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
