Electricity consumption has been steadily increasing since the beginning of the industrial revolution. Since fossil fuel reserves are limited, researchers are focusing on the search for new, alternative sources, especially renewable ones. Considering that the Sun can produce more energy in one day than humanity consumes in a year, it is surprising that this source of energy is not used more often. The reason for this is the cost of production, given the low efficiencies of electricity conversion achieved by silicon solar cells. Therefore, experts in the photovoltaic field are researching substitutes for silicon solar cells. One of the more promising alternatives are perovskite materials. They were first proposed for photovoltaic purposes only in 2006, and since then their efficiency has increased from 2.2 % to 25.5 % in 2020. The absorption layer in a perovskite solar cell consists of 3D mixed organic-inorganic perovskites with the general formula ABX3. The most studied and used currently is methylammonium lead iodide, CH3NH3PbI3, but due to the toxic nature of lead, the use of other metals is being explored. In addition to the metal, the organic cation in the A site and the halide anion X can be changed. By changing the ions, the crystal structure changes, which affects the electrical and optical properties of the material. However, not all perovskites are suitable for solar cells. The parameters that determine whether a perovskite will be suitable in photovoltaics or not are the tolerance factor and the octahedral factor.
In the master thesis, we focused on the synthesis and characterization of mixed organic-inorganic perovskites, which have an iodide ion at the anionic site. After reviewing the relavant literature and calculating the tolerance and octahedral factors, which were used to verify that an ideal cubic structure would be formed, the synthesis of five different perovskites was done. The synthesis took place in two parts: first, we prepared the organic part, and in the second part, we dissolved it together with the inorganic iodide in the selected solvent. Four of the prepared perovskites had methylammonium iodide at the A site, and GBL solvent was used for dissolution. The last synthesized perovskite had a mixed cation consisting of formamidinium and cesium iodide at the A site, while DMF and DMSO were used as a solvent mixture. The prepared perovskites were characterized using X-ray powder diffraction, single crystal diffraction and optical microscopy. Those perovskites that were successfully synthesized were also tested for UV and thermal stability.
XRD analysis showed that we successfully synthesized both organic precursors, MAI and FAI. From perovskites, the desired product was obtained only in the synthesis of MAPbI3. With the tin analogue, Br crept into the structure, and with the Ca and Cd perovskite, we
had a lot of troubles with the synthesis itself, so we had to somehow adapt it. A new drying method resulted in the MACdI3 perovskite structure, while the Ca analogue resulted in a new, yet unexplored compound. The crystal structure of this compound was successfully determined using single crystal diffraction. In the synthesis of FA0.83Cs0.17PbI3, we did not obtain a homogeneous perovskite, but the product contained two phases.
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