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Synthetic Exploration of Halide Perovskites and Germanium Semiconductors

Halide perovskites and germanium semiconductors are promising materials for many optical applications such as solar cells and LEDs due to their unique photophysical properties. Compositional substitution and dimensional manipulation can enhance physical or chemical properties of perovskite and germanium semiconductors which in turn promotes their performance in optoelectronic devices. In this thesis, we report the synthetic exploration of composition-control and dimensionality-control of organometal halide perovskite crystals by tuning halide-incorporation and exploiting bulky alkylammonium cations as capping ligands. We also demonstrate a systematic synthesis of all the series of mixed halide perovskite polycrystals and their low dimensional analogues. By optimizing synthetic conditions, we are able to inhibit the appearance of a reversible photoinduced PL peak derived from surface traps. We also synthesize lead-free perovskites for the environmental concerns. Lead is a heavy metal element and its potential toxicity raises concerns for environmental compatibility. To address this problem, we developed a synthetic route to antimony perovskites and germanium perovskites. Surface-bound (CH3)3Sb2I9 layers restrict the growth of CH3NH3PbI3, resulting in CH3NH3PbI3 nanocrystals. Compared to the bulk perovskites, the antimony-capped nanocrystals show stronger photoluminescence. With a direct bandgap of 1.6 eV and a corner-sharing octahedral network crystal structure that are comparable to CH3NH3PbI3, CsGeI3 is potentially promising for photovoltaic applications. To manipulate the optoelectronic properties, we doped high-spin, divalent manganese ions (Mn) into the octahedral Ge sites of CsGeI3. Electron paramagnetic resonance (EPR) helps us better understand the local ion environment and composition of both CsGeI3 and its doped analogue (CsGe1-xMnxI3). Our results expand the lead-free halide perovskite