| Author: | Zhong, Cenchen |
| Title: | Structural and photoluminescence responses of two-dimensional hybrid perovskite nanoflakes under UV-light illumination |
| Advisors: | Zhu, Ye (AP) |
| Degree: | M.Phil. |
| Year: | 2023 |
| Subject: | Hybrid perovskites Hong Kong Polytechnic University -- Dissertations |
| Department: | Department of Applied Physics |
| Pages: | xiii, 88 pages : color illustrations |
| Language: | English |
| Abstract: | Two-dimensional (2D) organic-inorganic hybrid perovskites have recently emerged as a promising class of optoelectronic materials for various applications, such as solar cells, lasers, and photodetectors. Compared with their three-dimensional (3D) counterparts, 2D perovskites exhibit superior moisture resistance due to their layered structure, wherein inorganic layers are sandwiched by hydrophobic organic layers. Since the optoelectronic applications of perovskite materials often operate under challenging environments involving light exposure, it is crucial to conduct comprehensive studies on the photo-stability of these materials. Until now, the majority of photo-stability studies have been concentrated on 3D perovskites, with limited research on the effect of light on 2D perovskites and the underlying mechanism. Thus, from both application and fundamental standpoints, it is crucial to develop a comprehensive understanding of the influence of light on structure and properties of 2D perovskites. Such knowledge is essential to enhance the longevity of 2D perovskite-based devices and effectively tailor their photophysical properties. In this work, a type of 2D perovskites with a chemical formula as (BA)2(MA)n−1PbnBr3n+1 (n = 1, 2, 3) (BA = butylammonium, MA = methylammonium) was used as a platform to investigate the response of 2D perovskites to ultraviolet (UV) light. Single crystals were synthesized and nanoflakes were prepared by mechanical exfoliation. In the optical microscope, the phenomenon of photobleaching had been observed, where nanoflakes gradually lost their original color and become transparent in response to UV light illumination. A series of X-ray diffraction and UV-Vis spectroscopy measurement revealed the transition from a crystalline structure to an amorphous structure, accompanied change in optical property of the transparent phase. Fluorescence microscopy was employed to monitor the changes in PL emission. The results clearly demonstrated a blue-to-green redshift in PL emission of the nanoflakes with n > 1, which can be attributed to degradation of the pristine crystals and the formation of MAPbBr3 nanoclusters. Additionally, analysis employing electron microscopes confirmed that (BA)2(MA)n−1PbnBr3n+1 eventually degrade to PbBr2 under illumination. By utilizing atomic force microscope to measure the thickness of the nanoflakes before and after illumination, it was determined that the reduction in thickness could be attributed to the loss of organic layers. Furthermore, Fourier transform infrared spectroscopy provided evidence of the escape of organic molecules induced by illumination, and the BA molecules were more easily escape than MA molecules which can be attributed to their different locations among layers. It was observed that BA molecules exhibited a higher propensity to escape compared to MA molecules, which can be attributed to their distinct locations within the layers. This comprehensive investigation provides valuable insights into the mechanism underlying light-induced changes in 2D perovskites and paves the way for the design of photostable optoelectronic applications based on 2D perovskite materials. |
| Rights: | All rights reserved |
| Access: | open access |
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