<p>Technological advancements in
electronics industry are driven by innovations in device fabrication techniques
and development of novel materials. Halide perovskites are one of the latest
additions to the semiconductor family. The performance of solid-state devices
based on halide perovskites is now competing with other well-established
semiconductors like silicon and gallium arsenide. However, the intrinsic
instability of three-dimensional (3D) perovskites poses a great challenge in
their widespread commercialization. The soft crystal lattice of hybrid halide
perovskites facilitates anionic diffusion which impacts material stability,
optoelectronic properties, and solid-state device performance.</p>
<p>Two-dimensional (2D) halide
perovskites with organic capping layers have been used for improving the
extrinsic stability as well as suppressing intrinsic anionic diffusion.
Nevertheless, a fundamental understanding of the role of compositional tuning,
especially the impact of organic cations, in inhibiting anionic diffusion
across the perovskite-ligand interface is missing. In our research, we first
developed a library of atomically sharp and flat 2D heterostructures between
two arbitrarily determined phase-pure halide perovskite single crystals. This
platform was then used to perform a systematic investigation of anionic
diffusion mechanism and quantify the impact of structural components on anionic
inter-diffusion in halide perovskites. </p>
<p>Stark differences were observed in
anionic diffusion across 2D halide perovskite lateral and vertical
heterostructures. Halide inter-diffusion in lateral heterostructures was found
to be similar to the classical Fickian diffusion featuring continuous
concentration profile evolution. However, vertical heterostructures show a
“quantized” layer-by-layer diffusion behavior governed by a local free energy
minimum and ion-blocking effects of the organic cations. For both lateral and
vertical migrations, halide diffusion was found to be faster in perovskites
with larger inorganic layer thickness. The increment becomes less apparent as
the inorganic layer thickness increases, akin to the quantum confinement effect
observed for band gaps. Furthermore, we found that bulkier and more rigid
π-conjugated organic cations inhibit halide inter-diffusion much more
effectively compared to short chain aliphatic cations. These results offer
significant insights into the mechanism of anionic diffusion in 2D perovskites
and provide a new materials platform for heterostructure assembly and device
integration.</p>
| Identifer | oai:union.ndltd.org:purdue.edu/oai:figshare.com:article/19521823 |
| Date | 20 April 2022 |
| Creators | Akriti (12355252) |
| Source Sets | Purdue University |
| Detected Language | English |
| Type | Text, Thesis |
| Rights | CC BY 4.0 |
| Relation | https://figshare.com/articles/thesis/Anion_Diffusion_in_Two-Dimensional_Halide_Perovskites/19521823 |
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