Structural properties of organometalic halide perovskite and their application in photodetectors

Anastasiia Glushkova
EPFL, 2020
Thèse EPFL

Hybrid organometallic halide perovskites have been intensively investigated in the past years as highly efficient light harvesters for various optoelectronic applications for both sensing and emitting light. However, many open questions remain regarding the crystallization process, environmental impact and implementation of the material into electrical circuits. The central theme of this PhD dissertation is the structural characterization of hybrid organicinorganic perovskites and device fabrication based on these materials. The focus is on methylammoniumlead iodide, CH3NH3PbI3 as one of the most efficient photovoltaic materials. External factors such as temperature, pressure, humidity, etc. affect the materials properties. Thus, it is crucial to study their influence for further applications. In this thesis, it will be shown, that under high pressure (20 GPa) inert gases as Ar and Ne form high-pressure-induced compounds with CH3NH3PbI3. For Ne pressure transmitting media such high-pressure transformation is reversible and the Ne-incorporated compoundis even stable at ambient conditions after decompression. We show that when applying repeated phase transitions during thermal cycling around both 330 and 160 K, CH3NH3PbI3 does not return to the initial state. Instead, at 330 K, the crystal stabilizes an incommensurately modulated tetragonal phase with successive transitions. On the other hand, performing thermal cycling around 160 K generates an increase in the concentration of domains of different phases. In addition, we studied the influence of thermal treatment on the crystal structure in the absence of any phase transition. For that reason, the lower dimensional compound of NH3CH2CH2NH3PbI4 was synthesized and characterized before and after annealing process. We observe and discuss a correlation between photoconductivity and increased disorder. In this work a novel approach of aerosol jet printing deposition of CH3NH3PbI3 has been developed. Making use of intermediate phases of the crystallization process, this deposition method enables the creation of 3D structures of organic-inorganic perovskites on various surfaces. This technique was successfully used in the fabrication of heterostructures based on CH3NH3PbI3 and graphene. Due to large trap-assisted photogain, these heterostructures are very promising for photoconductors. Taking into account the strong X-ray stopping power of the high atomic number Pb and I, devices based on CH3NH3PbI3/graphene heterostructures are excellent for X-ray detection. Such X-ray detectors demonstrate a record high sensitivity value of 2.2 x10^8 uC/(Gy cm^2).

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