Date of Award
Doctor of Philosophy (PhD)
Micro and Nanoscale Systems
Perovskites are a class of semiconductors which has been rapidly growing in popularity due to their potential as absorbing layers for solar cells and applications in other devices such as sensors. There are several types based on the constituent species making up their ABX3 structure, and the flexible formulation results in tunable electronic properties. The research contained within this work aims to contribute to the knowledge of some of the most promising sub-types of halide-containing perovskites by way of first-principles density functional theory calculations, with the aim of improving the commercialization potential of derivative devices. The formulations of (MA)BX3 (A = methylammonium (MA); B = Sn, Pb; X = F, Cl, Br, I) perovskites were systematically studied in the orthorhmobic phase, which are less studied relative to the higher-temperature cubic counterpart. In addition, A = formamadinium (FA) and A = Cs cases are also selected for defect physics studies. For A = MA, structural differences were examined, including lattice geometry and bulk modulus. Thermodynamic stability was calculated, revealing potential stability of the F-containing formulations, previously unreported. It was revealed that the p-orbitals of the halogens determine the valence band levels while those of the B-site metal determine that of the conduction band. Optoelectronic calculations reveal Sn-containing perovskites, more environmentally friendly than the alternative Pb, have smaller band-gaps which results in greater absorbance in the practically-critical visible light range. Motivated by experimental results suggesting FAPbCl3’s potential as an NH3 sensor, defect formation energetics for all possible vacancy, interstitial and antisite defects were calculated. An established GGA exchange-correlation functional was compared with the meta-GGA SCAN functional, finding similar carrier-type (n vs p) predictions and Fermi-pinning defects but with significantly different pinning depth in the band gap. Additionally, ordering of the rotations of the FA ions was found to be critical to defect energetics. All-inorganic CsPbI3’s defect-dependent electronic structure was characterized with and without small gas molecules. It was found that NH3 strongly interacts with deep trap defects, potentially paving the way for a new sensor that has potential applications in processes such as Haber-Bosch, meriting further study. This work serves as a compendium of case studies for the importance of the defect physics in perovskite applications and contributes several hitherto unreported insights on perovskite optoelectronic properties. Finally, appendix A contains a hydrogen storage project completed in which a database of metal hydrides was built and used for machine learning for prediction of formation energy; a web-tool was constructed, with intention for use for high-throughput screening of potential new metal hydride formulations by composition.
Nations, Sean, "" (2023). Dissertation. 995.