this diploma thesis is to conduct optical and photovoltaic characterization of derivatives of diketopyrrolopyrrole (DPP) as materials suitable for fabrication of bulk heterojunction organic solar cells. The charge transfer from donor material (DPP) to acceptor material (PCBM) is studied by a quenching of fluorescence. The photovoltaic response is studied by current – voltage characteristic which can tell us crucial parameters such as shor circuit current density Jsc, open circuit voltage Voc, fill factor FF and power conversion efficiency PCE. Optical characterization was carried out for symmetrical DPP derivatives (U69 and U97) which both contained diphenylaminstilbene moiety and differed in N-alkyl group. On the other hand photovoltaic characterization was conducted for analogous but asymmetrical materials (U70 and U99). Material U29 was characterized as well but its properties proved to be very poor. Both these characterizations tell us that materials with shorter solubilization groups (U69 and U99) are more suitable candidates. Achieved PCE for U70 was 0,74 % and for U99 up to 1,39 %. From these values one can say that small molecule organic materials can be used for fabrication of solar cells.
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Focused eletron beam induced deposition
Juřík, Karel ; Zmeškal, Oldřich (referee) ; Pospíšil, Jan (advisor)
Within this work, a set of depositions induced by focused electron beam was prepared. The depositions were prepared in the presence of water vapours from trimethyl(methylcyclopentadienyl)platinum(IV) precursor. The dependence of prepared materials purity on beam accelerating voltage and water vapour pressure was measured. The best platinum content was achieved at (27,2 ± 0,4) at. %, with beam accelerating voltage 5 kV, beam current 1600 pA and water vapour pressure 100 Pa. Due to subsequent long-term exposure to light, air humidity and air oxygen, the platinum content was increased to (39,2 ± 2,1) at. %.
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Sensoric Properties of Organic Materials
Tmejová, Kateřina ; Zmeškal, Oldřich (referee) ; Kratochvílová, Irena (referee) ; Nešpůrek, Stanislav (advisor)
The first part of the work is aimed to the study of changes of electrical properties of substituted phthalocyanines under the influence of humidity. Thin films were prepared by spin coating technique. During the influenece of humidity electrical conductivity increases. Sorption and desorption and the changes in electrical properties under the repated humidity exposure were investigated as well. Impedance spectroscopy was used for the studies. The second part of this work consists of optical studies and changes of optical parametrsunder the influence of different alcohols (methanol, ethanol, 2-propanol) exposures. The investigated samples were prepared by vacuum evaporation a glow-discharge-induced sublimation. The changes of optical reflectances of the films upon exposure to alcoholvapour-containg atmospheres were studied as a function of alcohol concetration and exposure time.
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Study of electrical and dielectric properties of ionic liquids
Maráčková, Lucie ; Nešpůrek, Stanislav (referee) ; Zmeškal, Oldřich (advisor)
This bachelor´s thesis is focused on a study of electrical and dielectric properties of ionic liquids in the form of solution and thin layers. The values of breakdown voltage have been determined from current-voltage characteristics in solutions. Frequency dependencies have been also observed and used for calculation of values of parallel conductivity and capacity of ionic liquid. It was found that solutions is contained by model with one parallel combination of conductivity and capacity. Thin layers have been created by mixing up PEDOT:PSS with two ionic liquids: 1-butyl-3- methylimidazolium trifluoromethanesulfonate and 1-ethyl-3-methylimidazolium tetrafluoroborate. These layers have created electrochemical battery as is evident from current-voltage characteristics. Frequency dependencies are more complex, a model contained two or respectively three parallel conductivities and capacities which have been influenced by PEDOT:PSS and by ionic liquids characteristics.
