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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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Utilization of nanomaterials for organic electronic and photovoltaics
Flimel, Karol ; Žídek, Jan (referee) ; Weiter, Martin (advisor)
The study of the new materials potentially usable for organic photovoltaic and electronics are getting very important from the point of ecological and financial view. Organic electronic devices are getting more and more popular and it is only up to us to search for the new ones that are able to improve their physical properties. The aim of this thesis is to search for materials like have been mentioned above which have very good semiconducting properties. Solutions of pure materials and its mixtures with different concentrations of fullerene have been investigated by ultra-violet spectroscopy, classical fluorescence and time resolved spectrometry. Mainly, were studied the influence of the central atom and side substituents for the optical and electronical properties of our materials of interest. With adding fullerene was observed quenching phenomena of the fluorescence, because all these new materials show usually high photoluminescence. Based on the given results, the most suitable materials had been chosen to provide trial of making organic solar cell, and therefore investigated by the mean of electric measurements (direct current).
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Advanced materials for organic photonics
Zvěřina, Libor ; Salyk, Ota (referee) ; Weiter, Martin (advisor)
The theoretical part of this bachelor’s thesis deals with principles, structure and optimization of organic solar cells and properties of low-molecular advanced materials – diketopyrrolopyrroles, which are used in photovoltaics. In the experimental part six derivatives of diketopyrrolopyrrole were analysed by optical characterisation. It was found that N-substitution does not influence optical properties. Length of conjugated system showed to be the key parameter. The longer conjugation is, the smaller band gap and the greater absorption intensity are obtained. Based on the previous study, four materials were chosen to prepare solar cells. Influence of thermal annealing and gradual-annealing was studied. Current density, fill factor and photovoltaic conversion efficiency were increased by annealing. Gradual-annealing have not lead to further improvement. Finally, solar cells were optimized by 1,8-diiodooctane as an additive. It was found that effect of thermal annealing can be replaced with the additive. The best photovoltaic conversion efficiency was measured on the cell with 0,2 vol. % of additive in active bulk heterojunction.
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Charge carrier transport in organic disordered materials
Češka, Matěj ; Navrátil, Jiří (referee) ; Weiter, Martin (advisor)
This bachelor´s thesis deals with organic materials for use in photovoltaic energy conversion. A theoretical part of this thesis contains brief introduction to organic photovoltaics. Thin organic films were prepared and were characterized by optical methods and by current voltage characteristics. It was found that the light illumination can improve conductivity of prepared thin layers.
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