Title Nanokristalinių perovskitinių šviesos emiterių elektroninės savybės /
Translation of Title Electronic properties of nanocrystalline perovskite light emitters.
Authors Soriūtė, Vaiva
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Pages 39
Abstract [eng] Hybrid organic–inorganic perovskites are very promising materials for various optoelectronic applications since during a decade solar cells, LEDs, lasers, transistors and photodetectors were created using these compounds. Perovskites have many desirable properties such as solution processibility at low temperatures, high carrier mobility and a tunable bandgap. The energy bandgap tunability can be achieved by mixing cations or exchanging anions and it allows us to manufacture perovskites with different emission and absorption wavelengths which is very useful while fine-tuning designs of LEDs or tandem solar cells. Therefore, mixed cation perovskites require further research to determine optimal composition with the best optoelectronic parameters and to resolve problems of poor stability. The main goal of this work was to manufacture perovskite layers by spin-coating method while gradually changing their cation composition and investigate those samples using various experiments. Time-resolved photoluminescence, integrating sphere and light induced transient grating techniques were employed. Quantum yield, threshold of amplified spontaneous emission, carrier lifetimes and diffusion coefficients were obtained from these measurements. Diffusion coefficient in various samples greatly increased with excitation. This allowed us to conclude that localization-limited diffusion regime was dominant in these perovskites. Carrier lifetimes decreased with growing excitation due to more prominent Auger recombination. Also, samples with more formamidinium in their composition were found to have longer carrier lifetimes. It was attributed to formamidinium ions mitigating ion migration. Diffusion lengths were calculated to be 0,07÷0,3 μm in bromide perovskites. Since they are comparable to layer thickness, we conclude that bromide perovskite layers are of a suitable quality for light emitters. Finally, carrier lifetimes were approximated using carrier transport model. Consequently, radiative and Auger recombination coefficients were determined. They were found to decrease with increasing tolerance factor (it represents reducing part of cesium in compound). These results showed that crystalline lattice of lower symmetry can cause higher recombination rates. Also, obtained bimolecular and Auger recombination coefficients were compared to values available in the literature. Auger recombination coefficients of various samples were in good agreement with them while bimolecular recombination coefficients were higher than those reported. This could be explained by the influence of Coulomb enhanced Auger recombination.
Dissertation Institution Vilniaus universitetas.
Type Master thesis
Language Lithuanian
Publication date 2021