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Defects limiting charge collection in semiinsulated CdZnTe
Zajac, Vít ; Franc, Jan (advisor) ; Šikula, Josef (referee)
Title: Defects limiting charge collection in semiinsulated CdZnTe Author: Vít Zajac Department: Institute of Physics of Charles University Supervisor: doc. Ing. Jan Franc, DrSc., Institute of Physics of Charles University Abstract: We achieved to detect photoluminescence transitions deep in the band gap in 4 samples cut from 2 different crystals of semiinsulating Cd1-xZnxTe (x = 0,02 - 0,18) in a row of points along the growth axis. The spectral peaks give evidence of the presence of deep levels in the sample and the intensity of the photoluminescence peaks is to a certain extent proportional to the concentration of these levels. A comparison between resistivity and photoconductivity that were measured by a contact-less method showed that the change of photoluminescence intensity of deep levels does not bring about an unambigous change of neither resistivity nor photoconductivity. Correlation analysis of resistivity and photoconductivity of 6 samples from 4 different crystals confirmed the following model: A shift of the Fermi level within the band gap induced by a change of donor-acceptor compensation is accompanied by an unambigous change of resistivity and results in a change in occupation of the deep levels. This causes a change in the photoconductivity of the crystal because the occupation factor of...
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Centra rekombinace v semiizolačním CdTe
Zázvorka, Jakub ; Franc, Jan (advisor) ; Fiederle, Michael (referee)
Title: Recombination centers in semiinsulating CdTe Author: Jakub Zázvorka Department / Institute: Institute of Physics of Charles University Supervisor of the master thesis: prof. Ing. Jan Franc, DrSc., Institute of Physics of Charles University Abstract: The properties of CdTe for application as a radiation detector are influenced through the presence of deep levels in the bang gap. These energy levels complicate the charge collection and the detector efficiency. Contactless resistivity mapping (COREMA) represents a good option for material characterization without the necessity of metal contacts application. The time-dependent charge measurement was investigated on an adjusted apparatus in FMF Freiburg. Theoretical model of charge transport based on band bending on the sample surface was proposed and a non-exponential behavior was calculated. Using this, the resulted parameter tendencies and their connection with deep level trap or recombination center were explained. A correlation was observed between resistivity, photoconductivity and a near midgap level photoluminescence. Parameter profiles were explained using the theory of Fermi level shift relative to the near midgap level. Three deep levels were observed on samples grown at the Charles University in Prague. Their photoluminescence supports the...
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Organic semiconductors
Tebich, Ivan ; Macháček, Martin (referee) ; Boušek, Jaroslav (advisor)
My final thesis treats of usage photovoltaic phenomenon to production electric energy by solar cells. It inquires into this phenomenon in organic structures. Further it mentions basic types of constructions organic solar cells and evaluates their properties. In experimental part zhe thesis is focused on characterization thin-film structures made out of photoconductiv organic materials.
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Study of organic based structures for solar cells
Kostovčík, Tomas ; Hégr, Ondřej (referee) ; Boušek, Jaroslav (advisor)
Práce se zabývá problematikou využití organických materiálů v solárních článcích. V úvodu práce jsou rozebrány a vysvětleny jednotlivé fyzikální a chemické jevy, které ovlivňují vlastnosti organických materiálů. Práce pokračuje rozborem působení rozličných struktur organických solárních článků na jejich vlastnosti. Dále je popsána technologie výroby vzorku a jsou v ní uvedeny výsledky měření fotovodivosti.
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Low-molecular materials for organic electronics and photonics
Češka, Matěj ; Salyk, Ota (referee) ; Weiter, Martin (advisor)
This master´s thesis deals with organic materials for use in electronics and photonics. Attention was paid to low molecular weight materials. The theoretical part of this thesis contains brief introduction to organic electronics and photonics. In particular, organic transistors, organic solar cells and organic light-emitting diodes are mentioned. The experimental part is focused on study of electrical and optical properties of two types of phthalocyanines. Thin films and solutions of phthalocyanines were characterized by UV-VIS spectroscopy. Thin films were also characterized by current voltage characteristics, spectral response measurement of photocurrent and by method of transient photoconductivity. It was found that illumination affects the electrical properties of thin layers of phthalocyanines, the performance of the prepared thin films depends on the type phthalocyanine and also depends on the thickness of the layer.
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Organic solar cells for photovoltaic conversion of solar energy
Šedina, Martin ; Zmeškal, Oldřich (referee) ; Weiter, Martin (advisor)
This work is focused to study organic materials for solar energy conversion into electricity and characterization of conversion processes. Materials and their blends with semiconducting properties such as photoconductivity were studied. Thin films of organic materials and their blends were prepared by spin-coating method and characterized by optical methods (UV-VIS and photoluminiscence spectroscopy), by current-voltage characteristics, by impedance spectroscopy method, spectral response measurement of photocurrent and method of transient photoconductivity. Structural factors influences the conversion of solar energy into electricity were observed. Based no these results, the materials and their blends useful for photovoltaic applications were determined. The dependence between photoconductivity of thin films and theirs structure was also discussed.
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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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