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Rational Design of Semiconductor Heterostructures for Energy Conversion
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Increasing worldwide energy consumption has imposed strain on natural energy sources and given rise to an energy crisis on our society. The development of efficient solar energy conversion to augment other renewable energy approaches is one of the grand challenges in our time. Water splitting, or the disproportionation of Hv2O into energy‐dense fuels, Hv2 and Ov2, is undoubtedly a promising strategy. However, solar water splitting has been a long challenge in the scientific community since the process involves the concerted transfer of four electrons and four protons, which requires the synergistic operation of solar light harvesting, charge separation, mass and charge transport, and redox catalysis processes. In the first thrust, we explore the development of tunable and programmable heterostructures comprised of MvxVv2Ov5 nanowires (where M = Pb^2+, Sn^2+) and cadmium chalogenide quantum dots (QDs: CdS, CdSe, and CdTe) designed to extract photoexcited holes from the valence band of quantum dot to mid-gap state of MvxVv2Ov5 nanowires to facilitate water oxidation at low overpotentials. Thermodynamic energetic band offsets and the relative band alignment of MxV2O5/QD heterostructures have been studied by hard X-ray photoelectron spectroscopy and density functional theory, whereas the dynamics of charge transfer kinetics has been examined by ultrafast transient absorption spectroscopy. These heterostructures demonstrate the remarkable utility of stereoactive lone pairs of post-transition-metal (p-block) cations in mediating solar energy conversion by dint of precise tunability of their energy positioning. In the second thrust, we develop an alternative palette of light harvesting semiconductors through the establishment of dimensional control over lead halide perovskites. The nucleation and growth processes are finely tuned with the help of added surface ligands in order to precisely control size and thus optical properties of the nanocrystals. Dimensional control is a key to engineering optical, electronic, and magnetic properties of materials owing to quantum confinement effects, selective elimination of symmetry elements, and the pronounced role of surface energy. Utilizing ligand-mediated synthetic approaches, such as ligand-assisted reprecipitation and hot colloidal methods, allows for control over nucleation/growth kinetics and consequently enables precise modulation of nanocrystal dimensions. In this dissertation, we have been successful at synthesizing precisely tunable 2D methylammonium lead bromide (MAPbBr3) nanoplatelets by controlling the surface-capping ligands. Utilizing a variety of spectroscopic tools, we have derived mechanistic understanding and structure— function correlations of the role of surface-capping ligands in mediating the growth of all-inorganic 2D CvsPbBrv3 nanoplatelets as a function of reaction temperature and concentration.
lead halide perovskite
Cho, Junsang (2018). Rational Design of Semiconductor Heterostructures for Energy Conversion. Doctoral dissertation, Texas A & M University. Available electronically from