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Access Type
WSU Access
Date of Award
January 2022
Degree Type
Dissertation
Degree Name
Ph.D.
Department
Chemistry
First Advisor
Zhenfei Liu
Abstract
The research projects in this thesis are focused on the understanding of the complexscreening effect at heterogeneous interfaces. Heterostructures formed between two different semiconductors can be of great importance in electronic and opto-electronic applications owing to the difference in energy levels with respect to the work-functions of the electrodes. However, the underlying physical mechanisms that govern the electronic and optical responses of these heterostructures are not well-understood, especially the comprehensive description of the structure-property relationship at the atomistic level, which can be very difficult to obtain via experimental studies. In chapter 3, the effect of the number of P3HT layers on the electronic structure of the P3HT:PCBM interface is studied by means of first-principles GW. We apply the substrate screening approach to accelerate such calculations and to better understand the many-body dielectric screening at the interface. The quasiparticle band gap of the entire interface is found to decrease as the number of P3HT layers increases. The gaps of the individual components of the interface are found to be smaller than those of their isolated counterparts, with strong dependence on the number of P3HT layers. Importantly, when comparing the P3HT:PCBM system, where a single interface is present, and the P3HT:PCBM:P3HT system, where an interface is formed on either side of PCBM, we find that the two systems exhibit very different quasiparticle energy level alignments. We discuss the possible implications of our findings in related experiments. The results from this chapter provide computational insight into energy conversion pathways in these materials. In chapter 4, we investigate the modulation of the electronic properties of two important electron-rich molecules by several transition metal dichalcogenide substrates, We employ the first-principles substrate screening GW approach to quantitatively characterize the quasiparticle electronic structure of a series of interfaces: metal-free phthalocyanine (H2Pc) adsorbed on monolayer MX2 (M=Mo, W; X=S, Se) and zinc phthalocyanine (ZnPc) adsorbed on MoX2 (X=S, Se). Furthermore, we reveal the dielectric screening effect of the commonly used α-quartz (SiO2) substrate on the H2Pc:MoS2 interface, using the dielectric embedding GW approach. The results from this chapter furnish the first set of GW results for these interfaces, providing structure-property relationships across a series of similar systems and benchmarks for future experimental and theoretical studies. In Chapter 5, we focus on the effect of a commonly used substrate in experiments – hexagonal boron nitride – on three systems: monolayer MoS2, bilayer MoS2, and the MoS2/WS2 heterostructures. To reduce the computational cost, we employ the first-principles dielectric embedding GW to capture the dielectric effect of the substrate, which leads to a quantitative agreement with existing experiments. We further discuss the local field effect in the energy renormalization at the interface. The results from this chapter explain the effect of substrate orientation on the screening effect at heterogeneous interface, and the implications of the dielectric environment of commonly used substrates in experimental measurements. The results from these studies provide useful information on the complex interactions in heterogeneous systems, viz-a-viz the unraveling of the renormalization of the energy levels at the interface which is crucial to charge transfer dynamics in complex heterostructures.
Recommended Citation
Adeniran, Olugbenga Matthew, "Quasiparticle Electronic Structure And Optical Excitation Of Weakly Coupled Heterostructures From A First-Principles Gw-Bse Approach" (2022). Wayne State University Dissertations. 3746.
https://digitalcommons.wayne.edu/oa_dissertations/3746