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13 results on '"Ann, Myung Hyun"'

2. Super-resolution and signal separation in contact Kelvin probe force microscopy of electrochemically active ferroelectric materials

Author

Ziatdinov, Maxim, Kim, Dohyung, Neumayer, Sabine, Collins, Liam, Ahmadi, Mahshid, Vasudevan, Rama K., Jesse, Stephen, Ann, Myung Hyun, Kim, Jong H., and Kalinin, Sergei V.

Subjects
Physics - Applied Physics, Condensed Matter - Materials Science
Abstract

Imaging mechanisms in contact Kelvin Probe Force Microscopy (cKPFM) are explored via information theory-based methods. Gaussian Processes are used to achieve super-resolution in the cKPFM signal, effectively extrapolating across the spatial and parameter space. Tensor matrix factorization is applied to reduce the multidimensional signal to the tensor convolution of the scalar functions that show clear trending behavior with the imaging parameters. These methods establish a workflow for the analysis of the multidimensional data sets, that can then be related to the relevant physical mechanisms. We also provide an interactive Google Colab notebook (http://bit.ly/39kMtuR) that goes through all the analysis discussed in the paper., Comment: Update with accepted version

Published
2020
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6. Exploring Transport Behavior in Hybrid Perovskites Solar Cells via Machine Learning Analysis of Environmental‐Dependent Impedance Spectroscopy

Author

Kim, Dohyung, primary, Muckley, Eric S., additional, Creange, Nicole, additional, Wan, Ting Hei, additional, Ann, Myung Hyun, additional, Quattrocchi, Emanuele, additional, Vasudevan, Rama K., additional, Kim, Jong H., additional, Ciucci, Francesco, additional, Ivanov, Ilia N., additional, Kalinin, Sergei V., additional, and Ahmadi, Mahshid, additional

Published
2021
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7. Exploring Transport Behavior in Hybrid Perovskites Solar Cells via Machine Learning Analysis of Environmental-Dependent Impedance Spectroscopy

Author

Kim, Dohyung, Muckley, Eric S., Creange, Nicole, Wan, Ting Hei, Ann, Myung Hyun, Quattrocchi, Emanuele, Vasudevan, Rama K., Kim, Jong H., Ciucci, Francesco, Ivanov, Ilia N., Kalinin, Sergei V., Ahmadi, Mahshid, Kim, Dohyung, Muckley, Eric S., Creange, Nicole, Wan, Ting Hei, Ann, Myung Hyun, Quattrocchi, Emanuele, Vasudevan, Rama K., Kim, Jong H., Ciucci, Francesco, Ivanov, Ilia N., Kalinin, Sergei V., and Ahmadi, Mahshid

Abstract

Hybrid organic–inorganic perovskites are one of the promising candidates for the next-generation semiconductors due to their superlative optoelectronic properties. However, one of the limiting factors for potential applications is their chemical and structural instability in different environments. Herein, the stability of (FAPbI3)0.85(MAPbBr3)0.15 perovskite solar cell is explored in different atmospheres using impedance spectroscopy. An equivalent circuit model and distribution of relaxation times (DRTs) are used to effectively analyze impedance spectra. DRT is further analyzed via machine learning workflow based on the non-negative matrix factorization of reconstructed relaxation time spectra. This exploration provides the interplay of charge transport dynamics and recombination processes under environment stimuli and illumination. The results reveal that in the dark, oxygen atmosphere induces an increased hole concentration with less ionic character while ionic motion is dominant under ambient air. Under 1 Sun illumination, the environment-dependent impedance responses show a more striking effect compared with dark conditions. In this case, the increased transport resistance observed under oxygen atmosphere in equivalent circuit analysis arises due to interruption of photogenerated hole carriers. The results not only shed light on elucidating transport mechanisms of perovskite solar cells in different environments but also offer an effective interpretation of impedance responses. © 2021 The Authors. Advanced Science published by Wiley-VCH GmbH

Published
2021

11. Phase-Stable CsPbI3 Perovskite Quantum Dots Achieving Near 100% Absolute Photoluminescence Quantum Yield and Applications in Solar Cells

Author

Shen, Qing, primary, kim, Jincheol, additional, Zhang, Yaohong, additional, Hayase, Shuzi, additional, Toyoda, Taro, additional, Liu, Feng, additional, Ding, Chao, additional, Yun, Jae S., additional, Ann, Myung Hyun, additional, Yoon, Sang Eun, additional, Kim, Jong H., additional, and Park, Nochang, additional

Published
2018
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13. Temperature-Dependent Photoluminescence of CH 3 NH 3 PbBr 3 Perovskite Quantum Dots and Bulk Counterparts.

Author

Woo HC, Choi JW, Shin J, Chin SH, Ann MH, and Lee CL

Abstract

Organic-inorganic lead halide perovskite is emerging as a potential emissive material for light emitting devices, such as, light emitting diodes (LEDs) and lasers, which has emphasized the necessity of understanding its fundamental opto-physical properties. In this work, the temperature-dependent photoluminescence of CH 3 NH 3 PbBr 3 perovskite quantum dots (QDs), polycrystalline thin film (TF), and single crystal (SC) has been studied. The optophysical properties, such as exciton-phonon scattering, exciton binding energy, and exciton decay dynamics, were investigated. The exciton-phonon scattering of perovskite is investigated, which is responsible for both PL line width broadening and nonradiative decay of excitons. The exciton binding energy of QDs, TF, and SC were estimated to be 388.2, 124.3, and 40.6 meV, respectively. The observed main exciton decay pathway for QDs is the phonon assisted thermal escape, while that for TF and SC was the thermal dissociation due to low exciton binding energy.

Published
2018
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