| dc.description.abstract | Metal halide perovskites are a promising class of solution-based semiconductors
with significant potential for optoelectronic devices, including hot carrier solar cells
that are proposed to achieve higher efficiency than conventional solar cells. These
materials possess high light absorption coefficients, long carrier diffusion lengths,
and high defect tolerance, which leads to high power conversion efficiencies in
solar cells. However, the intrinsic material instability of perovskite-based solar
cells limits their performance. Understanding the carrier dynamics and stability
of the material is critical to the development of solar cell physics, particularly
in the case of hot carrier solar cells, as excited carriers with energy greater than
the bandgap energy can potentially generate higher voltage and current than
traditional solar cells. Unfortunately, these hot carriers also tend to rapidly lose
their energy through carrier-phonon scattering, resulting in poor energy conversion.
Perovskites have shown significant potential for hot carrier solar cells in recent
years due to their slow carrier cooling rate. However, a better understanding of
carrier dynamics is critical for developing efficient perovskite-based solar cells.
The effect of changing the different components of perovskite compounds was
studied in a series of metal halide perovskites with varying optical properties
using temperature-dependent photoluminescence, power-dependent photoluminescence,
and ultrafast transient absorption techniques to investigate the carrier
dynamics. The results suggest that the slow cooling of carriers in metal-halide perovskites results from the intrinsic low thermal conductivity of all metal-halide
perovskites. This finding indicates that the phonon energy, exciton binding energy,
and interaction strength have little effect on the cooling of carriers. This study
provides valuable insights into the fundamental understanding of carrier dynamics
in perovskite-based solar cells, which can guide the development of more efficient
and stable devices.
In addition we also studied the presence of hot carriers in a stable metal
halide perovskite system under steady-state conditions. The results showed clear
evidence of hot carriers in the device, but their behavior was strongly dependent
on temperature and competition with photo-induced halide segregation. These
findings provide valuable insights into the behavior of hot carriers in metal halide
perovskite devices for the development of more efficient and stable hot carrier
solar cells.
Finally, our study on the 2D Ruddlesden-Popper perovskite (EPEA)2PbI4 using
temperature and power dependent photoluminescence and transient absorption
spectroscopy showed the presence of multiple excitonic complexes and carrier
redistribution mediated by power and/or temperature. Moreover, we observed
extremely long-lived dark states in transient absorption, which play a significant
role in the photoluminescence and absorption dynamics of (EPEA)2PbI4. These
findings contribute to our understanding of perovskite material behavior and
could aid in the development of more efficient optoelectronic devices. | en_US |