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Analysis of a-SiOC:H films by selected spectroscopic techniques
Ondreáš, František ; Zmeškal, Oldřich (referee) ; Čech, Vladimír (advisor)
This bachelor thesis deals with preparation of thin plasma polymer films on the basis of tetravinylsilane by plasma-enhanced chemical vapour deposition and film characterization by selected spectroscopic techniques. The theoretical part is a background research about plasma chemistry and spectroscopic methods of characterisation of thin plasma polymer films. The practical part consisted of preparation of two series of samples and their characterization. Prepared thin plasma polymer films were characterized by selected spectroscopic techniques. Thickness and optical constants were determined by spectroscopic elipsometry. Chemical structure was characterized by infrared spectroscopy. The results indicate the possibility of managing physico-chemical properties of thin plasma polymer films on the basis of tetravinylsilane by deposition conditions and thus possibility of preparation materials tailored to a variety of applications.
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Use of biomaterials for optoelectronic applications in semiconductor technology
Čuboň, Tomáš ; Salyk, Ota (referee) ; Zmeškal, Oldřich (advisor)
The bachelor´s thesis is aimed to measurement optical properties of thin layer films of biomaterials which could be used in optoelectronics and semiconductor technology. DNA and BSA were chosen in order to represent such extensive group of biomaterials. The theoretical part describes the way of preparation of thin layer. It also provides some information about basic phenomena and biomaterials. The practical part is focused on the description of preparation of thin layer film using spin-coating method. The chosen materials were studied by optical microscopy, UV-VIS spectrophotometry and spectroscopic ellipsometry. The thickness of prepared samples was measured by mechanic profilometry. In the last section of the bachelor´s thesis, there is discussion and evaluation of results.
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Materials for organic electronics
Skrášek, Martin ; Zmeškal, Oldřich (referee) ; Vala, Martin (advisor)
The work contains literature search on organic electronics, especially organic solar cells. There is described in detail their principle of function and used materials. Also there are mentioned possibilities of synthesis of conjugated systems for this applications and methods of their structural, optical and electrical characterization. In experimental section and discussion is introduced synthesis of five new, various substituted derivates of benzylidenaniline and their characterisation together with another seven derivates, whose synthesis has been described in bachelor thesis. There is investigated influence of substituents to chemical shift of hydrogen on imine bridge and to position of absorption peaks in UV-Vis spectra. There also has been found method for fabrication of thin layers and solar cells with bulk heterojunction have been fabricated. Next, V-A characteristics and impedance spectra of the cells were recorded. According to obtained results, investigated systems act as photodiodes and in case of three derivates the photoinduced increase of electric current has been observed. But for application in solar cells it is necessary to shift the position of absorption spectra towards longer wavelengths.
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Study of emulsion stability by means of physical-chemical and optical methods
Kuchyňová, Jitka ; Veselá, Mária (referee) ; Zmeškal, Oldřich (advisor)
The diploma thesis deals with the stability determination of model O/W (30/70) emulsions at 25°C. In fact, the time and emulsifier concentration (Tego Care PS) dependences of physical properties (aging) were monitored. In the second part of the work, the influence of conservant on emulsion stabilities were studied. In order to study physical properties of emusions rheometry, differential scanning calorimetry (DSC) and optical microscopy were employed. The rheological measurement provided information on viscosity and viscoelastic modulus. DSC experiments used the repeated freezing/thawing cycles which allowed monitoring of changes in crystallization temperature of water present in emulsions and melting enthalpy of ice formed during the cooling. The optical microscopy was used to examine the change in oil droplet size in the course of emulsion destabilization and phase separation. In this case the image analysis was carried out using program HarFA. The results showed that due to the emulsion creaming, the oil droplets diffuse and aggregate which causes phase separation. Those processes were quickest for the emulsion with lowest emulsifier concentration 0.1 % (destabilization during 51 days) The emulsions with emulsifier concentration about 1.5 and 1.3 % were stable at least for 4 months. The presence of the coemulsifiers increased the elastic modulus and descreased the phase difference due to the network formation. It was shown that for the stability determination is necessary to use conservant due to risk of microbial contamination. DSC experiments allowed to distingush samples prepared under different conditions. Lower rotational speed during emulsion preparation caused the appearance of two melting and crystalization peaks while for higher speed only one peak was observed.
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