Quasi-2D Halide Perovskite Films for High-Performance Photodetectors

Abstract

Organic-inorganic halide perovskites have been proven to be one kind of the most promising optoelectronic materials for photodetectors, light-emitting diodes, solar cells, etc. However, the stability of these charming materials is too poor which is the main barrier of their commercial applications. To solve the stability problem, one kind of quasi-2D perovskites, Ruddlesden-Popper (RP) type halide perovskites, was proposed. Although the RP type halide perovskites can enhance the stability of the perovskites in humid environments, their performance is still far from satisfactory in many other ambient conditions. Accordingly, in this work, we focused on the improvement of the optoelectronic performance and stability of the RP type halide perovskites, and one new kind of quasi-2D perovskites, Dion-Jacobson (DJ) type halide perovskites were also introduced and proved to be a perfect alternative to the RP type.

First, RP type halide perovskite films with iso-butylamine (iBA) spacer cations were fabricated by the spin-coating method. We found the graded phase distribution in this RP type halide perovskite film along the out-of-plane direction. Thanks to this graded phase distribution, one built-in electric potential can form automatically. Utilizing this unique nature of the RP type perovskites, vertical-structure self-powered photodetectors were configured. This kind of photodetector showed expressive responsivity and response speed, which is even better than most reported RP type halide perovskites-based photodetectors powered by external bias voltages. Meanwhile, this vertical-structure photodetector also showed ultra-high mechanical stability. After being bent for thousands of times, its photocurrent still maintained the initial value. These results improved the performance and stability of the RP type halide perovskites-based photodetectors effectively.

To further enhance the optoelectronic properties and stability of the RP type halide perovskites, bication ethylenediammonium (EDA) were also introduced. Because of the short alkyl chain length of EDA, it could not only serve as the normal cations but also the spacer cations of the 2D halide perovskites. When EDA acted as the normal cations, it could make the 2D perovskite films more intact and accordingly the optoelectronic performance was also improved. When EDA acted as the spacer cations, the mechanical stability was enhanced because of its bication nature without weak van der Waals interactions.

Finally, another bication N,N-dimethyl-1,3-propanediamine (DMPDA) were also used as the spacer cation to form the DJ type halide perovskites. The photodetection performance and stability of this DJ type halide perovskites were detailly studied and compared with the conventional RP type halide perovskites. The responsivity of the DJ type perovskite-based photodetector was several times larger than that of the RP type. More importantly, the stability of these halide perovskites was improved significantly. After being stored at a humidity of 68%, illuminated by a high-tensity laser, heated to 100 ºC, radiated by an electron beam, and bent for thousands of times, the DJ type halide perovskite could still maintain its optoelectronic properties, which was much superior to the RP type counterparts.

Date of Award	2 Aug 2023
Original language	English
Awarding Institution	City University of Hong Kong
Supervisor	Johnny Chung Yin HO (Supervisor)