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J. Wang:
"Synthesis and Characterization of Novel Inorganic-Organic Hybrids for Photocatalytic H2 Evolution and Photovoltaic Applications";
Betreuer/in(nen), Begutachter/in(nen): D. Eder, F. Kleitz, K. Föttinger; Institut für Materialchemie, 2019.

My PhD project focused on the development of advanced materials for solar energy conversion. Compared with their component materials, hybrid materials additionally offer synergistic effects, such as efficient charge separation, and thus have attracted great interest. In this thesis, I investigated two types of organic-inorganic hybrid materials, i.e. metal-organic frameworks (MOFs) and hybrid organic inorganic perovskites (HOIP), for photocatalytic hydrogen production and photovoltaic electricity generation.
The first part of my thesis investigated the influence of the organic ligand in MOFs on the materials structure, functional properties and photocatalytic performance. In particular, I designed mixed-ligand Ti-based MOFs, MIL1-x(NH2-MIL)x-125-Ti with varying ligand composition. The MOFs were characterized with a wide range of state-of-the-art techniques, including XRD, SEM, DRS, FT-IR, TGA, physisorption. The results show that the different ligands were homogeneously distributed over the entire framework, affected the pore width, but did not alter the crystal structure. Photocatalytic studies demonstrate that the hydrogen evolution rate of the mixed-ligand MOFs decreased with increasing amount of NH2-ligand. Photoluminescence and absorption spectroscopies revealed that this can be attributed to a higher charge recombination probability in presence of NH2-ligand. Furthermore, I observed that methanol constitutes the better hole scavenger for Ti-MIL, while triethanolamine is preferable for NH2-containing MOFs. Another highlight of this work was the discovery that the reduced Ti-species (Ti3+) in the Ti-MIL can be preserved in oxygen-free aqueous solution for up to at least 45 minutes and utilized for water/alcohol reduction on demand upon the addition of hexachloro-platinic acid. This unprecedented behavior of essentially a "conceptual light battery" will stimulate great interest in the community.
In the second part I studied the thermal stability of MOFs and their conversion into nanostructured metal oxides. This barely investigated calcination process has yielded highly-porous, defect-rich TiO2-x particles with large specific surface areas, which demonstrated greatly enhanced photocatalytic properties when compared to the benchmark P25-TiO2.
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The third part of this thesis dealt with the photovoltaic performance of HOIP in perovskite solar cells (PSCs). I modified the PSC fabrication process and investigated different solar cells configurations and preparation routes of perovskite, in particular I developed a two-step process to anneal the photoactive film (i.e. `curing´) that led to fewer defects/grain boundaries and improved power conversion efficiencies. Moreover, the work with the collaborators was among the first to prepare Bi-based PSCs that manifest a superior air-stability and moisture stability, albeit with rather low power conversion efficiencies.