Doctor of Philosophy (PhD)
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Organic-inorganic halide perovskite, nanocrystals, photovoltaic
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A great challenge facing humanity in the 21st century is finding inexhaustible and inexpensive energy sources to power the planet. Renewable energies are the best solutions because of their abundance, diversity, and pollution-free emission. Solar energy is the cleanest and most abundant renewable energy source available. In the continuing quest for efficient and low-cost solar cells, perovskite solar cells (PSCs) have emerged as a potential replacement for silicon solar cells. Since 2009, the record efficiencies of PSCs have been skyrocketing from 3.8 % to 25.2 % and are now approaching the theoretical limit. Along with the three-dimensional perovskites used for photovoltaics, the layer-structured perovskites also attracted significant attention due to their remarkable optoelectronic properties for application in lasing and light-emitting devices.
In this dissertation, the synthesis of two-dimensional (C6H5C2H4NH3)2PbBr4 (PEPB) nanocrystal with thickness as few as 3 unit cell layers was demonstrated. Compare to its bulk crystals, 2D PEPB nanocrystals exhibited a major blue-shifted photoluminescence (PL) peak at 409 nm, which is attributed to the quantum confinement effect, and two new PL peaks at 480 and 525 nm at room temperature. Time-resolved reflectance spectroscopy was used to investigate the exciton dynamics, exhibiting an exciton lifetime of 16.7 ps. The high-quality 2D PEPB nanocrystals are expected to have high PL quantum efficiency and potential applications for light-emitting devices.
In the second part, the optimization of planar PSCs is carried out by the engineering of the deposition method for MAPbI3 thin films. We compared the quality of the MAPbI3 films deposited by two different methods. Compared to the film deposited by the Lewis adduct method, perovskite film deposited by the methylamine-gas-assisted method showed larger crystal grains, smoother surface morphology, and a preferred (110) crystal orientation. As for PSC efficiency, the methylamine-gas-assisted method also showed clear advantages over the Lewis adduct method (highest efficiency: 19.28 % vs. 18.17 %; average efficiency: 16.28 % vs. 12.59 %). The methylamine-gas-assisted method, with its potential for upscaling, is no doubt a noteworthy leap towards the roll-to-roll printing of large-area PSCs.
Previously Published In
Guo, R.; Zhu, Z.; Boulesbaa, A.; Hao, F.; Puretzky, A.; Xiao, K.; Bao, J.; Yao, Y.; Li, W., Synthesis and photoluminescence properties of 2D phenethylammonium lead bromide perovskite nanocrystals. Small Methods, 2017, 1 (10), 1700245.
Guo, R.; Li, W., Perovskite Nanomaterials for solar cells. iScience Notes, 2019, 2.
Yang, M.; Guo, R.; Kadel, K.; Liu, Y.; O'Shea, K.; Bone, R.; Wang, X.; He, J.; Li, W., Improved charge transport of Nb-doped TiO2 nanorods in methylammonium lead iodide bromide perovskite solar cells. J. Mater. Chem. A, 2014, 2, 19616-19622.
Rong, Y.; Venkatesan, S; Guo, R.; Wang, Y.; Bao, J.; Li, W.; Fan, F; Yao, Y., Critical kinetic control of non-stoichiometric intermediate phase transformation for efficient perovskite solar cells. Nanoscale, 2016, 8, 12892-12899.
Guo, Rui, "Organic-Inorganic Halide Perovskite Nanocrystals and Solar Cells" (2020). FIU Electronic Theses and Dissertations. 4582.
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