Optoelectronic properties of mixed iodide-bromide perovskites from first-principles computational modeling and experiment
Journal of Physical Chemistry Letters American Chemical Society 13:18 (2022) 4184-4192
Abstract:
Halogen mixing in lead-halide perovskites is an effective route for tuning the band gap in light emission and multijunction solar cell applications. Here we report the effect of halogen mixing on the optoelectronic properties of lead-halide perovskites from theory and experiment. We applied the virtual crystal approximation within density functional theory, the <i>GW</i> approximation, and the Bethe-Salpeter equation to calculate structural, vibrational, and optoelectronic properties for a series of mixed halide perovskites. We separately perform spectroscopic measurements of these properties and analyze the impact of halogen mixing on quasiparticle band gaps, effective masses, absorption coefficients, charge-carrier mobilities, and exciton binding energies. Our joint theoretical-experimental study demonstrates that iodide-bromide mixed-halide perovskites can be modeled as homovalent alloys, and local structural distortions do not play a significant role for the properties of these mixed species. Our study outlines a general theoretical-experimental framework for future investigations of novel chemically mixed systems.Insights into the charge carrier dynamics in perovskite/Si tandem solar cells using transient photocurrent spectroscopy
Applied Physics Letters AIP Publishing 120:17 (2022) 173504
Abstract:
Direct bandgap perovskite and indirect bandgap Si, which form the two active layers in a tandem solar cell configuration, have different optoelectronic properties and thicknesses. The charge-carrier dynamics of the two-terminal perovskite-on-Si tandem solar cell in response to a supercontinuum light pulse is studied using transient photocurrent (TPC) measurements. Spectral dependence of TPC lifetime is observed and can be classified into two distinct timescales based on their respective carrier generation regions. The faster timescale (∼500 ns) corresponding to the spectral window (300-750 nm) represents the top-perovskite sub-cell, while the slower timescale regime of ∼25 μs corresponds to the bottom-Si sub-cell (>700 nm). Additionally, under light-bias conditions, the transient carrier dynamics of the perovskite sub-cell is observed to be coupled with that of the Si sub-cell. A sharp crossover from the fast-response to a slow-response of the device as a function of the light-bias intensity is observed. These results along with a model based on transfer matrix formulation highlight the role of charge-carrier dynamics in accessing higher efficiencies in tandem solar cells. The carrier transit times and lifetimes in addition to their optical properties need to be taken into account for optimizing the performance.Quantification of Efficiency Losses Due to Mobile Ions in Perovskite Solar Cells via Fast Hysteresis Measurements
Solar RRL Wiley 6:4 (2022)
Utilizing nonpolar organic solvents for the deposition of metal-halide perovskite films and the realization of organic semiconductor/perovskite composite photovoltaics
ACS Energy Letters American Chemical Society 7:2022 (2022) 1246-1254
Abstract:
Having captivated the research community with simple fabrication processes and staggering device efficiencies, perovskite-based optoelectronics are already on the way to commercialization. However, one potential obstacle to this commercialization is the almost exclusive use of toxic, highly coordinating, high boiling point solvents to make perovskite precursor inks. Herein, we demonstrate that nonpolar organic solvents, such as toluene, can be combined with butylamine to form an effective solvent for alkylammonium-based perovskites. Beyond providing broader solvent choice, our finding opens the possibility of blending perovskite inks with a wide range of previously incompatible materials, such as organic molecules, polymers, nanocrystals, and structure-directing agents. As a demonstration, using this solvent, we blend the perovskite ink with 6,6-phenyl-C-61-butyric acid methyl ester and show improved perovskite crystallization and device efficiencies. This processing route may enable a myriad of new possibilities for tuning the active layers in efficient photovoltaics, light-emitting diodes, and other semiconductor devices.A Theoretical Framework for Microscopic Surface and Interface Dipoles, Work Functions, and Valence Band Alignments in 2D and 3D Halide Perovskite Heterostructures
ACS Energy Letters American Chemical Society (ACS) 7:1 (2022) 349-357