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| Home > Publications database > Fehlstellendotierung von Eisenoxid- und Bismutsulfid-Nanopartikeln |
| Book/Dissertation / PhD Thesis | FZJ-2018-02119 |
2018
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag
Jülich
ISBN: 978-3-95806-309-9
Please use a persistent id in citations: http://hdl.handle.net/2128/17767
Abstract: In this work semiconducting iron oxide and bismuth sulde nanoparticles are characterized and modied, which should be applied by an innovative solar cell concept as active absorber materials, for example in combination with organic polymers. The advantage of this concept is that the manufacturing process and the optimization of the absorber materials can be separated from the module production. The aim of the present work was to improve the electrical transport properties of hematite ($\alpha$-Fe$_{2}$O$_{3}$) and bismuth sulfide (Bi$_{2}$S$_{3}$) as nanoparticle layers. The focus was on the concept of doping via native point defects. It has been shown that the introduction of defects and the associated doping of the semiconducting nanoparticle layers is a promising approach to tune their electrical transport properties. It was demonstrated for the first time how the electrical conductivity of hematite can be continuously increased by five orders of magnitude through a stepwise temperature treatment (300 - 620 K). This simple method can be applied to hematite in the form of nanoparticle layers as well as in the form of thin layers. By measuring the thermoelectric power, an increase in the charge carrier concentration of about three orders of magnitude was determined. This was attributed to an increasing formation of doping oxygen vacancies and thus to an increasing deviation of the stoichiometric composition of hematite ($\alpha$-Fe$_{2}$O$_{3-x}$ with increasing x). Furthermore, it has been shown that the mobility of the charge carriers is also increased as a result of doping by oxygen vacancies. For the first time, the activation energy of mobility of hematite nanoparticle layers was determined. In the case of nanoparticle layers, a limiting potential barrier between the respective nanoparticles was identified and a picture is proposed for this potential barrier. The height of the potential barrier of the fundamental transport mechanism in the model of the small polaron hopping could be below 0.1 eV. These results are a valuable supplement to the understanding of the charge carrier transport mechanism in hematite. Furthermore, it has been shown that the phase transformation of hematite into magnetite (Fe$_{3}$O$_{4}$) occurs at a vacuum base pressure below 10$^{-6}$ mbar in a temperature range between 597 K and 620 K. This result is in contradiction with the previous stability diagram of iron oxide, in which this phase transformation is expected at a temperature of about 1000 K. In this respect, the results of this work call into question the previous understanding of the temperature of the phase transformation of hematite into magnetite. The native defect doping developed for hematite was transferred to bismuth sulfide nanoparticle layers. In this case, in addition to the introduction of doping sulfur defects, [...]
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